Association of number of retrieved oocytes with live birth rate and birth weight: An analysis of 231,815 cycles of in vitro fertilization

Objective: To determine if number of retrieved oocytes correlates with live birth rate and incidence of low birth weight (LBW). Design: Retrospective cohort. Setting: Not applicable. Patient(s): Women undergoing fresh embryo transfer with the use of either autologous (n = 194,627) or donor (n = 37,188) oocytes whose cycles were reported to the Society for Assisted Reproductive Technology in the years 2004-2010. Intervention(s): None. Main Outcome Measure(s): Live birth rate, birth weight, birth weight z-score, LBW. Result(s): For both autologous and donor oocyte cycles, increasing number of retrieved oocytes paralleled live birth rate and embryos available for cryopreservation in most analyses, with all models adjusted for age and previous births. For cycles achieving singleton pregnancy with the use of autologous oocytes via transfer of two embryos, a higher number of retrieved oocytes was associated with lower mean birth weight, lower birth weight z-score, and greater incidence of LBW. In contrast, for cycles using donor oocytes, there was no association of number of retrieved oocytes with measures of birth weight. Conclusion(s): A higher number of retrieved oocytes was associated with an increased incidence of LBW in autologous singleton pregnancies resulting from transfer of two embryos, but not in donor oocyte cycles. Although the effect of high oocyte number on the incidence of LBW in autologous cycles was of modest magnitude, further study is warranted to determine if a subgroup of women may be particularly vulnerable.