Intracytoplasmic sperm injection of a human oocyteWIKIMEDIA, EUGENE ERMOLOVICHOffspring conceived by in vitro fertilization (IVF) are more likely to be male than female. Now, a team led by Jianhui Tian of China Agricultural University in Beijing has found that problems with X chromosome inactivation, the process of silencing one of the female embryo’s X chromosomes, is responsible for much of this sex-ratio skew in mice. The team also demonstrated a method of reversing the male-dominant ratio by modifying the culture that murine preimplantation IVF embryos are grown in. The team’s results were published in PNAS today (March 7).
Paulo Rinaudo, a reproductive endocrinologist with the University of California, San Francisco, who was not involved in the study, noted that researchers previously suspected X chromosome inactivation played some role in this phenomenon. “The authors did a great job in going after a mechanism,” Rinaoudo wrote in an email.
In the U.S., around 1.5 percent of newborns are conceived via IVF. Elsewhere, the rate of IVF-conceived babies is as high as 4 percent. The assisted reproductive technology is also extensively used in cow, pig, and other livestock breeding programs, where researchers began documenting the skew toward male offspring in the early 1990s. In the past decade, a similar sex ratio has been found among human IVF embryos, but supporting evidence for the imbalance was inconsistent.
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