Short coincubation of gametes in in vitro fertilization improves implantation and pregnancy rates: a prospective, randomized, controlled study

OBJECTIVE: To examine the benefits of short coincubation of gametes compared to prolonged incubation in in vitro fertilization (IVF). DESIGN: Prospective randomized controlled study. SETTING: Hospital-based fertility center. PATIENT(S): One hundred thirty patients (group 1) and 129 patients (group 2). INTERVENTION(S): Oocytes from group 1 were exposed to spermatozoa for 2 hours, and oocytes from group 2 were exposed to spermatozoa for 20 hours. MAIN OUTCOME MEASURE(S): Fertilization and cleavage rates, embryo quality, and pregnancy and implantation rates were evaluated. Estradiol (E(2)) and progesterone (P(4)) levels were measured in the wells of culture dishes after 2-hour exposure of oocytes/zygotes to spermatozoa in group 1 and after 20-hour exposure in both the groups. RESULT(S): There was no difference between the two groups in the fertilization rate and the number of embryos obtained. However, the proportion of grade 1 embryos was significantly higher among group 1 compared to group 2 patients. Clinical pregnancy and implantation rates were significantly higher among group 1 compared to group 2. The significantly higher levels of E(2) and P(4) in the 20-hour cultures compared with the 2-hour cultures may have been detrimental to embryo quality, pregnancy, and implantation rates. CONCLUSION(S): Coincubation of gametes for 2 hours with standard or high insemination concentrations of spermatozoa significantly improved embryo quality and the pregnancy and implantation rates compared with overnight incubation of gametes.