PEER REVIEW HISTORY ARTICLE DETAILS VERSION 1 - REVIEW. Lone Schmidt Department of Public Health University of Copenhagen Denmark 04-Oct-2013

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1 PEER REVIEW HISTORY BMJ Open publishes all reviews undertaken for accepted manuscripts. Reviewers are asked to complete a checklist review form (see an example) and are provided with free text boxes to elaborate on their assessment. These free text comments are reproduced below. Some articles will have been accepted based in part or entirely on reviews undertaken for other BMJ Group journals. These will be reproduced where possible. TITLE (PROVISIONAL) AUTHORS REVIEWER REVIEW RETURNED GENERAL COMMENTS ARTICLE DETAILS Socioeconomic variations in female fertility impairment - a study in a cohort of Portuguese mothers Correia, Sofia; Rodrigues, Teresa; Barros, Henrique VERSION 1 - REVIEW Lone Schmidt Department of Public Health University of Copenhagen Denmark 04-Oct-2013 This is an interesting study from Portugal on fertility and female infertility in a population-based cohort of women having recently delivered a child. The study is thoroughly conducted and detailed data for measuring fertility/infertility has been collected. Results are presented clearly and the discussion is relevant and interesting. Major comments 1. The exclusion of women having a partner diagnosed with male factor infertility I find it questionable whether it is a good idea to exclude the N=105 women having a partner diagnosed with male factor infertility. I assess the reason for this exclusion is to focus the analyses on socio-economic associations with female infertility and unexplained infertility? However, the exclusion of women with male factor infertility does not necessarily exclude men s impact on infertility/fertility. For example high female BMI in this study was significantly associated with time to pregnancy (TTP) > 12 months. A similar previous study among women having achieved pregnancy/childbirth showed a doubled risk of TTP > 12 months among couples where both partners had high BMI (Ramlau-Hansen et al., Human Reproduction, 2007) and women having high BMI is frequently having a partner with high BMI as couples often share life style. Also advanced male age have an impact on infertility and combined advanced age for women and their partner has e.g. showed a 5-6 fold increase in risk of miscarriage (de la Rochebrocard et al., Human Reproduction 2002). This to say, that I

2 will recommend to keep women with male partner infertility in the analyses. Also keeping these women will make the study more comparable with similar studies when comparing for example the infertility prevalence rates and distributions of infertility diagnosis. In case the authors still prefer not to include women with partner s having male factor infertility, I recommend to underline this in the title of the paper, in tables and throughout the text. It is highly important for readers to be aware of this exclusion when comparing results from this study with results based on other similar studies not having excluded participants having male factor infertility. 2. Use of concepts impaired fertility and impaired infertility The infertility/fertility research scientific literature is characterized by using a range of different concepts and with identical concepts defined differently making comparison across studies difficult. This study is based on a population-based cohort of women having given birth recently and I will recommend the use of the concept time to pregnancy (TTP) > 12 months instead of impaired fertility. By using prolonged TTP in this study it is emphasized that the cohort is based on mothers and do not include women having involuntarily never given birth or who had never achieved a pregnancy to 23 weeks gestation. Another suggestion could be to use the concept infertility as it is defined clinically by WHO and ICMART: a disease of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse (Zegers-Hochshild et al., Human Reproduction 2009). If the authors keep the concept impaired fertility I will recommend to state impaired female fertility and not also to use the concept impaired infertility (see e.g. p. 12) and infertility (see e.g. p. 11). 3. Stress and anxiety a clinical diagnosis for problems conceiving? In Table 2 is stated that 38% achieved a clinical diagnosis of stress and anxiety for problems conceiving. I wonder whether I understand this correctly: Has a medical doctor given this as a diagnosis/reason for infertility to the women? Or is this the women s own assessment why they had difficulties in conceiving? A recent meta-analysis among women in ART treatment showed no association between pre-treatment anxiety level and depressive symptom level and probability of pregnancy after one ART-cycle (Boin et al. BMJ, 2011). Please, clarify.

3 I wonder where unexplained infertility is categorized? Also please clarify what use of medication for infertility problems include. Is it hormonal treatment or does it also includes medication to reduce anxiety and stress (as this is mentioned as a clinical diagnosis for problems in conceiving)? 4. Socio-economic differences in infertility/ttp > 12 months Other large, representative population-based (i.e., NOT clinic-based samples) studies have shown no association between socioeconomic position and infertility (e.g. Bhattacharya et al., Human Reproduction, 2009; Schmidt et al., British Journal of Obstetrics and Gynecology, 1995). I recommend the authors in the Discussion Section to include and discuss also studies finding no association between socio-economic position and infertility. Minor comments 1. Abstract Please, clarify whether the results regarding education level and TTP > 12 months were adjusted for age (and other relevant confounders). 1. Key messages - clarifications A. I suggest to explain directly in the text how education is associated with lifetime prolonged time to pregnancy. It is difficult to be sure to understood correctly what negatively associated with indicates without having read the results/abstract. B. important in explaining inequalities in fertility. Isn t it more precise to state inequalities in waiting time to pregnancy > 12 months instead of fertility as the analyses is not focused on live births? 2. Strengths and limitations In bullet 2 I think a last part of the sentence is missing. 3. Introduction infertility seems to have increased in most countries? It is obvious that across a range of countries there has been an increase in numbers of people seeking medically assisted reproduction. However, very few population-based studies have

4 REVIEWER REVIEW RETURNED GENERAL COMMENTS measured infertility prevalences in the same geographical area over a year timespan. Bhattacharya et al. (Human Reproduction, 2009) found no changes in infertility prevalence in Scotland, but Rostad et al. (Acta Obstet Gynecol Scand, E-pub ahead of print) found a significant increase in infertility prevalence. So I have doubts whether it is correct to state that infertility seems to have increased in most countries. 4. Table 1 Please, add Montly income in the column heading. 5. Results p. 10, first paragraph Please, clarify that it is 39% of primigravidae with TTP > 12 months and 35% of multigravidae where concection has taken 3 years or more. Melanie Morris LSHTM UK 18-Oct-2013 Overall This was an interesting study, generally well-written and using appropriate methodology. I feel the message of the paper is somewhat confused as I am not sure there are strong enough findings here to justify the conclusions. There are some substantial areas that need amending, but re-focus on the research question and main variables of interest could result in a clearer paper. General points Negative vs positive association confusion use natural language to describe results i.e. higher education level in primigravidae was associated with less fertility impairment Define primigravidae / mutligravidae carefully including women with previous live births only (parity) or any previous pregnancy (true meaning of gravidity)? Lifetime fertility : in this study, only fertility for this pregnancy measured? Not lifetime fertility? Avoid referring to associations with fertility ; this study looks at fertility impairment Several long complex sentences / paragraphs, often difficult to follow arguments and the story of the research

5 Title - Some English grammar corrections needed somewhat misleading not fertility, rather fertility problems (i.e. not how quickly women fall pregnant by their SES) Abstract specify that the list of characteristics associated with fertility impairment (p.2, line 38-39) is from unadjusted analysis show test for trend p value in results for education level and fertility impairment in primigravid (p.2, line 47) as CIs do overlap these results not shown in main text, only in figure Conclusion overstated, unclear and not directly related to aims: - clearly shows social factors are important (p.2, line 51)? Only education level, and only in primigavidae - Aims are to assess how socioeconomic conditions impact on the prevalence... (p.2 line 10-11): conclusion mentions biological mechanisms? - Unclear what those related to traditional lifestyle means Article Summary p.3 line 16: Lifetime fertility? Or just for this pregnancy? p.3 line 20:...not in women with a previous child =multiparous; multigravid=any previous pregnancy p.3 line21: No evidence for other individual influences being important in explaining social inequalities p.3 line 37: word(s) missing at end of sentence. This also seems to be the only place where this limitation is mentioned. It is an important one to discuss but I couldn t find it in the Discussion Last limitation also not dealt with fully in the body of the text and isn t really of relevance to this study; raises many questions that are not answered later: why/how would policies impact etc? Introduction p.4 line 37: Need to pick apart fertility (ability to conceive, choice taken by couple to try for a baby, choice of couple how many children to have) and fertility impairment i.e. decline in fertility or increase in infertility. Would have liked to see more assessment of the evidence relating to the factors of main interest here: education, income, occupation. Methods Why were only 70% of eligible women invited? Why not all? Why was another group of women interviewed during pregnancy? How might this have impacted the study? - Later it says they were excluded: why mention them at all?

6 Move last part of paragraph on p.6 to start of Results (from The final sample... p. 6 line 19); this will also mean that the variables will have been defined previously making it easier to understand. - add a flow chart to show sample selection Table 1 (move to Results) - It is hard at first glance to understand how the sample has higher income but more blue collar workers than the excluded; it s obviously to do with the relative numbers in each category but it s hard to understand this from the table as there are no numbers included by each column - Add an assessment of the significance of the difference between included / excluded are the %s in highest income/blue collar really different? Results Give more numerical data throughout the text including p values. Clarify sentences - p.4 line 51 Overall. I assume this was 39% of primigravidae with fertility problems had taken three years or more. - p.4 line 56: Seven percent of all women - Would be helpful to include n/n for percentages. I don t think the paragraph starting on p.4 line 55 is relevant to the research question and could be omitted, along with Table 2 Table 3: Infection disease (not good English: Infection would be enough) if the denominator is different put these results in a separate section of the table with their N above them otherwise it is misleading and too easily confused for 1.6% (e.g.) of the total number Some women who say they did not plan this pregnancy also report trying for more than a year to have this baby? In Table 3, 81.4% of women who planned the pregnancy had fertility impairment. Presumably this means that 18.6% of women who didn t plan the pregnancy had fertility impairment i.e. took >1yr to conceive it. A problem with understanding the women had of the question perhaps? Explain in Discussion? Discussion Negatively (p.14 line 55) and positively (p.13 line 28) associated both used to describe the results which is it? Preferably use natural language in the Discussion as mentioned above to avoid this problem. Remove mention of help-seeking Make the relevance of other variables e.g. obesity / smoking / age at first intercourse more obvious. Too much discussion of these and other factors without explaining how they relate to SES (not sure there is much justification for including age at first intercourse as a variable at all or the ethics of asking the question of participants in the first place, given that the

7 Reviewer Name: Lone Schmidt authors say This indicator may not have captured sexually transmitted infections. Was there a priori evidence that it might?) p.16 this paragraph needs to be split up and re-written to help the reader follow the argument here I found it confusing, and difficult to relate to the research question. Relevance of mentioning impact of maternity policies on family planning would this impact the ability to conceive once couples are trying for a baby? Explain, or leave out. Last paragraph is vastly overstated only one association with one aspect of social circumstances was found in one sub-group of women. Not sure where the evidence was presented that this appears to be mediated by biological mechanisms other than those related to traditional lifestyles? Or for the rest of this paragraph VERSION 1 AUTHOR RESPONSE Major comments 1. The exclusion of women having a partner diagnosed with male factor infertility I find it questionable whether it is a good idea to exclude the N=105 women having a partner diagnosed with male factor infertility. I assess the reason for this exclusion is to focus the analyses on socio-economic associations with female infertility and unexplained infertility? However, the exclusion of women with male factor infertility does not necessarily exclude men s impact on infertility/fertility. For example high female BMI in this study was significantly associated with time to pregnancy (TTP) > 12 months. A similar previous study among women having achieved pregnancy/childbirth showed a doubled risk of TTP > 12 months among couples where both partners had high BMI (Ramlau-Hansen et al., Human Reproduction, 2007) and women having high BMI is frequently having a partner with high BMI as couples often share life style. Also advanced male age have an impact on infertility and combined advanced age for women and their partner has e.g. showed a 5-6 fold increase in risk of miscarriage (de la Rochebrocard et al., Human Reproduction 2002). This to say, that I will recommend to keep women with male partner infertility in the analyses. Also keeping these women will make the study more comparable with similar studies when comparing for example the infertility prevalence rates and distributions of infertility diagnosis. In case the authors still prefer not to include women with partner s having male factor infertility, I recommend to underline this in the title of the paper, in tables and throughout the text. It is highly important for readers to be aware of this exclusion when comparing results from this study with results based on other similar studies not having excluded participants having male factor infertility. Answer: Thank you for this helpful comment. We are aware of the difficulty to disentangle women s infertility from the males causes along with the effects of shared adverse exposures. The revised manuscript includes a discussion of this aspect in more detail. This study was designed towards women s socioeconomic characteristics and their impaired fertility. Male recognised causes for infertility were excluded, since these causes are less likely to be associated, at least directly, with women s social conditions. As suggested, we underlined this in the title and throughout the manuscript. Even so, for a subgroup of primigravidae for whom we have data for the fathers BMI (n=813) we estimated the association between women s social conditions and infertility adjusted for the shared BMI (couple under/normal weight; women overweight/obese and male under/normal weight; women

8 under/normal weight and male overweight/obese; couple overweight/obese) and the results were similar. The same was conducted regarding couples age. We did not find differences in the relation between maternal sociodemographics and impaired fertility. Despite not showing these results we explained in dept detail in the discussion (page 18-19): We acknowledge that we might not have totally dissociated the women causes from male or even the couples causes along with the effects of shared risk factors. Studies show that the risk of infertility is higher if both partners present obesity 35 as when both are older 36. For a subgroup of primigravidae (n=813) for whom we have data from the father at the moment of birth (self-administered questionnaires) we conducted the same analysis adjusting for the shared overweight/obesity and age over 35 years and the relation between education and infertility did not significantly changed (data not show). 2. Use of concepts impaired fertility and impaired infertility The infertility/fertility research scientific literature is characterized by using a range of different concepts and with identical concepts defined differently making comparison across studies difficult. This study is based on a population-based cohort of women having given birth recently and I will recommend the use of the concept time to pregnancy (TTP) > 12 months instead of impaired fertility. By using prolonged TTP in this study it is emphasized that the cohort is based on mothers and do not include women having involuntarily never given birth or who had never achieved a pregnancy to 23 weeks gestation. Another suggestion could be to use the concept infertility as it is defined clinically by WHO and ICMART: a disease of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse (Zegers- Hochshild et al., Human Reproduction 2009). If the authors keep the concept impaired fertility I will recommend to state impaired female fertility and not also to use the concept impaired infertility (see e.g. p. 12) and infertility (see e.g. p. 11). Answer: We appreciate this helpful comment. We had opted the term impaired fertility because our sample represents truly fertile women and the term infertility could confuse the manuscript. We think that prolonged time-to-pregnancy may not be the best definition because, although this sample represents women that had a successful pregnancy, the definition of fertility impairment does not necessarily refer to the current pregnancy and/or the moment previous to conception. Women with impaired fertility were those who said they had ever tried to conceive for more than a year without success. Among impaired multigravidae, 39% achieved the current pregnancy in less than one year. For these women presenting ever in life prolonged time-to-pregnancy we do not know what was the previous reproductive outcome. Based on this, we agree in the use of the concept impaired female fertility and changes are tracked in the revised manuscript. 3. Stress and anxiety a clinical diagnosis for problems conceiving? In Table 2 is stated that 38% achieved a clinical diagnosis of stress and anxiety for problems conceiving. I wonder whether I understand this correctly: Has a medical doctor given this as a diagnosis/reason for infertility to the women? Or is this the women s own assessment why they had difficulties in conceiving? A recent meta-analysis among women in ART treatment showed no association between pretreatment anxiety level and depressive symptom level and probability of pregnancy after one ARTcycle (Boin et al. BMJ, 2011). Please, clarify. I wonder where unexplained infertility is categorized? Also please clarify what use of medication for infertility problems include. Is it hormonal treatment or does it also includes medication to reduce anxiety and stress (as this is mentioned as a clinical diagnosis for problems in conceiving)?

9 Answer: Women were asked if a doctor made diagnosis was provided. The questionnaire on clinical diagnosis included closed questions (yes or no) for hormonal disturbances, polycystic ovary syndrome, tubal obstruction and endometriosis. Stress and anxiety resulted from other causes reported by women. Misconceptions about the diagnosis are possible and unexplained infertility may have been interpreted by women as stress and anxiety. The drugs used by women declaring medication for infertility were predominantly hormonal treatments or ovulation stimulants and did not include treatment for stress and anxiety. Twenty-five percent of women referring stress and anxiety were under infertility medication regimens while the proportion was 75% among those with other clinical diagnosis. Also, only 14 (3%) women that reported the diagnosis of stress and anxiety were using psycholeptics or antidepressants (vs. 14(6%) of women with other diagnosis, p=0.149). According to what was suggested by the other reviewer, considering that data on the help-seeking behavior and the related diagnosis could not be the most important to the main objective of this manuscript we have opted to remove the table 2 and provide a summarized description of this, focusing on the aspects that might be relevant to understanding the main results. However, the table remains as a supplementary file. 4. Socio-economic differences in infertility/ttp > 12 months Other large, representative population-based (i.e., NOT clinic-based samples) studies have shown no association between socio-economic position and infertility (e.g. Bhattacharya et al., Human Reproduction, 2009; Schmidt et al., British Journal of Obstetrics and Gynecology, 1995). I recommend the authors in the Discussion Section to include and discuss also studies finding no association between socio-economic position and infertility. Answer: Thank you for pointing this out. We included these aspects in the discussion (2nd paragraph of discussion, page 16). The association between education and fertility impairment was previously described in other large population-based European studies among primiparous women 11, 17, and was explained by the effect of education on decreasing the exposure to adverse lifestyles, risky sexual behaviour and body weight. Contrarily, an increase of infertility with increasing education was also found in other study in the United Kingdom although the authors argue that reflects the increasing recognition of the fertility problem among this group of women and does not result from a biological reduction in the ability to conceive 24. Other studies in Denmark 25 and Scotland 26 found no relation between social class / education and infertility. These different results may reflect the huge geographical variations of socio inequalities in health 27 besides differences in the definitions and in the socioeconomic indicators used. Minor comments Abstract Please, clarify whether the results regarding education level and TTP > 12 months were adjusted for age (and other relevant confounders). Answer: The sentence was re-written appropriately: In crude analysis we found women with infertility to be ( ). In multivariate models there was a significant independent association between ( ) 1. Key messages - clarifications A. I suggest to explain directly in the text how education is associated with lifetime prolonged time to pregnancy. It is difficult to be sure to understood correctly what negatively associated with indicates without having read the results/abstract. Answer: We appreciate the comment and the sentence was properly changed for: In primigravidae, but not in women with a previous pregnancy, increasing education was associated with a decrease in female fertility impairment, independently of age and other behavioural factors. B. important in explaining inequalities in fertility. Isn t it more precise to state inequalities in waiting time to pregnancy > 12 months instead of fertility as the analyses is not focused on live

10 births? Answer: We have tried to clarify the message and the sentence was re-written as: This study shows that the association between education and fertility impairment was not totally justified by lifestyles generally used to explain social inequalities in infertility. 2. Strengths and limitations In bullet 2 I think a last part of the sentence is missing. Answer: We are sorry for this error, the sentence was appropriately changed. Data about infertility was retrospectively collected after birth and misclassification may have occurred. 3. Introduction infertility seems to have increased in most countries? It is obvious that across a range of countries there has been an increase in numbers of people seeking medically assisted reproduction. However, very few population-based studies have measured infertility prevalences in the same geographical area over a year timespan. Bhattacharya et al. (Human Reproduction, 2009) found no changes in infertility prevalence in Scotland, but Rostad et al. (Acta Obstet Gynecol Scand, E-pub ahead of print) found a significant increase in infertility prevalence. So I have doubts whether it is correct to state that infertility seems to have increased in most countries. Answer: Thank you for this comment. We apologize for not be clear in the text. When stating that infertility seem to have increased in most countries we were expressing the trends in the fertility rates in a demographic perspective. We have changed the text and referenced the recent published paper along with the one from Bhattacharya et al.: (Page 5, paragraph 2) Over the recent decades, several countries showed a decrease in their total fertility rates (in a demographic perspective as the total number of children per woman) 9 but it is not consensual a decline in biological fertility capacity. Some authors report an increase of the ability to conceive explained by better social conditions and less sexually transmitted infections 10-11, others a fertility decrease related with women s postponement of childbearing age and adverse lifestyles while others found no differences in trends. 4. Table 1Please, add Montly income in the column heading. Answer: The table was changed. 5. Results p. 10, first paragraph Please, clarify that it is 39% of primigravidae with TTP > 12 months and 35% of multigravidae where conception has taken 3 years or more. Answer: The paragraph was appropriately re-written: Within fertility impaired women, 39% (86/219) of primigravidae and 35% (123/348) of multigravidae had taken three years or more to get pregnant. Reviewer Name: Melanie Morris General points Negative vs positive association confusion use natural language to describe results i.e. higher education level in primigravidae was associated with less fertility impairment Answer: We appreciate the comment and the sentence was properly changed for: In primigravidae, but not in women with a previous pregnancy, increasing education was associated with a decrease in fertility impairment (key message, page 4) Define primigravidae / mutligravidae carefully including women with previous live births only (parity) or any previous pregnancy (true meaning of gravidity)?

11 Answer: Previous child was substituted by previous pregnancy Lifetime fertility : in this study, only fertility for this pregnancy measured? Not lifetime fertility? Answer: Women with impaired fertility were those who had tried to conceive for more than a year without success, ever in their reproductive life up to the current pregnancy. In this sense we believe that can be defined as lifetime infertility. However, we agree that not sampling postmenopausal women, lifetime infertility may be misunderstood. Because of that we removed the term lifetime in the manuscript. Avoid referring to associations with fertility ; this study looks at fertility impairment Answer: The appropriate changes were conducted. As suggested by the other reviewer we have emphasized female fertility impairment. Several long complex sentences / paragraphs, often difficult to follow arguments and the story of the research - Some English grammar corrections needed Answer: Thank you for this comment. We rewrote the manuscript and we hope it is now clearer. Title somewhat misleading not fertility, rather fertility problems (i.e. not how quickly women fall pregnant by their SES) Answer: The tile was changed to: Socioeconomic variations in female fertility impairment - a study in a cohort of Portuguese mothers. Abstract specify that the list of characteristics associated with fertility impairment (p.2, line 38-39) is from unadjusted analysis Answer: The sentence was re-written appropriately: In crude analysis we found women with impaired fertility to be older, less educated, more likely to have planned the current pregnancy and to be overweight/obese; but they had similar levels of income or occupation. show test for trend p value in results for education level and fertility impairment in primigravid (p.2, line 47) as CIs do overlap these results not shown in main text, only in figure Answer: We have included p for trend in the abstract and the odds ratio estimates were added to the main the text (page 14) Compared to those with 6 or less years of education, having 7 to 9, and more than 12 years of formal education was associated with lower odds of having infertility [OR (95% CI) vs. 6y: 7-9y: 0.85 ( ); 10-12y: 0.34 ( ); >12y: 0.24 ( ), ptrend<0.001]. Conclusion overstated, unclear and not directly related to aims: - clearly shows social factors are important (p.2, line 51)? Only education level, and only in primigravidae - Aims are to assess how socioeconomic conditions impact on the prevalence... (p.2 line 10-11): conclusion mentions biological mechanisms? - Unclear what those related to traditional lifestyle means Answer: Thank you for these comments. We recognize that the aims of the manuscript as written could be misleading. This study aimed to assess the association of socioeconomic conditions and female impaired fertility. In primigravidae, we found a clear dose-response association with education. We have adjusted for behavioural characteristics that are traditionally described to be the ones that explain the relation of social circumstances with infertility (besides maternal age and pregnancy planning, overweight and age at first intercourse were the variables that remained important in the models). For those, the biological effect is acknowledged. Since the association between education

12 and fertility impairment remained statistically significant after adjustment we assume that other socially-related characteristics may be involved besides the ones described. We agree in changing the abstract conclusion for: This study shows that education might be important in the understanding of female fertility impairment, particularly among first time pregnant women. It also points out that the association is not totally explained by lifestyles generally used to disclose this relation. Article Summary p.3 line 16: Lifetime fertility? Or just for this pregnancy? Answer: As written in the third comment. Women with impaired fertility were those who had tried to conceive for more than a year without success, ever in their reproductive life up to the current pregnancy. In this sense we believe that can be defined as lifetime infertility. However, we agree that not sampling postmenopausal women, lifetime infertility may be misunderstood. Because of that we removed the term lifetime in the manuscript. p.3 line 20:...not in women with a previous child =multiparous; multigravid=any previous pregnancy Answer: The sentence was re-written as: in primigravidae but not in women with a previous pregnancy. p.3 line21: No evidence for other individual influences being important in explaining social inequalities Answer: This sentence was re-written as: This study shows that the association between education and fertility impairment was not totally justified by lifestyles generally used to explain social inequalities in infertility. p.3 line 37: word(s) missing at end of sentence. This also seems to be the only place where this limitation is mentioned. It is an important one to discuss but I couldn t find it in the Discussion Answer: We are sorry for this error, the sentence was appropriately changed. Data about female fertility impairment was retrospectively collected after birth and misclassification may have occurred. The discussion of this limitation was considered in the discussion now: Female fertility impairment was retrospectively collected after birth and misclassification may have occurred. However, if misclassification was differential we expect to less educated women to underreport their status. If so, even greater socioeconomic gaps would be observed. Last limitation also not dealt with fully in the body of the text and isn t really of relevance to this study; raises many questions that are not answered later: why/how would policies impact etc? Answer: This sentence was removed. Introduction p.4 line 37: Need to pick apart fertility (ability to conceive, choice taken by couple to try for a baby, choice of couple how many children to have) and fertility impairment i.e. decline in fertility or increase in infertility. Answer: Thank you for this comment. We have opted to use the term female fertility impairment in the manuscript. Would have liked to see more assessment of the evidence relating to the factors of main interest here: education, income, occupation. Answer: We have changed the introduction and included a more detailed description of these aspects. More highly educated women are more likely to postpone childbearing to an age when the probability of conception decreases and the probability of early pregnancy loss increases They are also

13 more likely to plan pregnancy and to be aware of fertility problems, promoting the decision to seek for help 16. However, less educated women are more likely to be overweight, to smoke and to have more risky sexual behaviour which may negatively impact female fertility Despite the correlation between different dimensions of socioeconomic circumstances, their components may impact fertility by different mechanisms. Income allows easier or faster access to health services, namely those with fertility advice, as to material resources as better food or services promoters of better health 20. Occupation may also relates infertility via labour pressure and working schedules or by environmental exposures as solvents or other pollutants 18. Methods Why were only 70% of eligible women invited? Why not all? Answer: The detailed description is now included in the main text. In all, 70% of the eligible mothers were invited (not all eligible mothers were invited due to logistic constraints, namely availability of human resources; in these circumstances, women were invited in a basis of first come, first served) and (...) Why was another group of women interviewed during pregnancy? How might this have impacted the study? - Later it says they were excluded: why mention them at all? Answer: This study was conducted within a population-based cohort study. The target population for recruitment included all women delivering in public hospitals from the Metropolitan Region of Porto. Because of specific research questions, namely on fetal growth, a subgroup of women was invited to participate at the first trimester of pregnancy. All these women had hospital-based prenatal care (further were excluded those that did not deliver in the referred maternity units). They were excluded from the current analysis because data was collected at different moments during pregnancy (first, second and third trimesters) which may affect the report of some of the included variables, namely regarding fertility impairment, pregnancy planning or pre-pregnancy weight. Despite this, they were part of the sampling frame and so we mention them in the methods. They were less educated than the included participants. Assuming that we have correctly estimated the association between education and fertility impairment, the exclusion of this group decreased the power of the current study to detect real differences, not biasing the results. Move last part of paragraph on p.6 to start of Results (from The final sample... p. 6 line 19); this will also mean that the variables will have been defined previously making it easier to understand. - add a flow chart to show sample selection Table 1 (move to Results) - It is hard at first glance to understand how the sample has higher income but more blue collar workers than the excluded; it s obviously to do with the relative numbers in each category but it s hard to understand this from the table as there are no numbers included by each column - Add an assessment of the significance of the difference between included / excluded are the %s in highest income/blue collar really different? Answer: Thank you for this suggestion. We have included a flow chart and moved the last part of the paragraph and the table 1 to the results. In the table we added the crude numbers and the statistical significance between included and excluded. About these differences we are very sorry for the wrong description of the results in the first version of the manuscript. As seen in the table, the only differences found between included and excluded participants were for smoking habits (more frequent among included women: 26% vs. 20%) and in age (29 vs. 30 years). Although the included participants show high income and high proportion of blue-collar workers, these differences were not statistically significant. Results Give more numerical data throughout the text including p values.

14 Answer: We have changed the manuscript according this suggestion. Clarify sentences -p.4 line 51 Overall. I assume this was 39% of primigravidae with fertility problems had taken three years or more. Answer: This was changed accordingly: Within fertility impaired women, 39% (86/219) of primigravidae and 35% (123/348) of multigravidae had taken three years or more to get pregnant. - p.4 line 56: Seven percent of all women Answer: Changed in the revised manuscript: Seven percent of women (517/7402) had sought medical help because they could not get pregnant and 71% reported a clinical diagnosis. - Would be helpful to include n/n for percentages. Answer: Changed in the manuscript when no numbers are provided in the tables. I don t think the paragraph starting on p.4 line 55 is relevant to the research question and could be omitted, along with Table 2 Answer: We agree that the detailed description of the help-seeking behaviour and consequent diagnosis may not be of major importance to the research question. However we think this description is useful to understand what women with fertility impairment this sample represents and what was the relation between education and seeking behaviour. Based on this we opted to include the table as a supplementary file and provide a summarized description of this topic, focusing on the aspects that might be relevant to understanding the main results. Table 3: Infection disease (not good English: Infection would be enough) if the denominator is different put these results in a separate section of the table with their N above them otherwise it is misleading and too easily confused for 1.6% (e.g.) of the total number Answer: The table was changed according the suggestions. Some women who say they did not plan this pregnancy also report trying for more than a year to have this baby? In Table 3, 81.4% of women who planned the pregnancy had fertility impairment. Presumably this means that 18.6% of women who didn t plan the pregnancy had fertility impairment i.e. took >1yr to conceive it. A problem with understanding the women had of the question perhaps? Explain in Discussion? Answer: This aspect reflects the outcome definition that was used we did not considered time-topregnancy for the index pregnancy. As referred above, while in primigravidae fertility impairment was related to the current pregnancy, the same was not necessarily true for multigravidae. The proportion referred above describes a group of women for whom we can be sure that impairment occurred in the previous pregnancy. We hope to have made that clearer in the revised manuscript. Discussion Negatively (p.14 line 55) and positively (p.13 line 28) associated both used to describe the results which is it? Preferably use natural language in the Discussion as mentioned above to avoid this problem. Answer: The paragraphs were changed accordingly and we hope it is clearer now. Results, page 14: a significant positive association was observed between educational level and fertility higher education level was associated with a decrease in female fertility impairment ( ) Discussion, page 16, first paragraph: Among primigravidae who had recently delivered a live birth we found that higher education was associated with a decrease in female fertility impairment independently of age and other behavioural factors, but no other socioeconomic indicator was related. Remove mention of help-seeking

15 Answer: As answered in the previous comment, we kept a briefly description on the results section. We think it is useful to refer the low prevalence of help-seeking once we are discussing a possible modification of the health behaviours based on clinical advice. Make the relevance of other variables e.g. obesity / smoking / age at first intercourse more obvious. Too much discussion of these and other factors without explaining how they relate to SES (not sure there is much justification for including age at first intercourse as a variable at all or the ethics of asking the question of participants in the first place, given that the authors say This indicator may not have captured sexually transmitted infections. Was there a priori evidence that it might?) Answer: As it is referred in the literature, we found these adverse behavioural characteristics to be more frequent among less educated women. This pattern was already described for this cohort. In the results, for the variables that remained in the model, we reinforced the differences. Page 12, final paragraph: Low educated women (<6 years) were more likely than more educated (>12 years) to be overweight or obese (45% vs. 20%) and to report early age at sexual initiation (<16 years: 12% vs. 2%). We also included this in the discussion. Page 16, 2nd paragraph: Our results were only partly explained by variations in women s behaviours. It is known, and was also previously found for this cohort, that smoking and obesity are more frequent in socially deprived women 21. We agree that age at the first sexual intercourse may be a sensitive question. However, data collection was conducted with professional and trained interviewers assuring privacy and the proportion of women not answering this question was low. Also, in the gynaecological and obstetric visits this topic is frequently assessed. It is known that age at the first sexual intercourse is related with social conditions, being more frequent among less affluent groups (Vesely SK J Adolesc Health. 2004). It is also known that increases probability of sexually transmitted infections, by increasing the number of sexual partners (Andersson-Ellström A, Acta Obstet Gynecol Scand, 1996). In this framework, we believe that this variable should be considered. However, as a proxy indicator, has its limitations and may have not exactly measured sexually transmitted infections and so, the association between education and infertility remained statistically significant. We hope is clearer now in the manuscript. Page 17, 2nd paragraph: It is known that early age at the first sexual intercourse may be associated with a higher risk of infertility because of the higher probability of sexually transmitted diseases 30. It is also more frequent among least affluent women. In our study it did not entirely explain the association between education and fertility impairment, probably because this indicator may have not fully captured sexually transmitted infections. p.16 this paragraph needs to be split up and re-written to help the reader follow the argument here I found it confusing, and difficult to relate to the research question. Answer: The paragraph was re-written and we hope that is clearer now. Relevance of mentioning impact of maternity policies on family planning would this impact the ability to conceive once couples are trying for a baby? Explain, or leave out. Answer: Thank you for the suggestion. We agree that is clearer to leave out. Last paragraph is vastly overstated only one association with one aspect of social circumstances was found in one sub-group of women. Not sure where the evidence was presented that this appears to be mediated by biological mechanisms other than those related to traditional lifestyles? Or for the rest of this paragraph Answer: According to this comment and the previous one about the abstract conclusion we have changed the manuscript conclusion: This study shows that social circumstances, particularly education, might be important in

16 understanding patterns of fertility impairment. Their impact seems to depend on previous reproductive experience. Among first time pregnant women, infertility decreased with increasing education. This relation was not totally explained by lifestyles generally used to disclose this relation. Please see the answer to the comment about the abstract conclusion with the explanation about the mechanisms involved. REVIEWER REVIEW RETURNED GENERAL COMMENTS REVIEWER REVIEW RETURNED GENERAL COMMENTS VERSION 2 REVIEW Lone Schmidt Department of Public Health University of Copenhagen Denmark 17-Nov-2013 This manuscript has been revised sufficiently according to previous comments. As a consequence of the study objective the authors have made their best to exclude male factor infertility from the sample. However, when not all respondents having had impaired fertility were medically diagnosed it is not possible to a 100% to exclude male factor infertility. In the sample 62.5% had sought medical help of those reporting imparied fertility; and 71% of these reported a diagnosis. I would prefer the authors to make a short comment on this in the Discussion section - that not all male factor infertility has been possible to exclude. Please, explain in full length (not abbreviations only) positive test results for infection (Table 2, foot note). Melanie Morris LSHTM, UK 18-Nov-2013 Overall This paper is much improved and follows a clearer argument which is now not overstated. The writing still needs to be edited carefully for some remaining idiomatic / grammatical errors. Article Summary p.3 line 28: lifestyles generally used to explain what are these lifestyles? (see below in Discussion) Introduction p.5 line 28: Paragraph starting here is a good addition, but needs some rewording of the English to make sense fully: but it is not consensual a decline in biological fertility capacity. p.5 line 37: refs needed

17 p.6 line 8: the end of another useful paragraph just needing some editing for comprehensibility. Methods Results Not sure why this point wasn t answered? Happy to leave it if other reviewers are happy with it but would be useful to have some discussion of it in the paper. - Why was another group of women interviewed during pregnancy? How might this have impacted the study? Later it says they were excluded (p.7 line 23: Because of the different timing (?) of data collection ): why mention them at all? p.10 line 16: this paragraph works much better here (and the table is clearer), but why not add the p values that are shown in the table? Discussion A much better, fuller discussion section. p.20 line 3: not sure about the unsupported statement that less educated women would be less likely to report having tried for over a year to get pregnant. Is there evidence for this from other studies? If not, it might be more cautious to say that there is no reason to believe that the misclassification would be differential between the education groups. So, if there is only non-differential misclassification, the results could be slightly diluted, so the true results might be more extreme. Concluding paragraph clearer - I still have trouble with this general term lifestyles when I look back at the use of the word through the paper it is hard to pin down what you mean by it. Do you mean smoking, unhealthy eating, obesity? Or occupation, income, age? - Might be clearer to say something like This relationship was not totally explained by other socio-demographic characteristics or lifestyle factors that have previously been found to be important. VERSION 2 AUTHOR RESPONSE Reviewer Name: Lone Schmidt - As a consequence of the study objective the authors have made their best to exclude male factor infertility from the sample. However, when not all respondents having had impaired fertility were medically diagnosed it is not possible to a 100% to exclude male factor infertility. In the sample 62.5% had sought medical help of those reporting imparied fertility; and 71% of these reported a diagnosis. I

18 would prefer the authors to make a short comment on this in the Discussion section -that not all male factor infertility has been possible to exclude. Answer: We have changed this paragraph in the discussion and we hope is clear. Discussion, pages 18-19: It should be born in mind that male reproductive impairments are among the possible causes of the current trends in fertility.34 We have excluded participants whose partners had a clinically recognised male cause of infertility but we cannot completely rule out male factors for infertility. Only 63% of women with impaired fertility sought for medical help and among these, a clinical diagnosis for infertility was provided for 71% of women. So, we acknowledge that we might not have totally dissociated the women causes from male or even the couples causes along with the effects of shared risk factors. - Please, explain in full length (not abbreviations only) positive test results for infection (Table 2, foot note). Answer: We have changed the footnote accordingly. Reviewer Name: Melanie Morris Article Summary - p.3 line 28: lifestyles generally used to explain what are these lifestyles? (see below in Discussion) Answer: As suggested below, the sentence was changed to: This study shows that the association between education and fertility impairment was not totally justified by other socio-demographic and lifestyle characteristics that have been previously reported to explain social inequalities in infertility. Introduction - p.5 line 28: Paragraph starting here is a good addition, but needs some rewording of the English to make sense fully: but it is not consensual a decline in biological fertility capacity. Answer: We hope is clearer in the revised manuscript. The sentence was changed to: Over the recent decades, several countries showed a decrease in their total fertility rates (in a demographic perspective considering the total number of children per woman). However, it is there is no consensus whether it may result from a decline in biological fertility capacity. - p.5 line 37: refs needed Answer: Reference was added. - p.6 line 8: the end of another useful paragraph just needing some editing for comprehensibility. Answer: We hope is clearer now. The sentence was changed to: Occupation may also be related with infertility because of labour pressure, working schedules and psychosocial stress or because of the exposure to environmental pollutants known to decrease implantation rates and increase spontaneous abortion Methods - Not sure why this point wasn t answered? Happy to leave it if other reviewers are happy with it but would be useful to have some discussion of it in the paper. Why was another group of women interviewed during pregnancy? How might this have impacted the study? Later it says they were excluded (p.7 line 23: Because of the different timing (?) of data collection ): why mention them at all?