The influence of supernumerary embryos on the clinical outcome of IVF cycles.

Purpose: To assess the influence of the presence of quality supernumerary embryos on the clinical outcome and risk of multiple conception in patients having their first in vitro fertilization (IVF) cycle.

Methods: Retrospective cohort study of 1448 women having their first IVF treatment cycle who received 4004 embryos where at least six embryos were available for transfer treated in an Assisted Conception Unit based in a large teaching hospital.

Results: The replacement of three rather than two embryos to women under 35 years who had good-quality supernumerary embryos resulted in a higher twin (12.5 vs. 11.9%) and triplet birth rates (2.1 vs. 0%), without significantly improving the clinical pregnancy (50.5 vs. 45.2%) or total live birth rates (38.9 vs. 35.7%). In the absence of quality spare embryos, these women who had three rather than two embryos replaced had a significantly higher clinical pregnancy rate (39.3 vs. 28.8%; P = 0.04), total live birth (32.7 vs. 19.4%; P = 0.02) and singleton birth rate per cycle (20.8 vs. 14.4%; P = 0.04), without significantly influencing the multiple birth rate. In women over 35 years, the replacement of three instead of two embryos in the presence or absence of quality supernumerary embryos led to a significant improvement in clinical outcome, without being associated with a concurrent increase in the multiple birth rate. Women in both age groups who had either two or three embryos replaced in the presence of quality supernumerary embryos had a notably better clinical outcome compared with their counterparts who had the same number of embryos replaced, but with no quality embryos to spare.

Conclusions: The presence of good-quality supernumerary embryos can be used as a reference to determine the optimal number of embryos to transfer and as an indicator of the probability of success of an individual couple in a given cycle. Optimal pregnancy rates and simultaneous reduction of multiple gestation can be achieved with a flexible embryo replacement policy that is based on embryo quality, maternal age, and the presence or absence of surplus quality embryos.