Fresh, frozen embryos offer very similar birth rates

Researchers have found that there is an insignificant difference in live birth rates between in vitro fertilization methods using frozen or fresh embryos.

Many women struggling to have a baby turn to in vitro fertilization to improve their chances, but then face further uncertainty and anxiety when confronted with the decision of whether to use frozen or fresh embryos.

Researchers monitored 2,157 women who were undergoing their first in vitro fertilization cycle and were randomly assigned either fresh or frozen embryos.

Researchers found that women using frozen embryos had a live birth rate of 48.7 percent as compared to a live birth rate of 50.2 percent for women in the fresh-embryo group. There were also no significant differences between the groups in rates of implantation, clinical pregnancy, overall pregnancy loss, and ongoing pregnancy.

The study, however, did find that frozen-embryo transfers resulted in a significantly lower risk of ovarian hyperstimulation syndrome (OHSS) than women using fresh-embryo transfers.

While most cases of the syndrome are minor, severe cases can lead to illness and even death. Women using frozen embryos were found to have a 0.6 percent chance of developing OHSS, versus a 2 percent chance for women receiving fresh embryos.

“This is an emerging issue of immediate and important concern for couples who are seeking in vitro fertilization treatment,” says Heping Zhang, professor of biostatistics at the Yale University School of Public Health.

Reports by the Society for Assisted Reproductive Technology have noted that more fertility centers choose to defer embryo transfer by freezing embryos, Zhang says. The researchers’ say they believe this is the first time that a large clinical trial has been conducted to evaluate this change of practice.

Zhang says that the findings will have an immediate effect on patients and clinicians in their evaluation and consideration with regard to the risk and benefit of different embryo transfer strategies.

The National Key Research and Development Program of China and the National Natural Science Foundation of China funded the work, which appears in the New England Journal of Medicine.

Source: Yale University

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