Blastocyst transfer does not cause a sex-ratio imbalance

Objective: To determine whether either single or double fresh blastocyst transfers result in a sex-ratio imbalance in resulting offspring compared with transfers on day 2 or 3 and whether there is a correlation between rate of embryo development and sex of the embryo. Design: Retrospective analysis. Setting: Large IVF center. Patient(s): Four hundred thirty-five live births from single fresh ETs for the period January 2005 through July 2007 and 2,043 live births from double ETs for the same period. Intervention(s): Statistical analysis performed on sex ratio of offspring resulting from transfers (day 2, day 3, day 4, and blastocyst), as well as on the stage of development reached for each day in culture analyzed on sex of the embryo. Main Outcome Measure(s): Sex ratio of offspring by day of transfer. Stage of embryonic development by sex for each day in culture. Result(s): There was no difference in sex ratio with blastocyst transfer (single or double). There was no difference in speed of embryonic development at any stage in vitro. Conclusion(s): Male embryos do not grow faster than female embryos in culture. Blastocyst transfer does not result in a sex-ratio imbalance in resulting offspring. (Fertil Steril (R) 2009;92:1302-5. (C) 2009 by American Society for Reproductive Medicine.)