The purpose of this study is to compare two luteal support protocols in In vitro fertilization patients (IVF) and are at risk of developing ovarian hyperstimulation syndrome (OHSS). We would like to determine whether luteal Decapeptyl on days 3, 6,9 post ovulation triggering is as good as low dose hCG on day 3 post triggering..

This is randomized clinical trial studying two luteal support protocols of In vitro fertilization patients (IVF) treated by a GnRH antagonist (GnRH ant) protocol and are at risk of developing ovarian hyperstimulation syndrome (OHSS). The randomization procedure will be performed by a third party in the hospital by using a randomization table: patients fulfilling the inclusion and exclusion criteria and giving their informed consent will be randomized into one of two arms. This study does not include any intervention affecting the ovarian stimulation and is solely intended to test the post ova pickup period.

One arm will be treated by luteal Decapeptyl on days 3, 6,9 post ovulation triggering. Second arm will be treated by low dose hCG on day 3 post triggering. All patients to be recruited are treated for acceptable IVF indications in Meir medical center (MMC) and their registry is computerized in the general system of MMC. For the purpose of the study we will use the only the data of patients recruited to the study and were giving their informed consent. Each patient recruited will have a unique study identity (ID) . The patients' information will be pooled from the computerized file into an Excel spread sheet: in this Excel file the names will be erased and only the unique study ID will appear. The information regarding the coding key will be kept as a hard copy in a locked room inside the IVF unit in a special study folder. The study was approved by MMC institutional Helsinki board.

The data retrieved for each patients is not unique for the study but includes the basic variables monitored in every IVF cycle : Estradiol serum levels (E2), Progesterone serum levels (P), number of follicles as counted by trans-vaginal ultrasound, endometrial thickness as measured by trans-vaginal ultrasound, Follicle stimulating hormone (FSH) dosing, number of stimulation days, number of eggs retrieved, fertilization rate, blastulation rate, number of embryos transferred, embryo quality, positive pregnancy test, implantation rate, presence of a clinical pregnancy, presence of OHSS. Since these are mandatory variables in the treatment we do not expect any missing data. In addition to these mandatory data the study patients will be performing two additional blood tests on day 3 post ovum pickup and on the transfer day itself (day 5 post ovum pickup) including Estradiol serum levels (E2) and Progesterone serum levels (P).

Outcome measures: Day of transfer Progesterone serum levels, OHSS rate, implantation rate, clinical pregnancy rate.

Sample size calculation based on Kol S et al 2015, regarding the day of transfer Progesterone level (pooled standard deviation: 40nmol/L), alpha of 5%, 80% power, then a non-inferiority study will require 22 patients in each group and a total of 44 patients. Once including an expected 10% chance of freeze all in this population we will include 50 patients.

Statistical analysis: Analysis of data was performed using the SPSS 23.0 computer package (SPSS Inc., Chicago, IL). Normally distributed data were analyzed by student t test . χ2 or Fisher's exact test will be used for comparisons of rates and proportions. All P values were tested as two-sided and considered significant at less than 0.05.

Inclusion Criteria:

• IVF treatment
• GnRH antagonist protocol
• GnRH agonist triggering of ovulation
• High risk for OHSS as expressed by either E2 serum level >2500 pg/ml

Exclusion Criteria:

• background maternal morbidity
• Any protocol other than GnRH antagonist protocol
• hCG triggering of ovulation
• E2 serum level >4500 pg/ml
• Aspiration of >25 ova
• Embryo transfer prior to day 5