According to research conducted at the Mount Sinai School of Medicine and Reproductive Medicine Associates in New York City, boys are more likely to result from blastocyst transfer after in vitro fertilization (IVF). The study found that nearly 58 percent of babies born via blastocyst transfer after a fresh IVF cycle were male. In the U.S. approximately 51 percent of babies are male.
The study, published in the June 2007 on-line edition of Fertility & Sterility, analyzed 1,284 infants from 937 deliveries that occurred from August 2003 to August 2005 as a result of fresh IVF cycles. The researchers also looked at the sex ratios for deliveries resulting from embryos transferred on the third day of culture, as well as blastocysts transferred after five days of culture.
Moreover, the study took into account how the practice of single blastocyst transfer might impact the sex ratio. Results from embryos transferred on day three of culture exhibited a much more balanced sex-ratio, 48.8 percent female to 51.2 percent male, which is close to that of all US births. There was no significant change in sex ratio for singleton deliveries from day three transfers. However, when the data from singleton births after blastocyst transfer were studied, a sex ratio of 36.3 percent female to 63.7 percent male appeared.
The researchers believe that the higher male ratio is attributed to the faster preimplantation development of male embryos. Since embryologists choose the most fully developed embryos for transfer, males usually result.