Estimation of the prevalence and incidence of infertility in a population: a pilot study

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1 FERTILITY AND STERILITY Copyright~ Vol. 5, No.4, April989 Printed in U.S.A. 989 The American Fertility Society Estimation of the prevalence and incidence of infertility in a population: a pilot study Hilary Page, M.F.C.M.* Department of Community Medicine, University of Sheffield Medical School, Sheffield, United Kingdom A pilot study was undertaken to investigate the use of a mailed questionnaire to estimate the prevalence and incidence of infertility in a population, and the demand for medical advice about infertility. The objectives were to investigate the response rate, the acceptability and comprehensibility of the questionnaire, and to provide initial results. After elimination of undelivered questionnaires, a response rate of 82 was obtained. One question was found to be misleading in its wording: this question can be clarified before the questionnaire is used more widely. The results from analysis of the pilot study indicate that 20 to 35 of couples take more than year to conceive, at some stage in their reproductive history. A much larger study, with a sample of approximately 3,500, is required to provide more accurate information. Fertil Steril5:57, 989 A recent survey carried out on behalf of the Family Planning Association showed that 05 (out of 45 responding) Health Districts had no designated services for infertile couples seeking medical help. In order to provide a basis for planning such services, information is required about the incidence, prevalence, and duration of infertility in the population, and the likelihood that infertile couples would wish to seek medical advice. Infertility is defined as the failure to conceive while in a stable relationship and engaging in sexual intercourse without the use of contraception for a period of year or longer. There is no population-based survey of the prevalence or incidence of infertility in the United Kingdom. Estimates of the risk of infertility in women of different age groups can be made from a longitudinal study of women stopping contraception in order to conceive. 2 3 The results indicate that approximately 20 of couples experience primary infertility, and 0 experience secondary inreceived March 2, 988; revised and accepted December 5, 988. * Reprint requests: Hilary Page, M.F.C.M., Lecturer in Epidemiology, Department of Community Medicine, University of Sheffield Medical School, Beech Hill Road, Sheffield SlO 2RX, United Kingdom. Vol. 5, No.4, April989 fertility. However, the women in this study were all aged 25 or over: as approximately half of all first births are to women aged less than 25, it is clear that the women studied were not representative of the child-bearing population as a whole. A Danish survey4 of 935 women aged 25 to 45 showed that 5 had at some time experienced subfecundity, defined as failure to achieve a first pregnancy after engaging in sexual activity without contraception for a period of year or longer. Thirteen percent had experienced secondary subfecundity defined as failure to conceive a second or subsequent pregnancy within a -year period of cohabitation without the use of contraception. A survey in the United States5 showed that 8.5 of all couples in which the woman was aged 5 to 44 did not conceive during a year or more during which they used no contraception. The Aim of the Pilot Study The need for services for infertile couples is influenced not only by the likelihood of a couple experiencing infertility, but also by the duration of infertility and the extent to which a couple desire a child. The incidence of new cases of infertility among the population will increase if the age structure of the population changes to include a higher Page Prevalence and incidence of infertility 57

2 proportion of women around the age of maximum fertility. This is likely to happen as the large birth cohorts of the 960s in the United Kingdom reach young adulthood. A questionnaire* was devised in order to estimate the proportion of married or cohabiting women of childbearing age who have experienced infertility at any time, the prevalence, incidence, and duration of infertility, and the frequency with which medical help was sought for difficulty in becoming pregnant. The aims of the pilot study described here were to estimate the response rate likely to be obtained, and to test the acceptability and comprehensibility of the questionnaire. The range of answers obtained in the pilot study would indicate useful changes to the questionnaire and enable a decision to be reached on sample size and any stratification necessary in a larger survey. The interim results on the prevalence and incidence of infertility might be useful to health care planners who wish to plan on an epidemiologic basis. Patients MATERIALS AND METHODS Six doctors in one group practice used the practice age/sex register to list all women aged 20 to 44. The general practitioners removed from this list any women (2 out of 2,500) whom it was thought were unsuitable to receive the questionnaire. Women who were known to have moved away from the area also were taken off the list. The remaining list of women aged 20 to 44 formed the sampling frame, from which a random sample of 250 women was drawn. A questionnaire and covering letter were mailed to each woman in the sample. A reply paid envelope was supplied. Women were not asked to identify themselves. A survey number was shown on each questionnaire so that survey numbers of respondents could be noted; thus, nonrespondents were identified by survey numbers. The general practitioners were able to link the survey numbers to practice numbers, and to send nonresponders a reminder letter and copy of the questionnaire, 3 weeks later. In the same way, a second reminder was sent after another 3 weeks. A coding system was developed for systematic analysis of the data, by computer. * A copy of the questionnaire is available from the author on request. Ninety-five percent confidence intervals were calculated for the results obtained. For proportions greater than 0., when N was greater than 00, these confidence intervals were calculated using the approximation 95 confidence interval = ±2 X standard error where. ' /P<=P) standard error of a proporton = V ~ Where proportions were smaller than 0., the frequency of the event was treated as if in a Poisson distribution, and 95 confidence intervals were read from standard statistical tables. 6 Calculation of Confidence Intervals for Very Small Proportions The differences between the actual number of events and the upper and lower numerical limits were expressed as a percentage of the total possible number of events, i.e., the total "at risk" of becoming infertile, to give the upper and lower limits of confidence at the 95 level, for the percentag~ infertile. For very small percentages, close to zero, these intervals are of course asymmetrical. Example: Number of prevalent cases of primary infertility, i.e., number of events = 9. Total number of replies with adequate information, i.e., total possible number of events = confidence limits read from statistical tables= 4. to = /53 = = /53 = 5.3. Thus, the prevalence of primary infertility is 9/53 = 5.9, and the 95 confidence interval +5.3 or Response Rate RESULTS The response rates are tabulated in Table. Table Response Rates at Each Mailing Response rate as Nonvalid percent of No. mailings valid Mailing mailed "gone away" mailings Cumulative response rate as percent of total valid mailings Page Prevalence and incidence of infertility Fertility and Sterility

3 Acceptability The high response rate (albeit after two reminders) indicated that the questionnaire was acceptable to the women who received it. One woman telephoned the researcher to say she did not wish to take part in the survey. Four women commented that the survey could not possibly apply to them, as they had completed their families many previously. Comprehensibility Eleven questionnaires were incompletely filled in. One was answered flippantly, the woman stating that it took her "5 minutes" to become pregnant. Answers to one of the questions revealed a misunderstanding that can be avoided by rewording the question. Women were asked whether they "regularly used birth control", and if not, to indicate their feelings about becoming pregnant, by ticking one of three statements: () I wish to become pregnant; (2) I do not mind if I become pregnant; and (3) I would prefer not to become pregnant but am prepared to take the risk, or by giving another reason. Some women indicated that they did not use birth control but gave as the reason for this that they or their husband had been sterilized. These women clearly did not view sterilization as "birth control." The question therefore must be rephrased in order to avoid this misunderstanding. For the analysis of the pilot study, these women were coded as users of birth control. The Prevalence of Infertility The prevalence of infertility is defined here as the number of women aged 20 to 44 who have been engaged in sexual intercourse without conception for more than year, divided by the number of married or cohabiting women aged 20 to 44, in the population. Of the 20 women who replied to the questionnaire, 65 (83) were either married or cohabiting. These formed the population "at risk" of infertility. However, only 53 women gave full information about present or previous duration of non-use of birth control, or had always used birth control. One woman who was a non-user of birth control stated that she and her husband "are not sexually inclined." Twenty other women had been non-users of birth control for more than year. If it is assumed that these women engaged in sexual inter- Vol. 5, No.4, Apri989 course, the prevalence of infertility may be estimated as 20 of 53 (3.0) (confidence interval ± 5.4) of married or cohabiting women. Tables 2 and 3 indicate the levels of primary and secondary infertility, the feelings of infertile women regarding pregnancy, the mean duration of infertility in each group, and the proportion who had sought medical help. It can be seen that the prevalence of primary infertility is 9 of 53 (5.9) (95 confidence interval+ 5.4 or -3.2) and for secondary infertility of 53 (7.2) (95 confidence interval+ 7.8 or -4.8). The Incidence of Infertility The incidence of infertility is defined here as the number of women aged 20 to 44 each year who reach the point at which they have been trying for 2 months unsuccessfully to conceive, divided by the number of married or cohabiting women aged 20 to 44. The incidence of infertility can be calculated using the number of couples who have been trying to conceive for between 2 and 24 months. There were two such women, one with primary, the other with secondary, infertility. Thus, the annual incidence of new cases of infertility among this population of married or cohabiting couples can be estimated to be 2:53 =.3 (95 confidence limits or -.). Experience of Infertility In addition to the 20 women infertile at the time of filling in the questionnaire, there were many who had experienced infertility in the past but had subsequently become pregnant. Among those 34 who had a previous pregnancy, 20 provided information about how long it took to conceive. Ninetythree (78) conceived within year, a further 3, bringing the total to 06 (88.8) within the following year, and a further seven, bringing the total to 3 (94.6) within 3, while the remaining seven took longer than 3 to conceive. Thus, 27 (22) of those who eventually conceived had experienced infertility. The total who ever experienced infertility was therefore 27 who had experienced infertility in the past but had subsequently conceived, plus 9 experiencing primary infertility, and 7 women experiencing secondary infertility at the time of filling out the questionnaire. Thus, a total of 43, out of 53 who gave information, had experienced infertility at some time= 28 (confidence limits± 7.2). Page Prevalence and incidence of infertility 573

4 Table 2 Prevalence of Primary Infertility, Feelings About Pregnancy, Duration oflnfertility and Whether Medical Help Was Sought, and Mean Age at Starting to Try to Conceive Among Women Who Had Not Been Pregnant Before Feelings about onset pregnancy No. of women Mean age of Mean duration No. who sought women at starting of infertility medical help to try to conceive Wish to become pregnant 4 Do not mind if I become pregnant 3 Would prefer not to become pregnant Other reasons 2 Total Range,.4-6 Range, Range,5-6 Range, Range,5-0 Range, Range,.4-6 Range, 2-34 Demand and Need for Infertility Services Among these 43 women, 9 had sought help for present infertility, and 7 for infertility in the past. Thus, the estimated demand for infertility services at the primary care level is 6 of 53 (0.4) (confidence interval ± 4.9) of all married or cohabiting women. If 0.4 may be expected to seek help for infertility during their reproductive lifetime, then the annual demand would be 0.4 divided by the number of between 20 and 44 = 24, 0.4/24 (0.43). For a Health District such as Sheffield with approximately 92,400 women in this age group, of whom 89.6 are ever married or cohabiting by age 44, this would represent a demand of 92,400 X 89.6 X 0.43 = 356 new cases per annum, requesting help at the primary care level (confidence limits± 66), based on the actual level of consultation reported in the questionnaire. If all couples who experienced infertility at some stage during the woman's 24-year reproductive life span, from age 20 to age 44, were to consult their family doctors, that is 28 of all married or cohabiting couples; for a Health District such as Sheffield this would be 28 X X = 966 consultations per annum The fact that the estimated need is greater than the demand suggests that either there is considerable unmet need, or that infertile couples do not invariably wish for medical help. Some couples will be referred earlier than others, by their family doctor, for various reasons such as advancing age (e.g., over 35 ) or facets of the infertility history or examination that might suggest that the problem can only be dealt with by specialist intervention. The need for infertility services at a specialist level may be based on the experience of infertility of a duration of 2 or more. Among those preg- Table 3 Prevalence of Secondary Infertility, Feelings About Pregnancy, Duration of Infertility, Whether Medical Help was Sought and Mean Age at Starting to Attempt to Conceive Among Women Who Had Been Pregnant Before Feelings about onset pregnancy No. of women Mean duration of infertility No. who sought medical help Mean age of women at starting to try to conceive Wish to become pregnant 3 Do not mind if I become pregnant Would prefer not to become pregnant 5 Other reasons Range, Range, Range, Range, Range, Total 6.9 Range, Range, Page Prevalence and incidence of infertility Fertility and Sterility

5 nant before, 4 took longer than 2 to conceive. Among those infertile now who have not been pregnant before, 7 had infertility of more than 2 ' duration. Thus, the expectation of infertility of more than 2 ' duration is estimated to be 2 of 53 (3. 7) (confidence limits± 5.5) among married or cohabiting couples. If 3.7 of all couples may expect to experience such infertility at some stage in their reproductive lives, then the annual need for specialist referral of infertile patients over the 24-year span from 20 to 44 used in this survey, would be 3.7 of 24 = 0.57 of all married or cohabiting couples, which in Sheffield would be 924,000 X 89.6 X 0.57 = 4 72 specialist referrals per annum. Women's Wishes About Becoming Pregnant Not all of the women not using birth control expressed a desire to become pregnant. This can be seen in Tables 2 and 3. Those with primary infertility differed from those with secondary infertility in the distribution of their reasons for not using birth control. Those who had no previous pregnancies (Table 2) included four who wished to become pregnant, with a mean duration of infertility of 3.6 (range,.4 to 6 ) and three who stated "I do not mind if I become pregnant," with a mean duration of infertility of 0.3 (range, 5 to 6 ). The age range of both groups at the onset of their attempts to conceive was similar, 23 to 34 for those who wished to become pregnant, and 2 to 32 for those who "did not mind." None stated that they would prefer not to become pregnant, and two gave "other reasons" that would indicate that they had made adjustments to their inability to conceive. Among those with secondary infertility (Table 3), only three stated that they wished to become pregnant, and one that she "did not mind," whereas five stated that they would "prefer not to become pregnant, but were prepared to take the risk." Two of these five women had in fact consulted a doctor about difficulty in becoming pregnant. Some women, especially those who already have a child, may be happy to "risk" further pregnancy but might not necessarily wish to seek advice or treatment if no pregnancy ensues. Others, who experience difficulty in conceiving, may after a time cease to wish to become pregnant and organize their lives so that they may prefer not to. By this time, the perceived risk of becoming pregnant is almost nil. These factors may in part explain the discrepancy between "apparent need" and "demand." Acceptability DISCUSSION The study indicates that a questionnaire designed to ascertain incidence and prevalence of infertility can be widely acceptable. The nonresponse of 8 of those who were mailed the questionnaire may be due either to women having left their former addresses, and therefore not receiving the questionnaire, or to a refusal to respond. A total of five questionnaires were returned marked "not known at this address." It is likely that many more than this were undelivered. It has been shown that general practitioner age/sex registers contain an error of 0 of people who have in fact left. 7 The main reason for refusal to respond is likely to be apathy. One woman made known her unwillingness to take part. There is no way of knowing whether the questionnaire was unacceptable to any other nonresponders. However, the 82 response rate is similar to that obtained in other surveys to the general public on issues that are thought to be less sensitive. Comprehensibility Apart from the misunderstanding about whether or not sterilization was to be included as "birth control," the answers to the questions were internally consistent, suggesting that the questionnaire had been well understood. The question that was misunderstood must be reworded before any further use of the questionnaire. The temptation to expand the questionnaire in order to gain more information should be resisted. Sufficient information can be obtained from the questionnaire as it stands (with the above-mentioned alteration), to estimate incidence, prevalence, and duration of primary and secondary infertility, the rate of recruitment to pregnancy for first pregnancies and for "previous pregnancies" that may or may not have been first pregnancies, and to estimate demand and need for infertility services. Prevalence and Incidence of Infertility The estimates of prevalence and incidence of infertility are based on the assumption that married or cohabiting couples do engage in sexual intercourse. It was thought that the inclusion of direct Vol. 5, No.4, April989 Page Prevalence and incidence of infertility 575

6 Table4 All Present Cases of Infertility Feelings about No. of No. who sought pregnancy women medical help Wish to become pregnant 7 4 Do not mind if I become pregnant 4 Would prefer not to become pregnant 5 2 Other reason 4 2 Total 20 9 questions about sexual activity would increase the length and complexity of the questionnaire, and might also be unacceptable to some women. The opportunity for women to state that they did not engage in sexual activity was there, in the question relating to reason for non-use of birth control: one woman did state that she and her husband are "not sexually inclined." This woman was not counted as part of the numerator. Although not at risk of pregnancy, she does, however, form part of the population that is defined as the denominator. Rates of incidence and prevalence are usually based on large populations among which many individuals are at little or no risk. Confidence Limits and Sample Size The small numbers of infertile women in this survey mean that the estimates given here have wide confidence limits. The confidence limits given for prevalence and incidence calculated from this small pilot study indicate that considerably larger numbers would be required to produce figures within sufficiently small confidence limits to be useful for planning. In order to reduce the confidence limits, it is necessary to increase the size of the sample. The effect of increasing the sample size in order to obtain 2,000 adequate replies was examined. The total sample size initially sent the questionnaire would then be 2,000 X 250/53 = 3,268. The number of cases of primary infertility then would be expected to be 9 X 2,000/53 = 8, a prevalence of 5.9, with a confidence interval ±.. It would be possible to reduce the number of questionnaires sent out if the sampling frame could be drawn up to include only married or cohabiting women. However, general practitioners do notalways have this information on their age-sex registers. It also may be useful to stratify the numbers in each age group so that the age structure of the sample accurately represents the age structure of women in the planning population, such as the Health District. In this way, the external validity of the survey would be increased. Demand and Need for Infertility Services This pilot study suggests that infertility, as defined, is a common experience. The questionnaire provides information about the duration of infertility among those who eventually became pregnant, including those who are pregnant now, and among those who are still not pregnant. The information given may be inaccurate because of the difficulty of remembering the duration of non-use of contraception. This inaccuracy is likely to be greater among those who experienced no difficulty in becoming pregnant, and among those who were pregnant some time ago. If a sufficiently large sample is used, many women will be "pregnant now" and therefore perhaps able to give more accurate information based on recent experience. In addition, it will be possible to distinguish between time taken to conceive first and subsequent pregnancies. Miscarriage A question was included that would determine the incidence of clinically apparent miscarriage in the previous 2 months and whether a first or subsequent pregnancy was lost. No miscarriages were recorded among this sample. Only 5 women were pregnant at the time, and 2 had had a baby in the previous 2 months. One or two miscarriages might have been expected. 8 Women's Wishes About Becoming Pregnant For a woman who does not wish to become pregnant, the inability to conceive may be a positive Table 5 Comparison of Population of Chapel Green with that of Sheffield, and England and Wales Women aged 20 to44 Children under 5 One-parent families Unemployed Ethnic minorities Sheffield (population 547,82) value England and Wales (population 500,754,000) value Chapel Green (population 23,800) value Page Prevalence and incidence of infertility Fertility and Sterility

7 advantage, unless it is associated with pathologic changes that induce symptoms or have other sequelae. Each couple must balance their own perceptions of the pros and cons of each type of birth control available to them against their perceptions of the likelihood that pregnancy might ensue if no birth control were used, (taking into account their age, frequency of intercourse, ability to recognize and abstain during the fertile period, and their previous conception times) and their feelings about a pregnancy, should it occur. Thus, non-use of contraception cannot be equated with a desire to become pregnant. Of 20 infertile couples in the survey, only 7 wished to become pregnant (of whom 4 had sought medical advice), while 4 "did not mind," of whom had sought medical advice. Five would "prefer not," although 2 of them had sought medical advice, and 4 gave "other reasons"- couple was "not sexually inclined," 2 of them had sought medical help, and the fourth was sure it was not possible to conceive (Table 4). It would appear that after a long period of attempting to conceive, women cease to make the emotional investment signified by "I wish to become pregnant" and retreat to a position of not minding one way or the other, and later become adjusted so that a pregnancy would perhaps be unwelcome. The availability of a new method of treatment might stimulate some of these women to "try again," so it might be a mistake to base the provision of services on estimates taken only from those who state a firm wish to become pregnant. Women or Couples? The questionnaire was sent to women, although the questions on it could have applied to each couple receiving it. The definitions of primary and secondary infertility refer to women: if a woman has been pregnant before but she and her present partner cannot achieve a pregnancy, then this is described as secondary infertility. The complications of a questionnaire that would elucidate whether ei- ther partner had achieved a pregnancy before with a different partner were felt to be prohibitive both in terms of acceptability and of comprehensibility. Applicability of results to other populations The pilot study was carried out in an area covering an electoral ward of Sheffield known as Chapel Green. Table 5 enables comparison of the population of Chapel Green with that of Sheffield as a whole, and England and Wales. Chapel Green is characterized by having more young families, fewer one-parent families, fewer unemployed, and fewer people of ethnic origin than would be expected in a population this size. The contrast with the rest of Sheffield is generally greater than with England and Wales as a whole. This suggests that the results from this small population might be more widely applicable to England and Wales as a whole, than to the population of Sheffield. REFERENCES. Leatherd A: District Health Authority Family Planning Services in England and Wales. London: London Family Planning Association, 985, p 2 2. Vessey MP, Wright NH, McPherson K, Wiggins P: Fertility after stopping different methods of contraception. Br Med J :265, Howe G, Westhoff C, Vessey M, Yeates D: Effects of age, cigarette smoking and other factors on fertility: findings in a large prospective study. Br Med J 290:697, Rachootin P, Oisen J: Prevalence and socioeconomic correlates of subfecundity and spontaneous abortion in Denmark. lnt J Epidemiol:245, Mosher WD, Pratt WF: Fecundity, infertility and reproductive health in the United States, 982. Vital and Health Statistics Series 23, No. 4. National Center for Health Statistics, Public Health Service. Washington, DC, US Government Printing Office, 987, Confidence Limits for Poisson Distribution. Geigy Scientific Tables, Vol. 2. Basle, Ciba Geigy, 982, p Fraser RC, Clayton DC: The accuracy of age/sex registers, practice medical records and family practitioner committee registers. J R Coli Gen Pract 3:40, Gustavii B: Chorionic biopsy and miscarriage in first trimester. (Letter) Lancet :526, 984 Vol. 5, No.4, April989 Page Prevalence and incidence of infertility 577