Article Progesterone supplementation during cryopreserved embryo transfer cycles: efficacy and convenience of two vaginal formulations

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1 RBMOnline - Vol 17. No Reproductive BioMedicine Online; on web 16 July 2008 Article Progesterone supplementation during cryopreserved embryo transfer cycles: efficacy and convenience of two vaginal formulations Dr Vuong Thi Ngoc Lan received her MD degree in 1996, and her Master s Degree in Clinical Embryology at the National University of Singapore in During the past 10 years, she worked as clinical director of the largest IVF centre in Vietnam, which has up to 2000 IVF cycles per year. Currently she works in the Department of Obstetrics and Gynecology, University of Medicine of Ho Chi Minh city, and is now PhD fellow in Reproductive Medicine. Dr Lan has been an invited speaker at regional and international meetings. Her primary interests are luteal phase support, use of antagonist in IVF, ovulation induction in PCOS patients and IVM. Dr Vuong Thi Ngoc Lan VTN Lan 1,5, PH Tuan 2, LT Canh 3, HM Tuong 2, CM Howles 4 1 Department of Infertility, Tu Du Obstetrics and Gynecology Hospital, Ho Chi Minh City, Vietnam and Department of Obstetrics and Gynecology, University of Medicine of Ho Chi Minh City, Vietnam; 2 IVF Van Hanh, Van Hanh Hospital, Ho Chi Minh City, Vietnam. 3 Department of Infertility, Tu Du Obstetrics and Gynecology Hospital, Ho Chi Minh City, Vietnam. 4 Merck Serono International SA, 9 Chemin des Mines, Geneva, 1211, Switzerland 5 Correspondence: Tel: ; Fax: ; lanvuong@hcm.fpt.vn Abstract Sequential exogenous oestradiol and progesterone are often used to prepare the endometrium in frozen embryo transfer (FET) cycles. This open-label, randomized study compared the efficacy and acceptability of self-administered once daily vaginal progesterone gel and vaginal micronized progesterone tablets (three times daily) for luteal support in FET cycles. An Asian population of women (aged 45 years) were assigned randomly to receive progesterone gel (90 mg, once daily, n = 100) or vaginal micronized progesterone tablets (200 mg, three times daily, n = 100). All received oestradiol from day 2 of the menstrual cycle, for at least 10 days (or until endometrial thickness was 8 mm), before self-administering progesterone for 2 days before FET and up to 14 weeks afterwards if pregnancy occurred. Clinical pregnancy rates (31% for gel and 28% for tablets) and implantation rates (9.8% and 8.8%, respectively) were not significantly different between the treatment groups. Asian women using once daily progesterone gel found the gel easy to use and comfortable, and preferred it to their previous experience of vaginally administered tablets. In summary, once-daily vaginal progesterone gel has similar efficacy to vaginal tablets and is associated with high patient satisfaction. Keywords: frozen embryo transfer, luteal support, vaginal micronized progesterone gel, vaginal micronized progesterone tablet Introduction 318 Success or failure of an IVF or intracytoplasmic sperm injection (ICSI) cycle depends on several factors, most importantly embryo quality and uterine receptivity. When a high-quality embryo is transferred during a fresh or frozen cycle, success depends on the interaction between the mother and embryo in the peri-implantation period (Emiliani et al., 2005). During this period the endometrium is histologically transformed into an environment suitable for the implantation and development of the embryo. This short window of embryo implantation is regulated by oestradiol and progesterone (de Ziegler et al. 1994; Punyadeera et al., 2003). Frozen embryo transfer (FET) can be carried out in a regular ovulatory cycle. To ensure a receptive uterine environment, the transfer must be timed with ovulation. Assessing this optimal time for frozen thawed embryo replacement may require an intervention such as serial measurement of LH levels, and may also involve ultrasound assessment of ovarian activity. Such monitoring can be inconvenient and stressful for the patient, and the subsequent timing of embryo replacement may be equally inconvenient for the fertility centre. An approach used by an increasing number of centres, which does not depend on a regular ovulatory cycle, is the use of exogenous steroid 2008 Published by Reproductive Healthcare Ltd, Duck End Farm, Dry Drayton, Cambridge CB3 8DB, UK

2 hormones to prepare the endometrium for implantation. Steroid replacement regimens were first proposed by Lutjen et al. (1985) in order to allow donated gametes to be transferred to women who had complete ovarian failure. Subsequently, de Ziegler et al. (1991) and Lelaidier et al. (1992) reported the use of a similar regimen in women with functioning ovaries. Additionally, such steroid replacement regimens can be used to time embryo replacement more precisely and hence allow clinic and embryological staff to programme treatment cycles. Finally, a satisfactory endometrial thickness can be achieved by this method, only minimal monitoring of these cycles is required (Banz et al., 2002). Oestradiol is used during the first half of the cycle, and subsequently combined with progesterone from around day 15, or according to assessment of endometrial proliferation (Bals-Pratsch et al., 1999). Since the introduction of these steroid replacement regimens, the duration of progesterone administration prior to embryo transfer has varied. In the literature, the thawed 4 8-cell embryo has been transferred 2 5 days after starting progesterone treatment (Nawroth and Ludwig, 2005). Other guidelines suggest that transfer should take place days after starting oestradiol/ progesterone treatment, depending on the type of embryo being transferred (Toner, 2004). Progesterone can be given via an oral, intramuscular or vaginal route; however, the efficacy, safety and tolerability of exogenous progesterone depends on the route of administration (Ludwig and Diedrich, 2001). Compared with intramuscular or vaginal administration, oral administration has been associated with significantly lower rates of implantation and pregnancy (Friedler, 1999; Licciardi et al., 1999) and a higher incidence of side effects (Pouly et al., 1996). Intramuscular injection of progesterone suspended in oil achieves circulating concentrations of progesterone that may be above the physiological range, and is associated with normal endometrial development and good rates of pregnancy (Smitz et al., 1992). Intramuscular injections, however, require administration by a healthcare professional and are uncomfortable and can lead to potentially serious adverse effects, including injury to the sciatic nerve and abscesses at the injection site (Ludwig and Diedrich, 2001). For these reasons, in Vietnam, progesterone in oil for intramuscular injection is rarely used in a clinical setting. The vaginal route is at least as effective as intramuscular administration, and offers a number of advantages in terms of direct action on the endometrium ( first uterine pass effect, Bulletti et al., 1997) and convenience and tolerability (Smitz et al., 1992; Tavaniotou et al., 2000; Ludwig and Diedrich, 2001; Penzias, 2002; Penzias and Alpers, 2003; Yanushpolsky et al., 2007; Zarutskie and Phillipsa, 2007). Administering progesterone as a vaginal suppository or tablet can require application at least three times a day, and can be messy and inconvenient for the woman. Progesterone gel, administered once or twice daily, has been shown to have similar efficacy as micronized vaginal progesterone tablets or capsules given three times a day in fresh-cycle IVF/ICSI (Kleinstein, 2005; Geber et al., 2007; Simunic et al., 2007). In such cycles, however, endogenous progesterone levels are highly elevated because of multiple corpora lutea. A more appropriate model for examining the efficacy and safety of vaginally administered progesterone would be one where only exogenous steroid replacement is applied. Additionally, all the studies referred to above were carried out in women of Caucasian descent. To the authors knowledge, there has only been one study carried out in a relatively small Chinese patient population (n = 60) comparing vaginally administered progesterone gel versus progesterone pessary for luteal phase support following gonadotrophin stimulation for IVF (Ng et al., 2003). There have not been any studies in an Asian population undergoing steroid replacement for example in oocyte recipient or frozen embryo replacement cycles. The current study, therefore, aimed to compare the efficacy and convenience of progesterone gel with vaginal micronized progesterone in a cohort of Asian women given steroid replacement as part of an FET cycle. Materials and methods Study design This was an open-label, randomized trial that compared the efficacy of progesterone gel and vaginal micronized progesterone tablets for luteal support in an FET cycle. The study was conducted at the Department of Infertility, Tu Du Obstetrics and Gynecology Hospital, Ho Chi Minh City, Vietnam and patient recruitment was limited to the period from April to August Women undergoing FET cycles were randomly allocated using a blocked randomization method (block size of four) prior to the time of starting progesterone. The study protocol was approved by the local review committee. Study population Women aged 45 years were eligible for inclusion in the study if they had no contraindications to pregnancy, and had at least three good quality cleavage stage (4 6 cells) embryos frozen and stored in the embryo bank of Tu Du Hospital. These patients received oestradiol for at least 10 days and endometrial thickness was 8 mm. All frozen embryos were generated from the unit s standard ovarian stimulation protocol that utilized recombinant human FSH (rhfsh) in combination with a gonadotrophin-releasing hormone antagonist. In each straw, 3 4 embryos were frozen. Embryo quality after thawing was defined, based on the criteria of Veeck (1999). Embryos were assigned a score for the number and regularity of blastomeres and the degree of fragmentation as proposed by Veeck (1999). Exclusion criteria included a history of more than three previous IVF attempts, and uterine abnormalities that could compromise the implantation process (e.g. fibroids, endometrial polyp, bicornuate uterus, adhesion of uterine cavity). All patients gave informed consent to participate in the study. Interventions From day 2 of the cycle, all women received oral oestradiol (Progynova, Schering, Germany) for at least 10 days. The initial dosage was 2 mg administered four times daily, which was subsequently adjusted according to endometrial thickness (measured on ultrasound). When endometrial thickness was at least 8 mm, progesterone was added to this regimen. Patients were assigned randomly to receive vaginal progesterone gel (Crinone, Merck Serono International S.A., Geneva, Switzerland), 90 mg, self-administered once daily in the 319

3 morning. Patients were assigned randomly to receive vaginal micronized progesterone (Utrogestan, Besins International, France) as 200 mg tablets, self-administered three times daily. Two days after initiating progesterone treatment, embryos were thawed and transferred. The procedure for choosing the number of straws for thawing and assessing the quality of embryos for transfer was as follows. If a patient had more than one straw available, each straw was thawed consecutively, and as soon as one thawed embryo was graded good quality, no remaining straws were thawed. Embryos that had more than 50% surviving blastomeres were chosen for transfer. Those with 100% intact blastomeres were scored as being good quality embryos. From the day of embryo transfer, women continued to selfadminister both oral oestradiol at a reduced dose of 2 mg twice daily and progesterone until the results of a serum beta-human chorionic gonadotrophin (HCG) pregnancy test were obtained. All women were tested for pregnancy 14 days after embryo transfer using serum HCG concentration. If the result was positive, clinical pregnancy was confirmed on ultrasound by the presence of a gestational sac containing a viable fetus inside the uterus around 35 days after starting progesterone. If pregnancy was confirmed, vaginal progesterone was continued up to week 14 of pregnancy as well as oestradiol valerate 2 mg twice daily. To assess the convenience and comfort of applying progesterone gel, women in the gel treatment group were asked to complete a questionnaire by the time of the pregnancy test on day 14. Outcome measures The outcome measures included clinical pregnancy rate, length of the luteal phase in patients who were not pregnant, implantation rate and patient-assessed convenience. Implantation rate was defined as the total number of embryos implanting successfully, divided by the total number transferred per patient. Statistical analysis The outcomes of IVF treatment in patients who received luteal support with either vaginal progesterone gel or vaginal tablets were compared using Fisher s exact test. The acceptability and tolerance of both preparations were estimated using the chisquared test. Statistical significance was set at P < Results Patients Two hundred patients underwent randomization (100 patients each in the vaginal progesterone gel and vaginal progesterone tablet groups), and all started treatment. There were no significant differences between the treatment groups with regards to patient age or duration of infertility (Table 1). Women allocated to progesterone gel had undergone more previous IVF attempts than those allocated to vaginal progesterone tablets (1.5 ± 0.07 versus 1.2 ± 0.05, P = 0.02; Table 1). There were no significant differences between groups in the duration of oestradiol administration, endometrial thickness on the day of embryo transfer, or number of embryos transferred, however the mean number of good quality embryos was higher 1.8 ± 0.15 versus 1.3 ± 0.11 (P = 0.01) in the gel versus micronized tablet group (Table 2). Efficacy Clinical pregnancy rates (31% for progesterone gel and 28% for vaginal micronized progesterone) and implantation rates (9.8% for progesterone gel and 8.8% for vaginal micronized progesterone) were not significantly different between the treatment groups (Table 3). In view of the observed difference in the mean number of good quality embryos transferred, the pregnancy outcome data was analysed according to the embryo grading score. In cycles with at least one good quality embryo transferred versus those cycles with no embryo scored as good quality transferred and in cycles with at least two good quality embryos versus cycles with less than two, there were no differences in the pregnancy rates (data not shown). The mean (± SD) length of the luteal phase among patients who did not become pregnant was also not significantly different (15.4 ± 0.1 days in the progesterone gel group and 15.6 ± 0.08 days in the vaginal micronized progesterone group, P = 0.1 Table 1. Baseline characteristics of women undergoing frozen embryo transfer, using vaginal progesterone gel or vaginal progesterone tablets for luteal support. Progesterone gel Progesterone (n = 100) tablets (n = 100) P-value Age (years) a 33.3 ± ± 0.49 NS Age range (years) Median age (years) Duration of infertility (years) a 5.8 ± ± 0.26 NS Range Median duration of infertility (years) 6 6 Number of IVF attempts a 1.5 ± ± Range Median NS = not statistically significant. a Mean ± SEM.

4 Table 2. Characteristics of frozen embryo transfer cycles, using vaginal progesterone gel or vaginal progesterone tablets for luteal support. Progesterone Progesterone P-value gel (n = 100) tablets (n = 100) Endometrial thickness on day of embryo transfer (mm) 10.8 ± ± 0.14 NS Duration of oestradiol only administration (days) 14.7 ± ± 0.32 NS Mean number of embryos thawed 4.0 ± ± 0.12 NS Number of embryos transferred 3.9 ± ± 0.10 NS Number of good-quality embryos transferred 1.8 ± ± NS = not statistically significant. Values are mean ± SEM. Table 3. Pregnancy outcomes, including positive pregnancy test, following frozen embryo transfer, using vaginal progesterone gel or vaginal progesterone tablets for luteal support. Progesterone Progesterone gel (n = 100) tablets (n = 100) Positive blood HCG test (n) 33 (33) 34 (34) Clinical pregnancy rate (n) 31 (31) 28 (28) Biochemical pregnancy a (n) 2 (2) 5 (5) Ectopic pregnancy (n) 0 (0) 1 (1) Implantation rate b (%) Values in parentheses are percentages. There were no statistically significant differences between the two groups. HCG = human chorionic gonadotrophin. a Pregnancy confirmed by blood HCG test. b Embryos implanted per patient/embryos transferred. by t-test). There were no incidences of very premature early bleeding in either group. Convenience All 100 women who had received progesterone gel completed the questionnaire (100% response rate). Of these, 91 (91%) had previous experience of using vaginal micronized progesterone. In total, 95 patients stated that progesterone gel was easy or very easy to use, 94 stated that it was hygienic or very hygienic to use, 95 reported that it was comfortable to use, and 98 described it as convenient to use. Regarding their overall experience with the product, 96 women evaluated progesterone gel as excellent or good. When women who were assigned to progesterone gel were asked to recall their previous experience of using vaginal micronized progesterone, the most common comments pertained to leakage of the product, poor hygiene and the time-consuming nature of the application procedure for the tablets (data not shown). Of the 91 patients assigned to progesterone gel who had prior experience of using micronized progesterone, most felt that the sustained-release gel was quicker (93.4%; n = 85), easier (94.5%; n = 86), more comfortable (95.6%; n = 87) and less messy (95.6%; n = 87) to use than micronized progesterone. Most patients expressed a preference for the sustained-release formulation (93.4%; n = 85). Discussion To the authors knowledge, this randomized, open-label study is the first to indicate that there is no significant difference in clinical pregnancy and implantation rates among Asian women undergoing FET who had used micronized progesterone gel applied vaginally, compared with those who had used vaginal progesterone tablets. Whilst there were significantly more good quality embryos (1.8 ± 0.15 versus 1.3 ± 0.11) transferred in the gel versus tablet group, further stratification of the data set according to the number of good quality embryos transferred, did not show any differences in the pregnancy outcomes. Whilst embryo grading is a useful tool in assessing embryo quality, the ultimate outcome of pregnancy is determinant on multiple factors including endometrial receptivity (for review see Guzeloglu-Kayisli et al., 2007) and also for instance whether embryo transfer was carried out under ultrasound guidance (Ali et al., 2008). In the authors unit it is not routine policy to utilize ultrasound-guided embryo transfer in FET cycles. Notwithstanding the above caveat, these results agree with those from previous studies that have shown similar pregnancy and implantation rates with vaginal progesterone gel compared with vaginal progesterone tablet/capsules in Caucasian women with endogenous progesterone production (Kleinstein, 2005; Geber 321

5 322 et al., 2007; Simunic, 2007) or compared with intramuscularly administered progesterone in women using donor eggs (Gibbons et al., 1998; Jobanputra et al., 1999). In women who did not have a positive pregnancy test, there were no incidences of premature early bleeding prior to discontinuation of progesterone supplementation. A previous study reported a higher incidence of early bleeding, due to the lack of a viable pregnancy, in women using vaginal compared with intramuscularly administered progesterone following IVF FET, with bleeding occurring in 42% of cycles with vaginal progesterone and in 27% with intramuscular progesterone (Yanushpolsky et al., 2007). This difference did not, however, translate into any difference in ongoing pregnancy rates between the vaginal (47.6%) and intramuscular (46.3%) progesterone groups. The higher rates of premature bleeding following IVF could be attributed to the vastly different luteal oestradiol levels between stimulated cycles with multiple corpora lutea, and the combined steroid hormone replacement protocol used in the present study for luteal support (Roman et al., 2000; Aktan et al., 2004). In a meta-analysis by Pritts and Atwood (2002), the authors concluded that implantation rates might be improved through the use of oral oestradiol supplementation to vaginal or intramuscular progesterone. More recently, Lukaszuk et al. (2005) reported significantly (P < 0.001) higher ongoing clinical pregnancy rates in women undergoing IVF who had received supplementary oestradiol and vaginal progesterone in the luteal phase, compared with women who had received only progesterone. Although this area requires further investigation, these findings suggest that the addition of oestradiol may be an important consideration in cycles that use vaginal progesterone for luteal support. A recent re-analysis has challenged the findings from the Cochrane meta-analysis of vaginal and intramuscular progesterone that reported a non-significant advantage for intramuscular progesterone in terms of ongoing pregnancy and live births (Daya and Gunby, 2004). Zarutskie and Phillipsa (2007), whose analysis omitted a study in which vaginal progesterone was under-dosed and included a later study of vaginal progesterone use, have shown a reduced miscarriage rate in patients treated with vaginal compared with intramuscular progesterone. This may be due to a greater bioavailability of progesterone in the uterus following vaginal delivery, because of the first uterine pass effect (Bulletti et al., 1997; Ludwig and Diedrich, 2001). The use of vaginal progesterone has also been shown to reduce uterine contractions among women at risk of threatened abortion. In a prospective, randomized, double-blinded study by Palagiano et al. (2004), vaginal progesterone or placebo was administered once a day for 5 days after the diagnosis of threatened abortion. The addition of vaginal progesterone was effective in reducing both pain and the frequency of uterine contractions after 5 days (P < versus placebo). Furthermore, the incidence of spontaneous abortion was significantly lower in the active treatment group (P < 0.05). Women in the present study preferred progesterone gel to vaginal progesterone tablets. The majority found progesterone gel to be convenient, easy to use, less time consuming, and cleaner to use, owing to no leakage. These results support previous findings with progesterone tablets (Ludwig and Diedrich, 2001; Penzias and Alper, 2003), vaginal capsules (Ludwig et al., 2002) and vaginal suppositories (Ng et al., 2003). Leakage and messiness are complaints commonly associated with the use of vaginal micronized progesterone, and are a consequence of the oil base of the product melting. Leakage is less common with progesterone gel because of the bioadhesive properties of polycarbophil and the small volume of gel used. The time required for application is also a concern for the user. Women who receive vaginal progesterone tablets, which are taken three times daily, are advised to lie down immediately following insertion in order to prevent expulsion. This regimen contrasts with the requirements for progesterone gel, which is applied once daily and does not require the patient to lie down after application. Indeed the latter advantage will probably increase compliance among patients. Conclusion There was no significant difference in clinical pregnancy and implantation rates in Asian women undergoing FET who used micronized progesterone gel (90 mg once daily) applied vaginally and those who used vaginal progesterone tablets (200 mg three times daily). Asian patients preferred the progesterone gel to vaginal progesterone tablet formulation, as it was more convenient and easier to use. Acknowledgements The authors would like to thank Dr Polly Field (supported by Merck Serono International S.A.) and Dr Eleni Stavridi (Merck Serono International S.A.) for help with manuscript preparation. References Aktan E, Bozkurt K, Ozer D et al The effect of mid-luteal estradiol level on the outcome of ICSI-ET cycles. Archives of Gynecology and Obstetrics 269, Ali C, Khashan AS, Horne G et al Implantation, clinical pregnancy and miscarriage rates after introduction of ultrasoundguided embryo transfer Reproductive BioMedicine Online 17, Bals-Pratsch M, Al-Hasani S, Schopper B et al A simple, inexpensive and effective artificial cycle with exogenous transdermal oestradiol and vaginal progesterone for the transfer of cryopreserved pronucleated human oocytes in women with normal cycles. Human Reproduction 14 (Suppl. 1), Banz C, Katalinic A, Al-Hasani S et al Preparation of cycles for cryopreservation transfers using estradiol patches and Crinone 8% vaginal gel is effective and does not need any monitoring. European Journal of Obstetrics, Gynecology, and Reproductive Biology 103, Bulletti C, de Ziegler D, Flamigni C et al Targeted drug delivery in gynaecology: the first uterine pass effect. Human Reproduction 5, Daya S, Gunby J 2004 Luteal phase support in assisted reproduction cycles. Cochrane Database of Systematic Reviews, CD de Ziegler D, Fanchin R, Massonneau M et al Hormonal control of endometrial receptivity. The egg donation model and controlled ovarian hyperstimulation. Annals New York Academy of Science 734, de Ziegler D, Cornel C, Bergeron C et al Controlled preparation of the endometrium with exogenous estradiol and progesterone

6 in women having functioning ovaries. Fertility and Sterility 56, Emiliani S, Delbaere A, Devreker F et al Embryo-maternal interactive factors regulating the implantation process: implications in assisted reproductive. Reproductive BioMedicine Online 10, Friedler S, Raziel A, Schachter M et al Luteal support with micronized progesterone following in-vitro fertilization using a down-regulation protocol with gonadotrophin-releasing hormone agonist: a comparative study between vaginal and oral administration. Human Reproduction 14, Geber S, Moreira AC, de Paula SO et al Comparison between two forms of vaginally administered progesterone for luteal phase support in assisted reproduction cycles. Reproductive BioMedicine Online 14, Gibbons WE, Toner JP, Hamacher P et al Experience with a novel vaginal progesterone preparation in a donor oocyte program. Fertility and Sterility 69, Guzeloglu-Kayisli O, Basar M, Arici A 2007 Basic aspects of implantation. Reproductive BioMedicine Online 15, Jobanputra K, Toner JP, Denoncourt R, Gibbons WE 1999 Crinone 8% (90 mg) given once daily for progesterone replacement therapy in donor egg cycles. Fertility and Sterility 72, Kleinstein J 2005 Efficacy and tolerability of vaginal progesterone capsules (Utrogest 200) compared with progesterone gel (Crinone 8%) for luteal phase support during assisted reproduction. Fertility and Sterility 83, Lelaidier C, de Ziegler D, Gaetano J et al Controlled preparation of the endometrium with exogenous oestradiol and progesterone: a novel regimen not using a gonadotrophin-releasing hormone agonist. Human Reproduction 10, Licciardi FL, Kwiatkowski A, Noyes NL et al Oral versus intramuscular progesterone for in vitro fertilization: a prospective randomized study. Fertility and Sterility 71, Ludwig M, Diedrich K 2001 Evaluation of an optimal luteal phase support protocol in IVF. Acta Obstetricia et Gynecologica Scandinavica 80, Ludwig M, Schwartz P, Babahan B et al Luteal phase support using either Crinone 8% or Utrogest: results of a prospective, randomized study. European Journal of Obstetrics, Gynecology, and Reproductive Biology 103, Lukaszuk K, Liss J, Lukaszuk M et al Optimization of estradiol supplementation during the luteal phase improves the pregnancy rate in women undergoing in vitro fertilization-embryo transfer cycles. Fertility and Sterility 83, Lutjen PJ, Leeton JF, Findlay JK 1985 Oocyte and embryo donation in IVF programmes. Clinical Obstetrics and Gynecology 12, Nawroth F, Ludwig M 2005 What is the ideal duration of progesterone supplementation before the transfer of cryopreservedthawed embryos in estrogen/progesterone replacement protocols? Human Reproduction 20, Ng EH, Miao B, Cheung W et al A randomised comparison of side effects and patient inconvenience of two vaginal progesterone formulations used for luteal support in in vitro fertilisation cycles. European Journal of Obstetrics, Gynecology, and Reproductive Biology 111, Palagiano A, Bulletti C, Pace MC et al Effects of vaginal progesterone on pain and uterine contractility in patients with threatened abortion before twelve weeks of pregnancy. Annals of the New York Academy of Sciences 1034, Penzias AS 2002 Luteal phase support. Fertility and Sterility 77, Penzias AS, Alper MM 2003 Luteal support with vaginal micronized progesterone gel in assisted reproduction. Reproductive BioMedicine Online 6, Pouly JL, Bassil S, Frydman R et al Luteal support after in-vitro fertilization: Crinone 8%, a sustained release vaginal progesterone gel, versus Utrogestan, an oral micronized progesterone. Human Reproduction 11, Pritts EA, Atwood AK 2002 Luteal phase support in infertility treatment: a meta-analysis of the randomized trials. Human Reproduction 17, Punyadeera C, Verbost P, Groothuis P 2003 Oestrogen and progestin responses in human endometrium. Journal of Steroid Biochemistry and Molecular Biology 84, Roman E, Aytoz A, Smitz JE et al Analysis of the bleeding pattern in assisted reproduction cycles with luteal phase supplementation using vaginal micronized progesterone. Human Reproduction 15, Simunic V, Tomic V, Tomic J et al Comparative study of the efficacy and tolerability of two vaginal progesterone formulations, Crinone 8% gel and Utrogestan capsules, used for luteal support. Fertility and Sterility 87, Smitz J, Devroey P, Faguer B et al A prospective randomized comparison of intramuscular or intravaginal natural progesterone as a luteal phase and early pregnancy supplement. Human Reproduction 7, Tavaniotou A, Smitz J, Bourgain C et al Comparison between different routes of progesterone administration as luteal phase support in infertility treatments. Human Reproduction Update 6, Toner P 2004 The luteal phase: luteal phase support protocols In: Gardner D, Weissman A, Howles C et al. (eds) Textbook of Assisted Reproductive Techniques: Laboratory and Clinical Perspectives. Taylor and Francis, London, pp Veeck L 1999 An Atlas of Human Gametes and Conceptuses: An Illustrated Reference for Assisted Reproductive Technology. Parthenon Publishers, New York. Yanushpolsky E, Hurwitz S, Greenberg L et al Comparison of Crinone 8% intravaginal gel and intramuscular progesterone supplementation for in vitro fertilization/embryo transfer in women under age 40: interim analysis of a prospective randomized trial. Fertility and Sterility. Jun 15, Epub ahead of print. Zarutskie PW, Phillipsa JA 2007 Re-analysis of vaginal progesterone as luteal phase support (LPS) in assisted reproduction (ART) cycles. Fertility and Sterility 88, S113. Declaration: The authors report no financial or commercial conflicts of interest. Received 22 November 2007; refereed 8 January 2008; accepted 17 April