Merviel P, Bouee S, Jacamon AS, et al. - The objectives of this retrospective study were to determine whether blastocyst transfer gave higher pregnancy rates than cleaved embryo transfer at day 3 in both the general and selected in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) populations and if the serum progesterone level influenced the pregnancy rate. Researchers evaluated IVF/ICSI cycles with Gonadotropin-releasing hormone antagonist - follicle-stimulating hormone/human menopausal gonadotropin protocols in a general population (n = 1,210) and a selected “top cycle” population (n = 677), after blastocyst transfer on day 5 or cleaved embryo transfer on day 3. Predictive factors for pregnancy were recorded and the progesterone to oocyte index, the progesterone: estradiol ratio (P: E2 ratio), and the progesterone to follicle (> 14 mm) index were calculated. The data demonstrate that blastocyst transfers were correlated with higher clinical pregnancy and birth rates than cleaved embryo transfers in a general population but not in a selected population. It was shown that serum progesterone levels on the eve of the trigger day and on the day itself predicted the likelihood of pregnancy.