Objective: To compare the sex ratio of offspring born after cleavage stage embryo transfer and blastocyst transfer.
Materials and methods: In this retrospective study of embryo transfer (ET), we included 473 offspring from 446 deliveries during the period January 2002 to December 2007. Statistical analysis was performed on the sex ratio of offspring resulting from day 3 cleavage stage embryo transfer and from sequential blastocyst culture transfer.
Results: In total, 446 patient deliveries were included in this analysis. There were 251 singleton pregnancies, 109 twin pregnancies, and four triplet pregnancies. The total number of offspring was 473, of which 118 resulted from day 3 ETs, and 355 resulted from blastocyst ETs. At our center, the influence on the sex ratio of cleavage stage ET and blastocyst-stage ET showed a bias towards males in both cases. The overall female to male ratio for offspring resulting from day 3 ETs was not significantly higher than the same ratio for offspring resulting from blastocyst ETs (p = 0.24; odds ratio, 0.762). The female to male ratio for either singleton births or multiple deliveries was also not significantly different between day 3 ETs and blastocyst ETs.
Conclusion: The sex ratio was influenced by cleavage stage ET and blastocyst-stage ET. In both cases, there was a bias towards males. In addition, when blastocyst ET was compared with day 3 ET, there was no further increase in the percentage of male offspring.