Article Vaginal gel versus intramuscular progesterone for luteal phase supplementation: a prospective randomized trial

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1 RBMOnline - Vol 16. No Reproductive BioMedicine Online; on web 21 January 2008 Article Vaginal gel versus intramuscular progesterone for luteal phase supplementation: a prospective randomized trial Luca Dal Prato studied medicine at the University of Bologna, Italy, and became MD in He completed his Obstetrics and Gynecology residency in the Department of Obstetrics and Gynecology of the University of Bologna in 1990, under Professor Carlo Flamigni. From 1990 to 1996 he worked as a postgraduate fellow at the Reproductive Medicine Unit of the University of Bologna. Since 1996 he has been working as physician at Tecnobios Procreazione, Centre for Reproductive Health in Bologna. He has carried out investigations in the use of GnRH agonists and gonadotrophins for ovarian stimulation in assisted reproduction treatments. Dr Luca Dal Prato Luca Dal Prato 1, Liana Bianchi 1, Monica Cattoli 1, Nicoletta Tarozzi 1, Carlo Flamigni 2, Andrea Borini 1,3 1 Tecnobios Procreazione, Centre for Reproductive Health, Via Dante 15, I-40125, Bologna, Italy; 2 University of Bologna, Bologna, Italy 3 Correspondence: Tecnobios Procreazione, Via Dante 15, I-40125, Bologna, Italy; Tel: ; Fax: ; borini@tecnobiosprocreazione.it Abstract The aim of this randomized study was to compare the efficacy of intramuscular progesterone (IMP) and progesterone in vaginal gel (VGP) at two different doses for luteal support in IVF. A total of 412 patients, aged between 28 and 37 years, were randomized into three groups. The day after oocyte retrieval each patient began supplementation with one of the following: IMP 50 mg daily (150 patients), VGP 90 mg once daily (143 patients), or VPG 90 mg twice daily (148 patients). No significant difference was found between the three groups in any of the endpoints. The rate of positive β-human chorionic gonadotrophin per transfer was 38.4% with IMP, 35.0% with VPG once daily and 43.1% with VPG twice daily. Clinical pregnancy rate per transfer and implantation rate were 32.6% and 19.6% with IMP, 26.3% and 16.4% with one dose of VGP, and 37.2% and 21.1% with two doses of VGP. Live birth rate per transfer was 26.1%, 23.4% and 29.9%, respectively. Progesterone vaginal gel can be successfully used as an alternative to intramuscular progesterone for luteal support in IVF. One daily dose appears sufficient to induce clinical pregnancies and live births at a rate comparable to intramuscular supplementation. Keywords: assisted reproduction treatments, IVF, luteal support, vaginal progesterone Introduction Various means of administration have been used to provide progesterone for luteal supplementation in IVF. The most common form has been intramuscular progesterone (IMP) in oil, usually 50 mg per day. Local pain has been frequently reported when this route is used and inflammatory reactions and cold abscesses may occur with prolonged use of the intramuscular route. Orally administered progesterone shows a relatively poor bioavailability and rapid liver inactivation. In contrast, vaginal progesterone is reported to provide a well-accepted and effective form of luteal support in women undergoing IVF or egg donation, despite the low circulating progesterone concentrations. This is a consequence of direct vagina-to-uterus transport called the first uterine pass effect (Miles et al., 1994). Good results have been reported with micronized progesterone capsules administered vaginally (Smitz et al., 1992; Borini et al., 1995, 1996; Lightman et al., 1999). Existing data about the effectiveness of vaginal gel progesterone (VGP) over IMP are conflicting: some authors claimed good efficacy for VGP, at least equivalent to IMP (Chantilis et al., 1999; Schoolcraft et al., 2000), but other studies reported significantly higher implantation and live birth rates with IMP administration (Damario et al., 1999; Propst et al., 2001). Moreover, there is no general consensus on the most effective daily dose of VGP in IVF. Studies in the oocyte donation model show that histological observations and pregnancy rates for the once-daily and twice-daily regimens were equivalent (Gibbons et al., 1998; Jobanputra et al., 1999), leading investigators to choose the once-daily regimen in IVF cycles. However no prospective randomized trials have been performed to date to confirm if this choice is really the best option for IVF/ intracytoplasmic sperm injection (ICSI) Published by Reproductive Healthcare Ltd, Duck End Farm, Dry Drayton, Cambridge CB3 8DB, UK

2 362 The aim of the present randomized study was to compare the efficacy of two different daily doses of vaginal gel progesterone and intramuscular progesterone for luteal support in IVF or ICSI treatments. Materials and methods Protocol Between September 2001 and March 2004 a total of 456 women undergoing IVF or ICSI were enrolled in the trial. The study was approved by the authors institutional review board. The main inclusion criteria were: aged between 28 and 37 years at the time of enrolment; regular ovulatory menstrual cycles of days; infertility caused by tubal, idiopathic or male factors (with the exclusion of patients with cryptozoospermia requiring testicular sperm aspiration) or grade I II endometriosis; no more than three previous embryo transfers. Patients with grade III IV endometriosis, polycystic ovary syndrome, previous ovarian surgery, FSH levels >15 IU/l on day 3 of the menstrual cycle, or who had a previous poor or hyperresponse to gonadotrophins were excluded from the study. Eligible patients who agreed to participate were randomized into three treatment groups. Ovarian stimulation was performed with depot leuprorelin (Enantone 3.75; Takeda, Rome, Italy) in a long luteal protocol. At the onset of menses patients began gonadotrophin stimulation as described elsewhere (Dal Prato et al., 2001). Briefly, they received 4 ampoules (300 IU) per day of recombinant human FSH (r-hfsh) (follitropin a, Gonal F 75; Serono, Rome, Italy) for 2 days and 2 ampoules (150 IU) per day for 4 days. The dose was then adjusted according to individual response as assessed by 17β-oestradiol assay and ultrasound scanning performed every other day. Human chorionic gonadotrophin (HCG; Profasi HP, Serono, Rome, Italy), 10,000 IU, was administered when at least three follicles reached a maximum diameter of 20 mm, of which at least one was >23 mm. Cycles in which fewer than three follicles developed were discontinued. Transvaginal oocyte retrieval was performed under ultrasound guidance 36 h after HCG administration. The day after oocyte retrieval each patient began supplementation either with IMP (Prontogest; AMSA, Rome, Italy), 50 mg daily (group 1), or VGP (Crinone 8% ; Serono, Rome, Italy), 90 mg once daily (group 2) or 90 mg twice daily (morning and evening, every 12 h) (group 3). Two days after oocyte retrieval, a maximum of two embryos in women <35 years old and three embryos in women >35 years old were replaced in the uterine cavity via the transcervical route. Supplementation continued until a pregnancy test was performed 15 days after embryo transfer and, in case of pregnancy, until sonographic confirmation of embryonic viability (about days after embryo transfer). Clinical pregnancy was defined as the presence of one or more gestational sacs detected on ultrasound scan performed at least 4 weeks after embryo transfer. Biochemical pregnancy loss was defined as a rise of β-hcg with no further evidence of the gestational sac on an ultrasound scan. Miscarriage was defined as pregnancy loss after ultrasound confirmation of embryo implantation and before 12 weeks. Live birth was defined as the delivery of one or more live babies; twins and triplets were considered as one live birth in this analysis. Parameters evaluated The primary endpoint, chosen according to previous studies (Damario et al., 1999), was the number of patients with a positive β-hcg test (>5 IU/l). This endpoint was considered a good marker of endometrial receptivity, since it is less influenced by embryo viability and genetic factors than clinical pregnancy and implantation rate. The following secondary endpoints were also recorded: the number of clinical pregnancies, miscarriages, pregnancies >12 weeks and deliveries (live births) and implantation rate. To evaluate the consistency between groups, evaluation was also made of: number of FSH ampoules; number of days of stimulation; 17β-oestradiol and number of follicles at HCG administration; total number of oocytes retrieved and mature oocytes; fertilization rate; and number of cleaved and transferred embryos. Plasma progesterone assays were not performed, because the direct vagina-to-uterus transport of vaginally administered progesterone makes this measurement irrelevant (Schoolcraft et al., 2000). Sample size The primary endpoint of the study was the proportion of biochemical pregnancies. A two-tailed test was used. Starting from an expected proportion of 40% in the selected cohort of infertile patients, the sample size for each group was estimated to be adequate for verifying the equivalence among the compared therapies. The considered range of equivalence around expected biochemical pregnancy was 10% (i.e. from 30% to 50%), assuming an alpha of 0.05 and a power of 0.8. Based on these parameters, a minimal sample size of 135 patients was estimated for each branch. Assignment Assignment to the different groups occurred on the day after oocyte retrieval, after assessment of oocyte fertilization. The randomization list was provided by an external statistician and the treatment sequence given to the investigator using sealed envelopes containing the name of one of the three medications (Prontogest, Crinone once daily, Crinone twice daily). Dark envelopes were used so their content could not be seen against bright light. Each envelope and allocation was sequentially numbered to prevent patients from being randomized out of sequence. Envelopes were not allowed to be opened in advance and were opened only by a nurse not involved in the trial. No blinding procedure was planned for this study due to the complex management of the blinding procedures with two different routes of administration: one intramuscular versus a single or double endovaginal. Statistical analysis Analysis was performed on an intention to treat (ITT) basis (all patients included in the study). Data are presented as mean ± SD or frequency. To compare clinical baseline parameters among groups, the one-way analysis of variance (ANOVA) was used. Post-hoc comparisons were performed by a Duncan test, only

3 when the f value was statistically significant. With regard to clinical outcomes, the H-test of Kruskal-Wallis was performed to compare the proportion between the three groups, while the z-test (Kolmogorv-Smirnov) was used to compare the proportion of the occurrence of outcome in paired groups. To compare the implantation rate among groups, the chi-squared test was used. A P-value under 0.05 was considered statistically significant. Results Participant flow and follow-up A total of 456 women were found to be eligible for the protocol and started ovarian stimulation. Of these, 441 underwent oocyte retrieval. In all, 412 patients had oocytes fertilized and were therefore randomized: 138 into group 1 (IMP), 137 into group 2 (VGP once daily), 137 into group 3 (VGP twice daily). All the 412 randomized patients underwent embryo transfer and completed the study. Figure 1 shows the participant flow and follow-up. IVF was performed in 61 patients in group 1, in 68 patients in group 2 and in 66 patients in group 3, whereas ICSI was carried out in 77 patients in group 1, in 69 patients in group 2 and in 71 patients in group 3. The three groups were homogenous for age, characteristics of ovarian stimulation and number of transferred embryos (Table 1). No statistically significant difference was found between the three groups in any of the analysed endpoints, except in the number of follicles on day of HCG, which were significantly higher in group 3 than in group 2 (P = 0.003) (Duncan Test post hoc). This difference does not influence the outcome of the study, since there was no difference in the number and quality of the oocytes and of the transferred embryos. The clinical results are shown in Table 2. With regard to the primary endpoint of the study, there was no significant difference among groups in the proportion of biochemical pregnancies, ranging from 35.0% (relative to the VGP once daily group) and 43.1% (relative to VGP twice daily group). Furthermore, the observed values of biochemical pregnancy were near the expected value. Figure 1. Participant flow through the trial. IM = intramuscular; VG = vaginal gel. 363

4 Table 1. Comparison of the cycle parameters of the study groups. Parameter Progesterone administration Intramuscular Vaginal gel Vaginal gel once daily twice daily No. of cycles (ITT) No. of IVF-ET/ICSI cycles 61/77 68/69 66/71 Age (years) 33.1 ± ± ± 3.4 No. of FSH ampoules 41.9 ± ± ± 21.5 Oestradiol on HCG day (pg/ml) 1666 ± ± ± 868 No. days of stimulation 11.7 ± ± ± 1.5 No. of follicles 16.9 ± ± 6.6 a 18.4 ± 7.3 a No. of oocytes 14.4 ± ± ± 7.7 No. of mature oocytes 9.4 ± ± ± 5.5 No. of inseminated oocytes 11.2 ± ± ± 4.7 No. of fertilized oocytes 7.9 ± ± ± 3.6 No. of embryos 7.6 ± ± ± 3.7 No. of transferred embryos 2.1 ± ± ± 0.5 Values are mean ± SD unless otherwise stated; HCG = human chorionic gonadotrophin; ICSI = intracytoplasmic sperm injection; ITT = intention to treat; IVF-ET = IVF and embryo transfer. a P = (Duncan test, post hoc). There were no other significant differences between the three study groups. Table 2. Comparison of the clinical outcomes in the study groups. Outcome Progesterone administration Intramuscular Vaginal gel Vaginal gel once daily twice daily No. of ITT cycles (ET) Positive HCG (%/transfer) 53 (38.4) 48 (35.0) 59 (43.1) Biochemical pregnancy loss (%/HCG+) 8 (15.1) 12 (25.0) 8 (13.6) Clinical pregnancies (%/transfer) 45 (32.6) 36 (26.3) 51 (37.2) Miscarriages (%/clinical pregnancy) 6 (13.3) 4 (11.1) 9 (17.6) Implantation rate (%) 58/296 (19.6) 49/299 (16.4) 64/304 (21.1) Ectopics (%/clinical pregnancy) 1 (2.2) 0 0 Pregnancies >12 weeks (%/transfer) 38 (27.5) 32 (23.4) 42 (30.7) Live births (%/transfer) 36 (26.1) 32 (23.4) 41 (29.9) There were no significant differences between the three study groups (Kruskal-Wallis H-test). ET = embryo transfer; HCG = human chorionic gonadotrophin; ITT = intention to treat. 364 No statistically significant difference was found between the three groups in any of the secondary endpoints (Table 2). The rate of biochemical pregnancy loss was 15.1% in the women treated with IMP, 25.0% in those treated with one dose of VGP and 13.6% in those treated with two doses of VGP, therefore the clinical pregnancy rate per transfer and implantation rate were 32.6% and 19.6% with IMP, 26.3% and 16.4% with one dose of VGP, 37.2% and 21.0% with two doses of VGP. The miscarriage rate was 13.3%, 11.1% and 17.6%, respectively. The rate of pregnancy >12 weeks was 27.5%, 23.4% and 30.7%, respectively. Finally, live birth rate per transfer was 26.1%, 23.4% and 29.9%, respectively. Discussion Vaginal progesterone is reported to provide a well accepted form of luteal support in women undergoing IVF. Some of the advantages of the transvaginal route are: avoidance of local pain in the site of injection; avoidance of first pass hepatic metabolism; rapid absorption; lack of undesirable side effects (e.g. a hypnotic effect); relatively high bioavailability. The most important advantage, however, is the local endometrial effect, known as uterine first-pass effect (Miles et al., 1994). Due to the direct vagina-to-uterus transport, high endometrial progesterone concentrations may be achieved (Bulletti et al.,

5 1997), despite low circulating progesterone levels (Cicinelli et al., 2000). Previous studies on oocyte donation showed no difference in terms of pregnancy and implantation rates between patients using progesterone in oil versus vaginal micronized progesterone (Borini et al., 1995, 1996). Crinone 8% (Serono, Rome, Italy) is a vaginal gel containing 90 mg micronized progesterone in an oil-in-water emulsion on a polycarbophil base, providing a controlled and sustained release of the drug through the vaginal wall over 24 h (Bulletti et al., 1997). This drug has been used for luteal support in donor egg cycles in women with no ovarian function. The efficacy of either a 90 mg single daily dose (Jobanputra et al., 1999) or 90 mg twice daily (Gibbons et al., 1998) was found to be similar to 100 mg daily intramuscular progesterone in terms of pregnancy rate. Moreover, endometrial biopsy performed in a mock cycle showed an in phase endometrium with both doses, with no correlation between endometrial development and serum progesterone concentration. The results of these in-vitro studies in the oocyte donation model induced investigators to choose the once-daily regimen in IVF cycles. A number of studies have been performed in recent years to investigate the efficacy of vaginal progesterone gel in patients undergoing IVF, but the results are conflicting. A retrospective study (Damario et al., 1999) showed lower clinical pregnancy and embryonic implantation rates and higher biochemical pregnancy rates, when vaginal progesterone gel rather than intramuscular progesterone is used for luteal phase support after IVF embryo transfer. Another report (Schoolcraft et al., 2000) comparing a series of 43 patients treated with vaginal gel progesterone with historical controls treated with intramuscular progesterone, and with the data reported by the Society for Assisted Reproduction Therapy, showed comparable clinical pregnancy and live birth rates with the two regimens. Furthermore excellent acceptability and preference was reported for the vaginal gel. There are still few prospective, randomized studies comparing vaginal progesterone gel and intramuscular progesterone. A recent meta-analysis has reviewed ten studies comparing vaginal administration (as cream, in micronized form, as pessaries, as sustained release gel, or as a vaginal ring) with intramuscular administration of progesterone in cycles with gonadotrophin-releasing hormone agonists (GnRHa) (Daya and Gunby, 2004). The 18% decrease in the odds of clinical pregnancy with vaginal progesterone did not quite reach statistical significance, but the decreases observed for ongoing pregnancy (27%) and live birth (59%) were statistically significant. No significant difference was observed in the rates of miscarriage or multiple pregnancy. From this meta-analysis there is not yet sufficient evidence to conclude that the vaginal route of progesterone administration is not as efficacious as the intramuscular route. Moreover, there is no evidence of a difference in efficacy between vaginal progesterone gel and other types of progesterone administered vaginally. An open-label study (Propst et al., 2001) randomized 201 women undergoing IVF to supplementation with VGP (Crinone 8%; 90 mg once daily) or IMP (50 mg once daily) beginning the day after oocyte retrieval. Once-a-day progesterone supplementation with VGP resulted in significantly lower embryo implantation, clinical pregnancy, and live birth rates compared with women supplemented with intramuscular progesterone. It has been suggested (Damario et al., 1999; Propst et al., 2001) that the cause of reduced embryo implantation after vaginal progesterone gel may just be the enhanced local effect on the endometrium induced by the first uterine pass, that results in significantly higher endometrial progesterone concentrations compared with intramuscular administration (Cicinelli et al., 2000). The final effect may be premature endometrial advancement and untimely closure of the implantation window. A study evaluating mid-luteal biopsies from oocyte donors undergoing ovarian stimulation and from oocyte recipients, both treated with VGP (Crinone 8%), showed an endometrial advancement of about 2 days in the former group compared with the latter (Kolb and Paulson, 1997). Alternatively, the once-daily regimen may be inadequate for luteal support after IVF or ICSI. In a prospective randomized trial, the interim analysis of which has recently been published (Yanushpolsky et al., 2007), VGP (Crinone 8%) was administered 24 h later than intramuscular progesterone, to compensate for the possible advancement in endometrial maturation. A similar efficacy with respect to pregnancy, implantation and miscarriage rates for patients receiving VGP once daily or IMP was reported. In the present trial, no significant differences were found in the rates of positive β-hcg, clinical pregnancy or live birth between either single or double vaginal doses and intramuscular progesterone. Moreover there were no significant differences in the above parameters between the single- and double-dose groups. These data confirm the results reported by Yanushpolsky et al. (2007), although in the present study luteal supplementation was started on the same day (i.e. 1 day after oocyte retrieval) in each treatment group. Vaginal administration seems to provide proper uterine impregnation of progesterone, enough to assure adequate luteal support in patients undergoing IVF or ICSI procedures, after stimulation with a long luteal GnRH-agonist plus recombinant-fsh protocol. The present study shows that VGP adds no significant advantage in terms of clinical outcome when compared with intramuscular administration, but it does not impair embryo implantation, as reported in other studies (Damario et al., 1999; Propst et al., 2001). Therefore, it may be used as a good alternative to intramuscular progesterone. Kleinstein (2005) reported the use vaginal progesterone capsules (Utrogest 200) compared with vaginal progesterone gel (Crinone 8%) for luteal phase support during assisted reproduction and found no difference in outcome and tolerability. As far as is known, this is the first prospective randomized trial that compares the efficacy of two different daily doses of vaginal gel progesterone with that of intramuscular progesterone. No evidence was found that twice-daily administrations provide a better outcome than a single administration. The once-daily regimen seems to be enough for luteal support in IVF or ICSI treatments. These findings are in agreement with a recent study (Geber et al., 2007) showing no significant difference in pregnancy rate between once-daily vaginal gel progesterone and vaginal capsules three times daily. The pregnancy rate reported by that trial was higher compared with the present study and with other studies in the literature (44% with vaginal gel and 36% with vaginal capsules), but the number of embryos transferred was also higher. 365

6 366 Since the safety and good acceptability of vaginal progesterone gel has already been well documented by a number of trials (Schoolcraft et al., 2000; Kleinstein, 2005; Yanushpolsky et al., 2007), patient compliance was not included in the endpoints of the present study. No important adverse events or side-effects were reported by patients in any of the treatment groups. In one prospective study, which compares the results of VGP (90 mg of Crinone 8%) with historical controls treated with 50 mg IMP (Chantilis et al., 1999), positive β-hcg and implantation rates were similar when vaginal or intramuscular support was given during the luteal phase in IVF-embryo transfer cycles, despite lower serum progesterone concentrations. There were, however, higher rates of biochemical pregnancy loss and early vaginal bleeding (11 13 days after oocyte retrieval) with VGP. On the other hand, women who received intramuscular progesterone had more gestational sacs without a fetal heartbeat, resulting in a similar ongoing pregnancy rate between the two groups. This finding seems to suggest that intramuscular progesterone differs from vaginal progesterone only in the prolongation of the presence of non-viable gestational sacs. The present study, however, does not confirm this conclusion, since it found no significant differences in the live birth rate between IMP and either VGP doses, but biochemical pregnancy losses and clinical pregnancy losses are equally distributed among the three treatment groups. This may suggest that, provided a proper uterine impregnation of progesterone has been achieved, the route of administration and the dose have no influence either in the incidence or in the time of occurrence of pregnancy loss, which are probably mainly influenced by the characteristics of the embryos. An observation that has been reported by the majority of studies is the earlier bleeding pattern of patients treated with vaginal progesterone (either in micronized or in gel form) compared with intramuscular progesterone (Chantilis et al., 1999; Roman et al., 2000; Propst et al., 2001). Although the onset of bleeding in patients who had a negative β-hcg test was not included as one of the endpoints of the study, the authors evaluated this feature in a subgroup of patients for whom the data were available (180 women) and found an incidence of bleeding before the β-hcg test which was similar in the two VGP groups (71.6% in single dose and 64.1% in double dose), but significantly (P < 0.001) higher than in the IMP group (32.7%). This trial confirms previously published studies, in which early bleeding took place mainly in non-pregnant women (Chantilis et al., 1999). Therefore it concurs with the conclusion that bleeding reflects the lack of a viable pregnancy rather than inadequacy of luteal support (Penzias and Alper, 2003). The hypothesis of advanced endometrial maturation made by some authors (Propst et al., 2001) may actually explain this early bleeding pattern. On the other hand, the present study shows that the cause of early bleeding cannot be inadequate luteal support provided by once-daily administration of VPG, since either single or twice-daily doses display a similar bleeding pattern. In conclusion, this randomized study shows that vaginal gel can be successfully used as an alternative to intramuscular progesterone in luteal support in assisted reproduction techniques. One daily dose appears sufficient to induce a number of pregnancies and live births comparable to intramuscular supplementation, despite the higher incidence of early bleeding in non-pregnant patients, as already reported in the literature. Doubling the daily dose of VGP neither improves the final outcome of assisted reproduction treatment significantly, nor reduces early bleeding in non-pregnant women. Declaration The study was completely at the investigators cost. None of the authors has any conflict of interest with this study or received consulting fees, honoraria or research support from any pharmaceutical manufacturer. The patients who participated in this trial did not receive any compensation or free products or services as an inducement to participate. References Borini A, Bianchi L, Violini F et al Oocyte donation program: pregnancy and implantation rates in women of different ages sharing oocytes from single donor. Fertility and Sterility 65, Borini A, Violini F, Bianchi L et al Improvement of pregnancy and implantation rates in cyclic women undergoing oocyte donation after long-term down-regulation. 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7 Miles RA, Paulson RJ, Lobo RA et al Pharmacokinetics and endometrial tissue levels of progesterone after administration by intramuscular and vaginal routes: a comparative study. Fertility and Sterility 62, Penzias AS, Alper MM 2003 Luteal support with vaginal micronized progesterone gel in assisted reproduction. Reproductive BioMedicine Online 6, Propst AM, Hill JA, Ginsburg ES et al A randomized study comparing Crinone 8% and intramuscular progesterone supplementation in in vitro fertilization-embryo transfer cycles. Fertility and Sterility 76, 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, Schoolcraft WB, Hesla JS, Gee MJ 2000 Experience with progesterone gel for luteal support in a highly successful IVF programme. Human Reproduction 15, 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, 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. Epub ahead of print: 15 June 2007 (PMID: ). Received 24 September 2007; refereed 9 October 2007; accepted 9 November