Pregnancy-related complications and perinatal outcomes resulting from transfer of cryopreserved versus fresh embryos in vitro fertilization: a meta-analysis

This meta-analysis suggests that pregnancies generated with the use of frozen-thawed embryo transfer have lower risks of adverse birth outcomes but are associated with higher risks of pregnancy-induced hypertension and large for gestational age.

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Volume 109, Issue 2, Pages 330–342.e9


Tingting Sha, M.D., Xunqiang Yin, M.D., Wenwei Cheng, M.D., Isaac Yaw Massey, M.D.



To provide an updated comparison of pregnancy-related complications and adverse perinatal outcomes of pregnancies conceived after frozen embryo transfer (FET) versus fresh embryo transfer (fresh ET).






Pregnancies resulting from FET versus fresh ET.


Pubmed, Embase, Cochrane Library, Google Scholar, and Chinese databases, including the China National Knowledge Infrastructure Database, Wanfang, and Chinese Scientific Journals Full-Text Database were searched by two independent reviewers from January 1980 to September 2017. The results were expressed as risk ratios with 95% confidence intervals.

Main Outcome Measure(s)

Pregnancy-related complications and perinatal outcomes.


Our search retrieved 1,397 articles, of which 31 studies were included. Pregnancies resulting from FET were associated with lower relative risks of placenta previa, placental abruption, low birth weight, very low birth weight, very preterm birth, small for gestational age, and perinatal mortality compared with fresh ET. Pregnancies occurring from FET were associated with increased risks of pregnancy-induced hypertension, postpartum hemorrhage, and large for gestational age compared with fresh ET. The risks of gestational diabetes mellitus, preterm premature rupture of the membranes, and preterm birth (PTB) showed no differences between the two groups.


Our analysis demonstrated that FET results in lower risks of placenta previa, placental abruption, low birth weight, very low birth weight, very preterm birth, small for gestational age, and perinatal mortality than fresh ET, some differences that are attributed to the increased risks of pregnancy-induced hypertension, large for gestational age, and postpartum hemorrhage. Although cryotechnology keeps improving, for comprehensive consideration, individual approaches remain appropriate to balance the options of FET or fresh ET at present.

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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. The journal publishes juried original scientific articles in clinical and laboratory research relevant to reproductive endocrinology, urology, andrology, physiology, immunology, genetics, contraception, and menopause. Fertility and Sterility® encourages and supports meaningful basic and clinical research, and facilitates and promotes excellence in professional education, in the field of reproductive medicine.