Obstetric complications after frozen versus fresh embryo transfer in women with polycystic ovary syndrome: results from a randomized trial

Frozen embryo transfer results in higher risks of large for gestational age in singleton pregnancy and pre- eclampsia in twin pregnancy than fresh embryo transfer in women with polycystic ovary syndrome.

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Volume 109, Issue 2, Pages 324–329


Bo Zhang, M.D., Ph.D., Daimin Wei, M.D., Ph.D., Richard S. Legro, M.D., Yuhua Shi, M.D., Ph.D., Jing Li, M.S., Lin Zhang, M.S., Yan Hong, M.D., Ph.D., Gang Sun, Ph.D., Ting Zhang, M.D., Ph.D., Weiping Li, M.D., Ph.D., Zi-Jiang Chen, M.D., Ph.D.



To evaluate the effect of frozen embryo transfer on maternal and neonatal complications of singleton and twin pregnancies compared with fresh embryo transfer in women with polycystic ovary syndrome (PCOS).


A secondary analysis of a multicenter, randomized, controlled trial comparing live birth after frozen vs. fresh embryo transfer (FreFro-PCOS).


Reproductive medicine centers.


A total of 1,508 patients with a diagnosis of PCOS who were undergoing IVF were enrolled.


On day of oocyte retrieval, eligible patients were randomized to the fresh or frozen embryo transfer groups. Up to two embryos were transferred in both groups. All pregnancies were followed up until delivery.

Main Outcome Measure(s)

Gestational diabetes mellitus, pre-eclampsia, preterm birth, small for gestational age, and large for gestational age.


The risks of gestational diabetes mellitus, preterm birth, and small for gestational age were comparable between the frozen and fresh embryo transfer groups in both singleton and twin births. However, singleton infants born after frozen embryo transfer were more likely to be large for gestational age (25.2% vs. 17.5%; relative risk 1.44, 95% confidence interval 1.01–2.07, P=.044) than those born after fresh embryo transfer. Twin pregnancy after frozen embryo transfer had a higher risk of pre-eclampsia (12.0% vs. 2.8%; relative risk 4.31, 95% confidence interval 1.27–14.58, P=.009) than those after fresh embryo transfer.


In women with PCOS, frozen embryo transfer resulted in an increased risk of large for gestational age in singleton pregnancy and a higher risk of pre-eclampsia in twin pregnancy.

Clinical Trial Registration Number


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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility® is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders.