Implications of Assisted Reproductive Technologies on Term Singleton Birth weight An Analysis of 25777 Children in the National Assisted Reproduction Registry of Japan

An analysis of 25,777 singleton full-term births after assisted reproduction showed that extended embryo culturing and frozen-thawed embryo transfer increased birth weight and that ovarian stimulation is a risk factor for low birth weight in fresh embryo transfer cycles.

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Akira Nakashima, M.D., Ryuichiro Araki, Ph.D., Hirohiko Tani, M.D., Osamu Ishihara, M.D., Ph.D., Akira Kuwahara, M.D., Ph.D., Minoru Irahara, M.D., Ph.D., Yasunori Yoshimura, M.D., Ph.D., Takeshi Kuramoto, M.D., Ph.D., Hidekazu Saito, M.D., Ph.D., Ari Nakaza, B.S., Tetsuro Sakumoto, M.D., Ph.D.

Volume 99, Issue 2, Pages 450-455, February 2013



To evaluate the implications of Assisted Reproductive Technology (ART) on neonatal birthweight.


A retrospective study using analysis of covariance and multiple logistic regression analysis of the Japanese ART registry.


Japanese institutions providing ART treatment.


A total of 25,777 singleton neonates reaching term gestation following ART during a period ranging from 2007-2008, with 11,374 achieved through fresh embryo transfers (fresh ET) and 14,403 achieved through frozen thawed embryo transfers (FET).



Main outcome measure(s):

Birth weight.


The mean birthweight after FET was significantly higher when compared to fresh ET and all Japanese births (3100.7 ± 387.2 g, 3009.8 ± 376.8 g, 3059.6 ± 369.6 g, respectively). The risk for low birthweight in FET was significantly lower when compared to fresh ET (OR 0.71, [95% CI, 0.63 to 0.80]). In fresh ET, ovarian stimulations were associated with about twofold risk of low birthweight when compared to natural cycle. With regards to the duration of embryonic culture, the risks resulting from a shorter culturing time were significantly higher when compared to a longer culturing time (OR1.18, [95% CI, 1.00 to 1.40]) in fresh ET.


The best method of embryo transfer for fetal growth was FET after extended culturing until blastocyst stage. However, further investigations should be performed to understand the safety of ART treatment.

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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.