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Member Research & Reports

Member Research & Reports

Yale Study Finds Frozen Embryos May Improve IVF Outcomes for Some Women

Frozen embryos may be better and safer than fresh embryos for women with polycystic ovary syndrome (PCOS) who use in vitro fertilization to conceive children, new research by an international consortium has found.

Baby feet in the playpen. Close up.

The collaboration between the Yale School of Public Health, 13 universities in China and Penn State College of Medicine showed that frozen embryos may improve the rate of live births and lower the rates ovarian hyperstimulation syndrome and pregnancy complications in women with PCOS. The scientists believe this is because frozen embryo transfer allows a woman’s ovary to recover from potentially harmful ovarian stimulation during in vitro fertilization and also allows time for her exposed endometrial lining to shed.

“This is a scientifically and clinically important finding in reproductive health,” said Dr. Heping Zhang, the Susan Dwight Bliss Professor of Public Health (Biostatistics), professor in the Child Study Center, director of the Collaborative Center for Statistics in Science (C2S2) at the School of Public Health and one of the study’s lead authors. “It also set up a model of international collaboration in clinical trials in China.”

Other leaders of the consortium include Zijiang Chen at Shangdong University in China and Richard Legro of Penn State College of Medicine. The findings are published in the New England Journal of Medicine.

The scientists randomly assigned 1,508 infertile women with polycystic ovary syndrome in China who were undergoing their first IVF cycle to undergo either fresh-embryo transfer or embryo cryopreservation followed by frozen-embryo transfer.  After three days of embryo development, the women underwent the transfer of up to two fresh or frozen embryos.

The frozen-embryo transfer resulted in a higher frequency of live births after the first transfer than did fresh-embryo transfer (49.3 percent versus 42 percent).  Women who underwent frozen-embryo transfer also had fewer incidences of pregnancy loss (22.0 percent versus 32.7 percent) and of ovarian hyperstimulation syndrome (1.3 percent versus 7.1 percent).

However, a higher frequency of preeclampsia (4.4 percent versus 1.4 percent), a serious condition of pregnancy characterized by high blood pressure, was observed in women who underwent frozen-embryo transfer. There were also five neonatal deaths in the frozen-embryo group and none in the fresh-embryo group. None of the patients in the study developed severe preeclampsia pressure during pregnancy and the difference in neonatal death rates was not statically significant.

In vitro fertilization has been used in the births of more than five million infants worldwide, but there are some concerns about the procedure’s safety. IVF pregnancies are associated with greater maternal and neonatal complications, including preeclampsia, preterm delivery, low birth weight and congenital anomalies, than are spontaneous pregnancies. Women with polycystic ovary syndrome who undergo IVF are at increased risk for ovarian hyperstimulation syndrome (OHSS,), which can occur after injectable hormone medications are used during IVF. Severe OHSS can cause rapid weight gain and abdominal pain, among other symptoms.

The mechanisms and cost implications of the findings need further study, as well as whether a similar benefit persists in couples with unexplained infertility, the researchers said.