The gonadotrophin preparations commonly used in assisted reproductive technology (ART) procedures contain similar folliclestimulating hormone (FSH) concentrations but differ extensively in their luteinizing hormone (LH)-activity1. MENOPUR (highly purified human menotrophin) has the highest concentration of human chorionic gonadotrophin (hCG) – a source of long acting LH-activity – of all commercially available gonadotrophin preparations. The hCG-driven LH-activity found in MENOPUR has been demonstrated to positively influence ART outcomes at the level of the embryo and endometrium. The European and Israeli Study Group (EISG) investigation and, more recently, the Menotrophin versus Recombinant FSH in vitro fertilization Trial (MERiT) established the impact of hCG-driven LH-activity in in vitro fertilization (IVF)2,3. In patients undergoing IVF, MENOPUR has shown equivalent safety profiles and a significantly higher live birth rate compared with recombinant FSH (rFSH)4,5. MERiT showed that the hCG-driven LHactivity in MENOPUR resulted in different hormone profiles compared with rFSH6. Progesterone levels at the end of stimulation Abstract of the 8th Royan International Twin Congress, Tehran, Iran, 5-7 September 2007 54 Yakhteh Medical Journal, Vol 9, Sup 1, Summer 2007 and on the day of oocyte retrieval were significantly lower in the MENOPUR patients compared with the rFSH group6. This has a probable impact on the quality of the endometrium and subsequently, embryo implantation. Additionally, it was shown that hCG levels on day 6 were highly predictive for ongoing pregnancy after IVF7. This suggests that hCG should be given from the beginning of stimulation, and possibly at higher doses, in patients who have reduced hCG levels on day 6 in order to increase the likelihood of pregnancy.