According to a new study, frozen eggs used in vitro fertilization produce less successful births than fresh eggs, although the difference is marginal. Researchers at the Center for Human Reproduction in New York culled data from 380 fertility clinics in the United States, where 92 percent of all IVF births take place. The research dates back to 2013, when the American Society for Reproductive Medicine declared that oocyte cryopreservation, or freezing donated eggs, was no longer limited to experimental procedure.

Women who implanted their embryos with fresh eggs generated live births 49.6 percent of the time while women who used frozen eggs produced births 43.2 percent of the time. However, when the number of embryos was factored into the study, the live birth rate jumped to 56.1 percent for fresh eggs and 47.1 percent for frozen eggs.

However, there was also a small margin in how many embryos were transferred. Women using frozen eggs transferred an average of 1.6 embryos per IVF cycle compared to women who were using fresh eggs had transferred 1.7 embryos.

The data only measured donor eggs, not women who froze their own for future IVF. Select donors are screened for health qualifications, so pregnancy rates will differ with women who are older.

The scientists who conducted the study published by the Journal of the American Medical Association wrote,”The reasons for lower live birth rates with use of cryopreserved oocytes remain to be established.” Researchers also added, “One possible explanation is less opportunity for proper embryo selection due to smaller tarting numbers of oocytes, leading to fewer embryos available for transfer. Alternatively, oocyte quality may be negatively affected by cryopreservation and thawing.”

Source: UPI