Does Blastocyst Transfer Affect Sex Ratio?

Abstract

Objective: Advances in embryo culture have made blastocyst transfer (BT) a valuable technique in IVF. Embryos with the fastest cleavage rates and the best morphologic appearance are selected for transfer. Evidence exists that male embryos may grow more rapidly than female embryos. Recent published data (Menezo, et. al. Fertil Steril 1999; 72:221) have noted that there is a significant increase in the ratio of male offspring (58%) with fresh blastocysts grown in co-culture. Thus, concern exists regarding whether BT might result in an altered sex ratio favoring males. The objective of this study was to assess the sex ratio of pregnancies resulting from fresh BT in sequential media. Design: Retrospective chart review of pregnancies resulting from fresh BT at two academic institutions. Materials and Methods: Sequential embryo culture was performed using either P1 +10%SSS/Blastocyst medium + 10%SSS (Irvine Scientific) or IVF500/S2 (Scandinavian Science) or G1/G2 (Scandinavian Science.) Based on degree of embryo expansion and the presence of a distinct inner cell mass and trophectoderm the best 2 or 3 blastocysts were chosen for transfer on day 5. Results: 150 pregnancies resulted in 200 offspring with 112 (56%) males and 88 (44%) females. The difference did not reach statistical significance (p>0.05.) Conclusion: Even if a 56/44 male to female ratio such as ours were to be confirmed by a larger series, this is not so drastically different than the ratio of 107/100 (i.e. 51.7%/48.3%) reported in the general population. We believe that this slight trend for male offspring should not deter IVF programs from adopting BT with all of the advantages it offers at optimizing pregnancy rates while minimizing high-order multiple gestation.