GnRH antagonist in Ovarian stimulation for IVF/ET

Usama M. FoudaProfessor of Obstetrics and Gynecology , Faculty of medicine, Cairo University . Egypt

Introduction •Gn Rh is a decapeptide (10 amino acids) neurohormone that is secreated

by the hypothalamus in pulsatile pattern.

•GnRH stimulates the synthesis and secretion of the gonadotropins by the

pituitary gonadotopes. Low-frequency GnRH pulses lead to FSH release,

whereas high-frequency GnRH pulses stimulate LH release.

• A gonadotropin-releasing hormone analogue is a synthetic peptide drug

modelled after the human hypothalamic gonadotropin-releasing

hormone(GnRH).

• A GnRH analogue is designed to interact with the GnRH receptor and

modify the release of pituitary gonadotropins .

• Two types of analogues have to be distinguished;

Gn RH agonists

Gn RH antagonists

GnRH agonists cause initial stimulation of GnRH receptors (flare up )

followed by down-regulation of the pituitary GnRH receptors.

GnRH-antagonists cause immediate and dose-related inhibition of

gonadotropins release by competitive occupancy of the GnRH receptors in

the pituitary gland.

Structure of GnRH

1 2 43 65 98 107

pyro (Glu) – His – Trp – Ser – Tyr – Gly – Leu – Arg – Pro – Gly – NH2

activation of the GnRH receptor

regulation of GnRHreceptoraffinity

regulation ofbiologic activity

GnRH antagonists available in the market Cetrorelix (cetrotide , Serono ) and Ganirelix( Antagon , Organon ) .

Characteristics of GnRH antagonist

Ganirelix Fully effective

within 4 hours, with a half-life of about 13 hours

Cetrorelix Fully effective

within 8 hours, with a half-life of about 36 hours

Advantages of GnRH antagonist Immediate, reversible suppression of gonadotropin secretion which avoids

effects related to the initial flare up .

Endogenous inter-cycle FSH rise rather than FSH suppression, thus

resulting in a significant reduction in the effective dosage and shorter

treatment, than with GnRHa.

Lower incidence of OHSS.

In high risk cases for OHSS , Gn RH agonist can be used instead of HCG to

trigger ovulation .

Ideal regimen for patients with breast cancer undergoing controlled

ovarian stimulation , due to decreased risk of post-trigger oestradiol

exposure as well as OHSS risk.

Ideal regimen for cancer patients undergoing controlled ovarian

stimulation and gametes or embryo cryopreservation prior to

gonadotoxic therapy , because of the avoidance of an acute

stimulation of endogenous gonadotropins and the short duration of

treatment .

Disadvantages of GnRH antagonists

A) High intercycle endogenous FSH concentrations inducing secondary follicle

recruitment and leading to an asynchronous follicular development.

B) LH levels remain unsuppressed during the early follicular phase and enhance

E2 production.

c)High exposure of the genital tract to LH, E2 and progesterone levels during

the early follicular phase, might adversely affect the implantation rate

mainly by altering endometrial receptivity, leading to a worse reproductive

outcome.

Asynchronous follicular development

Advantages of GnRH agonist

A) Stable and low LH and P levels throughout the stimulation phase.

B)Suppression of endogenous FSH levels leading to a follicular cohort of all

small follilcles at the initiation of FSH stimulation resulting in a

synchronized follicular development.

Disadvantages of GnRH agonist

A. More time consuming and complex stimulation protocols.

B. Acute stimulation of gonadotropins and steroid hormones due to the flare

up effects ( more cyst formation).

C. Profound hypoestrogenemia due to downregulation ( hot flushes ).

D. More risk of OHSS.

GnRH antagonist protocols

A) Single dose protocol

GnRH antagonist ( 3 mg) is started on day 7 of ovarian stimulation .

B) Multiple dose protocols

• Fixed regimen: GnRH antagonist (0.25 mg )/daily from the 6th day of ovarian

stimulation .

• Flexible regimen : GnRH antagonist (0.25 mg) / daily when the follicles

reach a size of > 14 mm .

Single dose Vs. Multiple dose regimens

• No significant difference in pregnancy rates or in the inhibition of LH surge .

• Single-dose GnRH-ant protocol has the advantage of reducing the number

of injections.

• In 10 % of cases using the single dose regimen , additional daily dose of

antagonist is needed.

• In some cases 3 mg-dose may result in excessive and potentially harmful

suppression of endogenous LH.

Fixed Vs. Flexible regimens • Reduced number of antagonist injections and the duration of stimulation is

observed with the flexible regimen .

• Four RCTs have so far been performed comparing a fixed versus a flexible

protocol. Although currently the difference is not significant, all published

studies show a lower pregnancy rate in the flexible as compared to the fixed

protocol (odds ratio 0.70, 95% CI: 0.47– 1.05).

Al-Inany H, Aboulghar MA, Mansour RT, Serour GI: Optimizing GnRH antagonist administration: meta-analysis of fixed versus flexible protocol. Reprod Biomed Online 2005, 10(5):567–570.

Modifications of the standard GnRH antagonist protocol

Oral contraceptive pills pre-treatment

•It was suggested that oral contraceptive pills (OCP) pre-treatment may improve

synchronization of the recruitable cohort of ovarian follicles.

•A large meta-analysis showed no significant effect of OCP pre-treatment on

the probability of pregnancy in GnRH-ant cycles

•An increase of gonadotropin requirement, and a longer duration of treatment

was observed with the use of OCP.

Kolibianakis EM, Collins J, Tarlatzis BC, Devroey P, Diedrich K, Griesinger G: Among patients treated for IVF with gonadotrophins and GnRH analogues, is the probability of

live birth dependent on the type of analogue used? A systematic review and meta-analysis. Hum Reprod Update 2006, 12(6):651–671

GnRH agonist versus HCG for triggering final oocyte maturation

•Replacing HCG with GnRH agonist has been claimed to lead to a decreased

risk of developing OHSS in high risk patients .

• However, GnRH agonist administration induces an LH surge which is not

identical to that occurring in the natural cycle, especially regarding its duration.

•The existing literature suggests that a lower probability of pregnancy is to be

expected when a single dose of GnRH agonist is used instead of HCG for

triggering final oocyte maturation .

Griesinger G, Diedrich K, Devroey P and Kolibianakis EM (2005b) GnRH agonist for triggering final oocyte maturation in the GnRH antagonist ovarian hyperstimulation protocol: a systematic review and meta-analysis. Hum Reprod Update 12,159–168.

GnRH-ant (antagonist) protocols Vs GnRH-a (agonist) long protocol

• Significantly less gonadotropin ampoule consumption and stimulation days

in GnRH-ant regimes.

• First two met-analyses revealed that the pregnancy rates tended to be

lower in GnRH-ant regimen .

• Subsequent larger meta-analyses revealed that there are no significant

differences in the pregnancy rates and the live birth rate between both

regimens .

• Lower mean number of cumulus-oocyte-complexes (COC) and 2

pronuclear (PN) oocytes were found in GnRH-ant group.

• LH and E2 concentrations, in early follicular phase were higher in GnRH-

ant regime as compared with GnRH-a regime, whereas the LH

concentrations on the day of hCG were comparable in both protocols .

• A premature LH rise was observed in 4.3% of GnRH-ant patients and in

3% of GnRH-a patients .

• OHSS was significantly higher in GnRH-a group (1.1% P = 0.03) .

Ongoing pregnancy rate is significantly lower in the antagonist group.( P =0.03 , OR 0.82 , 95% CI 0.68 to 0.97 )

Two folds decrease in the risk of OHSS with antagonist protocols

Citation Year Effect Lower Upper PValue

Albano 2000 ,829 ,444 1,547 ,556

European 2000 ,748 ,519 1,078 ,119

Olivennes 2000 ,799 ,336 1,901 ,612

North American 2001 ,777 ,470 1,284 ,324

Middle East 2001 ,973 ,604 1,568 ,910

Akman 2001 ,760 ,177 3,263 ,712

Hohmann 2003 ,929 ,398 2,169 ,865

Martinez 2003 1,569 ,307 8,011 ,587

Franco 2003 ,545 ,065 4,562 ,573

Hwang 2004 1,105 ,347 3,526 ,866

Sauer 2004 1,067 ,334 3,409 ,913

Xavier 2005 ,845 ,288 2,484 ,760

Loutradis 2005 ,704 ,271 1,827 ,469

Malmusi 2005 1,000 ,257 3,888 1,000

Marci 2005 10,358 ,533201,451 ,062

Cheung 2005 1,550 ,242 9,940 ,642

Check 2005 1,818 ,518 6,382 ,347

Barmat 2005 ,651 ,262 1,621 ,356

Bahceci 2005 ,839 ,436 1,613 ,598

Badrawi 2005 ,803 ,320 2,015 ,640

Schmidt 2005 1,000 ,181 5,533 1,000

Lee 2005 ,696 ,229 2,114 ,522

FixedCombined (22) ,859 ,722 1,021 ,085

0,1 0,2 0,5 1 2 5 10

Favor agonists Favor antagonists

Odds ratio:0.859p=0.085

LIVE BIRTH

Rate difference2.7%

3.0 ampoules less with GnRH antagonistsp<0.07

FSH requirement

COCs retrieved

1.2 COCs more with GnRH agonists

p<0.001

Review: GnRH Antagonists vs. GnRH agonistsComparison: 02 COCs Outcome: 01 COCs retrieved

Study Antagonists Agonists WMD (random) Weight WMD (random)or sub-category N Mean (SD) N Mean (SD) 95% CI % 95% CI Year

Albano 166 8.00(4.90) 72 10.60(6.60) 5.97 -2.60 [-4.30, -0.90] 2000Olivennes 113 9.20(5.10) 36 12.60(7.40) 3.79 -3.40 [-5.99, -0.81] 2000Akman 20 4.50(1.63) 20 5.50(2.98) 6.63 -1.00 [-2.49, 0.49] 2001European 463 8.70(5.60) 238 9.70(6.20) 8.53 -1.00 [-1.94, -0.06] 2001Middle East 226 7.90(5.10) 111 9.60(6.80) 6.83 -1.70 [-3.13, -0.27] 2001Franco 14 10.50(6.50) 6 10.10(4.60) 1.38 0.40 [-4.61, 5.41] 2003Martinez 23 3.70(1.90) 21 5.60(4.30) 5.13 -1.90 [-3.90, 0.10] 2003Hwang 25 16.30(6.40) 27 17.60(5.90) 2.65 -1.30 [-4.65, 2.05] 2004Badrawi 47 9.68(5.28) 50 12.60(6.15) 4.44 -2.92 [-5.20, -0.64] 2005Bahceci 59 19.33(9.00) 70 21.60(11.00) 2.54 -2.27 [-5.72, 1.18] 2005Barmat 36 12.50(3.28) 41 15.00(4.50) 5.83 -2.50 [-4.25, -0.75] 2005Check 24 9.60(7.70) 30 17.60(10.10) 1.51 -8.00 [-12.75, -3.25] 2005Cheung 19 5.89(3.02) 21 5.62(4.17) 4.52 0.27 [-1.97, 2.51] 2005Loutradis 58 8.10(2.40) 58 8.70(3.00) 8.35 -0.60 [-1.59, 0.39] 2005Malmusi 18 2.50(1.20) 24 3.50(1.40) 9.03 -1.00 [-1.79, -0.21] 2005Marci 29 5.60(1.60) 26 4.30(2.20) 8.22 1.30 [0.27, 2.33] 2005Schmidt 14 8.90(0.90) 12 9.00(1.20) 8.90 -0.10 [-0.93, 0.73] 2005Xavier 53 10.10(4.60) 59 10.60(5.00) 5.73 -0.50 [-2.28, 1.28] 2005

Total (95% CI) 1407 922 100.00 -1.19 [-1.82, -0.56]Test for heterogeneity: Chi² = 48.11, df = 17 (P < 0.0001), I² = 64.7%Test for overall effect: Z = 3.70 (P = 0.0002)

-10 -5 0 5 10

Favor agonists Favor antagonists

Citation Year Rate1 Rate2 PValue Effect Lower Upper

Albano 2000 ,00 ,01 ,20 ,16 ,01 3,91

Badrawi 2005 ,04 ,04 1,00 1,00 ,15 6,82

Bahceci 2005 ,04 ,07 ,49 ,62 ,15 2,49

European 2000 ,01 ,02 ,07 ,33 ,10 1,17

Lee 2005 ,07 ,10 ,72 ,73 ,13 4,04

Middle East 2001 ,02 ,05 ,07 ,34 ,10 1,17

North American 2001 ,01 ,02 ,76 ,76 ,13 4,46

Olivennes 2000 ,02 ,05 ,25 ,34 ,05 2,35

RandomCombined (8) ,01 ,47 ,27 ,84

0,01 0,1 1 10 100

Favor agonists Favor antagonists

RR : 0.47~ 2 times less risk to be admitted due to OHSS with GnRH antagonists

Hospital admission due to OHSS

In conclusion

• The GnRH antagonist protocol is a short and simple protocol with a

comparable live-birth rate to GnRH agonists long protocol .

Furthermore , it is associated with less incidence of the OHSS.