**7. Human chorionic gonadotropins (hCG)**

The use of hCG is driven by the hypothesis that, in addition to progesterone and estrogen, the corpus luteum produces other hormones which are required for endometrial transformation and optimization of the conditions for embryo implantation and development. Some randomized trials supported the use of hCG for luteal support [58 ,59].However one randomized controlled trial [60] where patients at ovum pick –up were randomized to receive luteal support as either progesterone only or hCG only or combination of progesterone and hCG showed that there were no statistically significant differences with regard to the main outcome parameter, the clinical ongoing pregnancy rate .However using a standardized discomfort scale, there were more complaints towards the end of the luteal phase in the groups receiving hCG only or an additional injection of hCG, when compared to the progesterone only groups .The conclusion of the study was that progesterone only for luteal phase support leads to the same clinical ongoing pregnancy rate as hCG, but has no impact on the comfort of the patient. Furthermore two meta-analyses [18 ,19] found no statistically signicant differences in clinical pregnancy, ongoing pregnancy, and miscarriage rates between progesterone and hCG. The odds ratio of OHSS was more than threefold higher when hCG was added to the luteal phase support regimen, conrming that progesterone alone is a better strategy. In the most recent Cochrane review and meta-analysis [21], 15 studies, including 2117 women investigated progesterone versus hCG regimens. The hCG regimens were sub grouped into comparisons of progesterone versus hCG and progesterone versus progesterone + hCG. The results did not indicate a difference of effect between the interventions, except for OHSS. Furthermore subgroup analysis of progesterone versus progesterone + hCG showed a significant benefit from progesterone (Peto OR 0.45, 95% CI 0.26 to 0.79).
