GnRH antagonist in assisted reproduction: will it replace the agonist?

• Comment by   David R. Meldrum

• Comment by   Ehab Kelada & Ian Craft

• Comment by: A. Tavaniotou &  P. Devroey

 Comment by   David R. Meldrum, M.D.

California - U.S.A.

GnRH antagonists have three inherent advantages over GnRH agonists for AR cycles. First, by avoiding the agonist phase of gonadotropin release, development of cysts and prolonged rises of circulating estrogen with an associated delay of stimulation do not occur. Second, the duration of GnRH analog therapy is shortened since it is used only during the latter stage of follicular maturation. Finally and most importantly, the phase of marked hypoestrogenism before the onset of stimulation is avoided.

GnRH agonists have provided many advantages for assisted reproduction. It is important to have a detailed understanding of these benefits and their assumed mechanisms so that we can evaluate and optimize GnRH antagonist protocols to achieve equivalent outcomes.

Improved ovarian response

GnRH agonists increase ovarian response, providing more embryos and greater selection for fresh transfer, more frozen embryos and thus higher success with frozen embryo transfer, and a lower rate of cancellation for poor response. Since endogenous gonadotropins are lower at the beginning of stimulation, this improved response probably occurs through suppression of ovarian androgens (1). Various studies with GnRH antagonists have yielded ovarian responses slightly lower than with GnRH agonist in spite of higher endogenous gonadotropins at the start of stimulation in the antagonist group (2). This lower response is probably because ovarian androgens would be higher in the absence of any GnRH analog suppression.

Oral contraceptive (O.C.) pretreatment suppresses ovarian androgens and augments subsequent response to stimulation (3). Addition of O.C. pretreatment would be expected to improve stimulation response in GnRH antagonist cycles and to narrow the difference observed in the number of oocytes retrieved between antagonist and agonist regimens. By varying the duration of O.C. therapy, the flexibility in timing oocyte retrieval, otherwise lost with use of antagonist, will be restored. However, timing of stimulation relative to the last O.C. pill must be carefully considered, varies with age (gonadotropins recover more slowly in women over age 35) and presumably varies with the particular preparation. In one older study when stimulation was begun on the third morning after O.C., the stimulation (only two amps of hMG) was blunted in the subgroup whose FSH had not yet recovered from suppression. A detailed study of desogestrel 0.15 mg/ethinyl estradiol 0.03 mg suggests that the evening of day 4 after O.C. would be optimal in normal younger women (4), with stimulation delayed until day 5 or 6 for women over age 35 (5) or for poor responders.

Improved pregnancy outcome

GnRH agonists were reported in a meta-analysis to result in a two-fold increase of the pregnancy rate, although most of the difference was noted in those studies in which the control group was taking clomiphene citrate/hMG (probably because of the anti-estrogen effect of clomiphene). The benefit over hMG alone occurs by avoiding excessive exposure of LH to the developing follicles and by the improved ovarian response and improved embryo selection. The benefit of a relative suppression of LH was clearly shown in a dose-finding study of the antagonist, ganirelix (6). As the dose was increased progressively to 250 micrograms daily, LH levels fell and implantation rates increased. In the various studies comparing outcomes with antagonist and agonist, pregnancy rates have been about 5% lower. Although not statistically significant, this has been a consistent observation suggesting that ultimately a meta-analysis will confirm this minor difference. This may be in part due to fewer embryos and therefore less selection, and in part due to more variable control of LH secretion during follicle growth. Since high doses of antagonist were associated with lower implantation of fresh but not frozen embryos (6,7) and GnRH antagonists may have an anti-mitogenic effect on the endometrium, a direct inhibitory effect of antagonist on implantation cannot be ruled out.

Ideal control of LH secretion with antagonist during follicle maturation has not been achieved as yet. The antagonist must be started early enough in the course of stimulation to prevent premature increases of LH, but late enough so as to not increase gonadotropin requirements by excessive suppression of endogenous gonadotropins. Based on preliminary findings we suggest ultrasound scanning on day 5 of stimulation and to initiate ganirelix when the leading follicle has a mean diameter of 1.2 cm. On the other hand, when antagonist has been started, LH suppression can be profound in some women. In a large multicenter study of ganirelix at 250 ug daily compared to full dose leuprolide acetate, the mean level of LH in both groups on the day of hCG was 1.7 mIU/ml. However, with ganirelix, LH drops to about 25% of baseline after each dose and slowly recovers. Also, considering that the bioactive level of LH on antagonist is reduced by about 50%, the levels of LH in many patients are very low. In a study in monkeys receiving antide, a potent GnRH antagonist, addition of Rec LH to Rec FSH decreased the time of blastocyst formation and improved cryosurvival. In an uncontrolled study we have observed a higher blastocyst implantation rate with FSH/hMG than with pure FSH alone in women on full dose leuprolide acetate. These studies suggest that very low circulating LH may compromise optimal embryo development. We therefore suggest the substitution of one or two ampules of hMG for Rec FSH when ganirelix is begun.

With GnRH agonists the secretion of endogenous gonadotropins is fairly constant during stimulation whereas FSH and LH secretion will fall when antagonist is started. Clinicians accustomed to using a step-down approach to stimulation should be aware that antagonist therapy itself causes a step-down of circulating gonadotropins and should keep the dose more constant. Otherwise, decreases of estradiol may occur.

If at the 250 ug dose of ganirelix there is any residual inhibitory effect on implantation (250 ug is 1/8 to ½ of the doses where this was apparent), a greater rise of estradiol could counteract such an effect. Addition of hMG as outlined above, and avoiding a marked step-down of exogenous gonadotropins will increase estradiol secretion toward what is observed with GnRH agonist. Since O.C. pretreatment blocks the LH surge during subsequent stimulation, it is also possible that a lower antagonist dose could be considered.

In summary, minor differences in ovarian response to stimulation and of implantation have been observed with GnRH antagonist compared with GnRH agonists with a fixed protocol of stimulation using pure FSH. Pretreatment with O.C., individualization of the timing of antagonist treatment and administration of some exogenous LH are likely to erase these minor differences making GnRH antagonist the preferred regimen for AR in the future.

REFERENCES

1.        Cedars MI, Surrey E, Hamilton P, Meldrum DR. Leuprolide acetate lowers circulating bioactive luteinizing hormone and testosterone concentrations during ovarian stimulation for oocyte retrieval. Fertil Steril 1990;53:627-31

2.        Borm G, Mannaerts B, and the European Orgalutran Study Group. Treatment with the gonadotropin-releasing hormone antagonist ganirelix in women undergoing ovarian stimulation with recombinant follicle stimulating hormone is effective, safe and convenient: results of a controlled, randomized, multicenter trial. Hum Reprod 2000;15:1490-98

3.        Bijan MM, Mahutte NG, Dean N, Hemmings R, Bissonnette F, Tan SL. Effects of pretreatment with an oral contraceptive on the time required to achieve pituitary suppression with gonadotropin-releasing hormone analogues and on subsequent implantation and pregnancy rates. Fertil Steril 1998;70:1063-9

4.        Van Heudsen AM, Fauser BCJM. Activity of the pituitary-ovarian axis in the pill-free interval during use of low-dose combined oral contraceptive. Contraception 1999;59:237-43

5.        Fitzgerald C, Elstein M, Spona J. Effect of age on the response of the hypothalamo-pituitary-ovarian axis to a combined oral contraceptive. Fertil Steril 1999;71:1079-84

6.        The ganirelix dose-finding study group. A double-blind, randomized, dose-finding study to assess the efficacy of the gonadotropin-releasing hormone antagonist ganirelix (Org 37462) to prevent premature luteinizing hormone surges in women undergoing ovarian stimulation with recombinant follicle stimulating hormone (Puregon). Hum Reprod 1998;13:3023-31

7.        Kol S, Lightman A, Hillensjo T, Devroey P, Fauser B, Tarlatzis B, Mannaerts B, Itskovitz-Eldor J. High doses of gonadotropin-releasing hormone antagonist in in-vitro fertilization cycles do not adversely affect the outcome of subsequent freeze-thaw cycles. Hum Reprod 1999;14:2242-4

David R. Meldrum, M.D.

California, U.S.A.

Comment by   Ehab Kelada

Ian Craft

London, UK

A premature LH surge has been responsible for ovulation occurring prior to plan egg recovery and cancellation of many IVF cycles when using gonadotrophins alone, or combined with clomiphene citrate. Apart from premature ovulation, it negatively affects the outcome, due to lower oocyte and embryo quality.

The development of GnRH agonists made it possible to prevent this unfortunate event through selective medical hypophysectomy. The LHRH (GnRH) was isolated from hypothalamic extracts and its decapeptide amino acid sequence was established in 1971.

Among the different protocols using the GnRH agonists, the “long protocol” is generally the most effective and is the most often used at present. However, the “long protocol” has the disadvantages of a long treatment period until desensitisation occurs, as well as relatively high cost due to an increased requirement of gonadotrophins.

Although the concentration of hypothalamic GnRH in the systemic circulation is considered to be too low to interact with the extra pituitary GnRH receptors, it is important to appreciate that the amount of GnRH agonists used in assisted reproduction may lead to high levels that can have a significant effect on extra pituitary GnRH receptors. The use of a GnRH agonist is known to be associated with an increased risk of ovarian hyperstimulation syndrome (OHSS) and its sequelae, especially in patients with polycystic ovaries (PCO). On the other hand, a poor response, in some patients may be partially attributed to the GnRH agonist having a direct suppressing effect on the ovaries via GnRH receptors. The finding of GnRH receptors in the human ovaries lends support to our opinion. Actually, some the known techniques to improve the ovarian response in poor responders are to reduce the dose of GnRH agonist (micro-dose), or to stop it once down regulation is achieved, or even to avoid it completely. The goal is to avoid the complexities and costs of prolonged pharmaceutically driven treatments, to reduce the risk of over responders and improve the outcome of poor responders.

For twenty years, scientists have been trying to synthesize GnRH antagonists. The early generations of GnRH antagonists were not suitable for clinical use because of allergic side effects caused by histamine release. These compounds are far more complex than GnRH agonist with modification in the molecular structure at positions 1,2,3 & 8 in addition to those at position 6 & 10 seen in GnRH agonist. The new generations of GnRH antagonists: Cetrorelix (Cetrotide; Asta Medica AG, Frankfurt, Germany) and Garnirelix (Orgalutran; NV Organon, Oss, the Neherlands) are safe for clinical use. While the agonists act on chronic administration through the down regulation of receptors and desensitisation of the gonadotrophic cells, the antagonists bind competitively to the receptors and thereby prevent the endogenous GnRH from exerting its stimulatory effect on the pituitary cells avoiding any “flare-up” effect.

Cetrorelix was tested with a high dose (1 mg); when no LH surge occurred, the dose was decreased to 0.5 mg, 0.25 mg, and, finally. 0.1 mg. The minimal effective dose was 0.25 mg. For Garnirelix, doses ranging from 2 to 0.0625 mg were analysed simultaneously. A 0.25 mg/day of Garnirelix prevented an LH surge, and this dose was the minimal effective dose. Although the minimal effective dose was 0.25 mg for both drugs, no conclusion can be drawn for the similarity in clinical effectiveness. No studies comparing the two antagonists in combination with the same gonadotrophin stimulation regimen are available. When a daily dose of 0.25 mg is administered, the antagonist is given from approximately day 7 of the menstrual cycle onwards.

The advantage of administering a GnRH antagonist is the immediate decrease in the concentration of LH. Although the LH concentration can be controlled a few hours after the antagonist is administered, a flare-up occurs when the GnRH agonist is administered. Thus, it appears that, with the use of a GnRH antagonist, stimulation can begin on the first day of the menstrual cycle and that the treatment protocol is significantly shorter than that with the long GnRH agonist protocol.

The avoidance of GnRH agonists will reduce the duration and total amount of FSH and hence reduce the cost of treatment cycle. Furthermore, we have adopted the approach of using clomiphene citrate to reduce the cost of the treatment cycle even further. However, the best protocol to use is yet to be found through randomised clinical studies as to whether human menopausal gonadotrophin (HMG) or recombinant FSH would be best either alone or combined with clomiphene citrate. If HMG is used, the amount of circulating LH is not a concern. If, on the other hand, recombinant FSH is used, no exogenous LH is administered and a lack of LH is probable. However, from our data, there is no evidence that the use of recombinant FSH and GnRH antagonist has any adverse effect on the outcome.

It is not clear whether the process of oocyte maturation is similar if a GnRH agonist, rather than a GnRH antagonist, is used. There is evidence that with the long GnRH agonist protocol, oocyte development is more synchronised than when stimulation is started at the beginning of the menstrual cycle. However, when short, ultrashort, and long protocols were compared, the only significant difference convincingly shown was that the long protocol is preferred for practical reasons. However, the duration of the period of gonadotrophin suppression has not been proved to affect follicular recruitment and subsequent growth.

It has been documented that the injection of preovulatory hCG in GnRH agonist cycles initiates a significant decrease in LH during the early luteal phase. The same decrease in LH during the early Luteal phase has been observed in GnRH antagonist cycles. The exact mechanism behind this is as yet unknown. In theory, replacing hCG with recombinant LH will not prevent the luteal phase defect in agonist cycles. Replacing hCG with recombinant LH in antagonist cycles may, however, prevent a luteal defect with the possible avoidance of luteal support, which will reduce the risk of ovarian hyperstimulation.

We have assessed the use of Cetrorelix in conjunction with clomiphene citrate and gonadotrophin in 83 in-vitro fertilization (IVF) / gamete intrafallopian transfer (GIFT) cycles for 69 “difficult responders”. Difficult responders are defined as those patients who did not respond adequately to increasing doses of gonadotrophins (Poor responders), and those who showed an exaggerated response leading to OHSS (PCO patients).

Group I included 43 poor responders (54 cycles) with one live birth in 46 previous IVF cycles with GnRH agonists.

Group II included 26 patients (29 cycles) with polycystic ovaries. Twenty five previous IVF cycles with GnRH agonists had resulted in one live birth and four of these patients had developed ovarian hyperstimulation syndrome (OHSS).

The treatment protocol involved a daily dose of clomiphene citrate 100 mg for 5 days and gonadotrophin injections from cycle day 2. Cetrorelix 0.25 mg/day was started when the leading follicle reached 14 mm until the hCG administration. The outcome in both groups was favourable compared to the previous treatment with GnRH agonists.

In group I the abandoned cycle rate was 17 versus 39%. The number of oocytes retrieved was slightly higher in favor of GnRH antagonist (5.7 versus 5.1 oocyte/cycle) at a lower dose of follicle-stimulating hormone (FSH) (676 versus 921 IU/ oocyte). Also, the live birth / ongoing pregnancy rate was higher (11.1% versus 3.5%) in the antagonist group.

Group I: Outcome of cycles on the Cetrorelix-clomiphene citrate-gonadotrophin protocol as compared to that of previous cycles on LHRH analogue protocols in poor responders

In group II, fewer oocytes were produced (10 versus 14.3 oocytes/cycle), using a lower dose of gonadotrophin (156 versus 202 IU/oocyte). Also, the live birth / ongoing pregnancy rate was higher (29.6% versus 4.2%) in favour of the antagonist group. No patient experienced OHSS.

Group II: Outcome of cycles on the Cetrorelix-clomiphene citrate-gonadotrophin protocol as compared to that of previous cycles on LHRH analogue protocols in PCO

We are encouraged by the response of these groups of patients and acknowledge that those with a limited ovarian reserve (i.e. poor responders) may not benefit to the same degree as others who have responded poorly to LHRH analogue and gonadotrophin protocols because of an adverse effect of the analogue on the ovary and in whom one can expect a totally different response with antagonist use.

In group I, the success rate for poor responders with previous failed treatment is relatively good. In addition, the response to gonadotrophin stimulation with the antagonist improved compared to that with the agonist as evidenced by a reduced rate of cancelled cycles (16.6 versus 39.1%) and marginally improved oocyte production (5.7 versus 5.1 oocytes/cycle) with a lower FSH dosage (3864 versus 4769 IU/completed cycle and 676 versus 921 IU/oocyte retrieved). This may be due to the release of natural gonadotrophins, together with the stimulating effect of clomiphene citrate and lack of any direct inhibitory effect of GnRH agonist on the ovary. We are encouraged that this protocol will be appropriate for normal responders, including those who intend to donate eggs to help other women to achieve pregnancy. This benefit needs to be further clarified by studying the use of clomiphene citrate-gonadotrophin-cetrorelix protocol in normal responders, compared with that obtained with down-regulation using a GnRH agonist.

In group II, the patients with PCO produced fewer oocytes (10 versus 14.3 oocytes/cycle) using a lower dose of FSH (1565 versus 2903 IU/completed cycle and 156 versus 202 IU/oocyte) and none developed OHSS. The use of down regulation protocols with a GnRH agonist is known to be associated with an increased risk of OHSS, particularly in patients with PCO. However, we believe that the clomiphene citrate-gonadotrophin-cetrorelix protocol reduces this risk, as there is no down-regulation prior to ovarian stimulation and one is able to administer cautiously lower doses of gonadotrophins, either on an alternate day, or on a daily basis.

Our experience of using clomiphene citrate-gonadotrophin-cetrorelix for “difficult responders” suggests that this protocol may be of value for some patients who have not responded well to GnRH agonists and gonadotrophins. We predict that an improved response will occur in some, and the required amount of gonadotrophin injections will be reduced and hence the cost. We also believe that Cetrorelix reduces the risk of OHSS, since a lower dose of gonadotrophins may be found effective in stimulating a moderate number of follicles, rather than an excessive cohort, particularly in patients with PCO because of lower stimulation.

In conclusion, GnRH antagonist is a powerful suppressor of LH and FSH. Although its use is already standardized and is associated with a good pregnancy rate, more research is needed to achieve consistently good results. The other benefits require further evaluation include: the absence of flare, triggering of the surge by GnRH, absence of luteal support, and, above all, flexibility of use, allowing protocols with reduced doses of gonadotrophins and at lower cost.

Ehab Kelada and Ian Craft

London Gynaecology & Fertility Centre

London

UK

GnRH antagonist in assisted reproduction: will it replace the agonist?

Does the endometrium hide the answer?

Comment by: A. Tavaniotou, M.D.

                        P. Devroey, M.D., Ph.D.

Brussels, Belgium

It has been more than one decade since LHRH agonists have been the “golden standard” in assisted reproductive techniques. The key issue of using the LHRH agonists was the avoidance of the premature endogenous LH surge, that was a main drawback of HMG or CC/HMG stimulation, leading to a high percentage of cycle cancellations. LHRH agonists were used in the down regulation or “long” protocol and in the flare up or “short” protocol. The application of the long protocol is associated with a long duration of the treatment, with administration of a large number of ampoules, as well as with side effects and patients’ discomfort, due to the initial decrease of steroid concentrations to menopausal levels. Unfortunately, although the short protocol is by far more convenient for the patients, in a recent meta-analysis it has been proven to be less effective than the long protocol, as pregnancy rates were significantly lower after the short or ultrashort protocol than after the long (1).

The introduction of LHRH antagonists in daily practice, namely Cetrorelix (Asta Medica, Frankfurt, Germany) and Ganirelix (Organon, Oss, The Netherlands) have set up a new concept in assisted reproduction techniques. Antagonist administration is able to block effectively the endogenous LH surge, without compromising the follicular growth and recent phase II and phase III studies have shown their efficacy in in-vitro fertilization cycles (2-4).

A great advantage of the antagonist administration, compared to the agonist long protocol, is the convenience of this protocol for the women. Treatment duration is reduced to 14 days instead of 5 to 6 weeks and no side effects are known so far. Administration of the contraceptive pill in the cycle preceding the treatment may also assist in an even improved treatment schedule. However, compared to the agonist, in a phase III multi-centre study, significantly less cumulus-oocyte complexes were retrieved after Cetrorelix/HMG stimulation, than after buserelin/HMG (4). One possible explanation for this observation, is that in this multi-centre trial, the length of the treatment, the number of administered ampoules and the estradiol values on the day of hCG injection, were less in the antagonist group (4). However, it has to be underlined, that there was a significant reduction in ovarian hyperstimulation syndrome in the antagonist group.

Surprisingly enough, in all the published trials, comparing antagonists with the long agonist protocol (4-6), a lower implantation rate was consistently found in the antagonist group, although it never reached statistically significant differences. Up to now, no etiologic factor has been detected to explain this difference. In the dose-finding study of Ganirelix the implantation rates were adversely related with the dosage of the antagonist, and they were significantly decreased when higher doses of Ganirelix were used (7). There are two possible explanations for this finding: either antagonist treatment directly affects embryo quality or it affects endometrial receptivity. However, it has been also demonstrated, that the high doses of LHRH antagonist in in vitro fertilization cycles, did not adversely affect the outcome of the subsequent freeze-thaw cycles (8). This observation indicates, that there is no direct adverse effect of the LHRH antagonist on embryo quality. Accordingly, if embryo toxicity can be ruled out, the only answer might be given in terms of endometrial receptivity. As LHRH receptors have been detected on the endometrium (9), it is probable that that there is a direct negative effect on the endometrium after LHRH antagonist treatment. However, it is also possible, that the association of LHRH antagonists with human menopausal gonadotropins, i.e. the ovarian superovulation itself, adversely affects all the features of endometrial maturation (10).

It has been widely accepted, that luteal phase supplementation is needed after LHRH agonist treatment (11). The use of LHRH agonist per se was the reason for the luteal phase defect in this protocol. After LHRH agonist treatment, the pituitary is not responsive to endogenous GnRH stimulus and subsequently luteal phase supplementation is needed, either by means of hCG or progesterone (12).

On the contrary, as the pituitary is responsive to GnRH stimulus after antagonists (13), it was hypothesised, in the beginning of the dose-finding study with Cetrorelix, that there was no need for luteal phase supplementation. Surprisingly enough, four out of the first six patients treated in the phase II dose-finding study, and receiving no luteal phase supplementation, showed signs of a defective luteal phase, such as low mid-luteal progesterone concentrations, or shortened luteal phase length (14). This is the reason why in subsequent cycles, luteal phase were supplemented by means of a low dose of Human Chorionic Gonadotropin (1500IU).

The analysis of the endocrinological profiles of the luteal phases after Cetrorelix 0.25 or 0.5 in association with HMG showed that LH serum concentrations were unmeasurably low in the antagonist group (15). Recently, we were able to demonstrate that the endocrine behavior of LH during the early luteal phase after gonadotropin stimulation and injection of hCG was similar after antagonist/HMG as well as after HMG stimulation (Tavaniotou et al., submitted). In a recent trial (16) it was also clearly demonstrated in antagonist/rec FSH cycles, that, by starting the gonadotropin therapy later during the follicular phase, the luteal phase defect in terms of duration was not present and luteal phase length was normal. As the luteal phase defect occurred with LHRH antagonists, as well as with LHRH agonists, as well as with HMG only, it indicates that the use of the agonist or antagonist is not the key factor in this phenomenon. Luteal phase defect is the result of the current (HMG/HCG) protocols, used for ovarian superovulation, although a direct drug effect cannot be excluded.

In the future, several studies are needed to investigate whether luteal phase supplementation is needed in antagonist/HMG cycles and endometrium biopsies have to be performed in different stimulation protocols, in order to compare endometrial features.

Furthermore, as, theoretically, the antagonist gives us the possibility to replace the ovulatory hCG with LHRH agonist, this treatment may be considered as a future prospective in order to reduce the risk of hyperstimulation syndrome in assisted reproduction.

REFERENCES

1.        Daya S. Gonadotropin releasing hormone agonist protocols for pituitary desensitization in in vitro fertilization and gamete intrafallopian transfer cycles. Cohrane Database Syst Rev 2000; (2) CD001299.

2.        Albano C, Smitz J, Camus M, Riethmüller-Winzen H, Siebert-Weigel M, Diedrich K, et al. Hormonal profile during the follicular phase in cycles stimulated with a combination of human gonadotrophin and gonadotrophin-releasing hormone antagonist (Cetrorelix). Hum Reprod 1996; 11: 2114-8.

3.        Albano C, Smitz J, Camus M, Riethmüller-Winzen H, Van Steirteghem A, Devroey P. Comparison of different doses of gonadotropin-releasing hormone antagonist Cetrorelix during controlled ovarian hyperstimulation. Fertil Steril 1997; 67: 917-22.

4.        Albano C, Felberbaum RE, Smitz J, Riethmüller-Winzen H, Engel J, Diedrich K and Devroey P on behalf of the European Cetrorelix Study Group. Ovarian stimulation with HMG: results of a prospective randomized phase III European study comparing the luteinizing hormone-releasing hormone (LHRH) antagonist cetrorelix and the LHRH agonist buserelin. Hum Reprod 2000; 15: 526-31.

5.        Olivennes F, Belaisch-Allart J, Emperaire JC, Dechaud H, Alvarez S, Moreau L, et al. A prospective randomized controlled study in IVF-ET with a single dose of a LH-RH antagonist (Cetrorelix) or a depot formula of a LH-RH agonist (Triptorelin). Fertil Steril 2000; 73:314-20.

6.        Tarlatzis B. Clinical outcome of a multi-centre trial of Ganirelix (Orgalutran ^® ) in women undergoing controlled ovarian hyperstimulation. Gynecol Endocrinol 1999; 13 (Suppl 1): 13 (Abstract).

7.        The Ganirelix dose-finding study group. A double-blind, randomized, dose-finding study to assess the efficacy of the gonadotrophin-releasing hormone antagonist Ganirelix (Org 37462) to prevent premature luteinizing hormone surges in women undergoing ovarian stimulation with recombinant follicle stimulating hormone (Puregon). Hum Reprod 1998; 13: 3023-31.

8.        Kol S, Lightman A, Hillensjo T, Devroey P, Fauser B, Tarlatzis B et al. High doses of gonadotrophin-releasing hormone antagonist do not adversely affect the outcome of subsequent freeze-thaw cycles.

9.        Imai A., T. Ohno, et al., 1994. Presence of gonadotropin releasing hormone receptor and its messanger ribonucleic acid in endometrial carcinoma and endometrium. Gynecol. Oncol. 55, 144-148.

10.     Sterzik K, Dallenbach C, Schneider V, Sasse V, Dallenbach-Hellweg G. In vitro fertilization: the degree of endometrial insufficiency varies with the type of ovarian stimulation. Fertil Steril 1988; 50: 457-462.

11.     Smitz J, Devroey P, Camus M, Deschacht J, Khan I, Staessen C, et al. The luteal phase and early pregnancy after combined GnRH-agonist/HMG treatment for superovulation in IVF or GIFT. Hum Reprod 1988; 3, 5: 585-590.

12.     Smitz J, Erard P, Camus M, Devroey P, Tournaye H, Wisanto A et al. Pituitary gonadotrophin secretory capacity during the luteal phase in superovulation using GnRH-agonists and HMG in a desensitization or flare-up protocol. Hum Reprod 1992; 7: 1225-1229.

13.     Felberbaum R, Reissmann T, Küpker W, Bauer O, al Hasani S, Diedrich C et al. Preserved pituitary response under ovarian stimulation with HMG and GnRH antagonists (Cetrorelix) in women with tubal infertility. Eur J Obstet Gynecol Reprod Biol 1995; 61: 151-5.

14.     Albano C, Grimbizis G, Smitz J, Riethmüller-Winzen H, Reissmann T, Van Steirteghem A. et al. The luteal phase of nonsupplemented cycles after ovarian superovulation with human menopausal gonadotropin and the gonadotropin-releasing hormone antagonist Cetrorelix. Fertil Steril 1998; 70: 357-359.

15.     Albano C, Smitz J, Tournaye H, Riethmüller-Winzen H, Van Steirteghem A, Devroey P. Luteal phase and clinical outcome after human menopausal gonadotrophin/gonadotrophin releasing hormone antagonist treatment for ovarian stimulation in in-vitro fertilization /intracytoplasmic sperm injection cycles. Hum Reprod 1999; 14: 1426-1430.

16.     de Jong D., N. M. Macklon and B. C. J. M. Fauser. A pilot study involving minimal ovarian stimulation for in-vitro fertilization: extending the “follicle-stimulating hormone window” combined with the gonadortopin releasing hormone antagonist cetrorelix. Fertil Steril 2000; 73: 1051-4.

A. Tavaniotou, M.D.

P. Devroey, M.D., Ph.D.

Centre of Reproductive Medicine

Brussels,

Belgium

Under Permission Of MEFS Journal