Blastocyst Transfer Skews Embryo Sex Ratio and Increases Risk of Twinning

Blastocyst transfer skews embryo sex ratio and increases twinning risk
Source: Fertility and Sterility 2008; Advance online publication
Assessing the gender ratio and risk for monozygotic twinning in IVF involving blastocyst transfer compared with transfer of cleavage-stage embryos.

MedWire News: Using blastocyst transfer rather than cleavage-stage embryo transfer during IVF significantly increases the chances of male embryos and monozygotic twinning, show findings from a systematic review and meta-analysis.

"These risks associated with blastocyst transfer should be taken into account when counseling infertility patients," suggest Byung Chul Lee and co-researchers from Seoul National University in Korea.

Lee and colleagues collated data from 13 studies involving 2,587 offspring and 40,917 IVF cycles over 12 years. Analysis of these data revealed that IVF was significantly more likely to produce a male embryo when blastocyst transfer was performed than when cleavage-stage embryo transfer was performed, at an odds ratio (OR) of 1.29.

"We found a sex ratio imbalance for pregnancies that resulted from blastocyst transfer, with 56.8 percent male infants after blastocyst transfer and 50.9 percent male infants after cleavage-stage transfer," the researchers report.

Blastocyst transfer was also associated with an approximately three-fold increase (OR = 3.04) in the risk for monozygotic twinning, compared with cleavage-stage embryo transfer.

Lee and team conclude that previous research that found no link between gender ratio and blastocyst transfer lacked statistical power.