Comparison of birth weights in patients randomly assigned to fresh or frozen-thawed embryo transfer

Birth weights were lower in patients randomly assigned to receive fresh blastocyst transfer when compared with those randomly assigned to freeze-all followed by thaw and blastocyst transfer.

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Volume 106, Issue 2, Pages 317-321


Bruce S. Shapiro, M.D., Ph.D., Said T. Daneshmand, M.D., Carrie E. Bedient, M.D., Forest C. Garner, M.Sc.



To estimate birth weight differences between patients randomized to fresh or thawed ET.


Post hoc analysis of results from two similar randomized trials.


Private fertility center.


One hundred thirty-four first-time IVF patients, ages 18–40 years at oocyte retrieval, who had live birth.


Patients were randomly assigned to have either fresh blastocyst transfer or all bipronuclear oocytes frozen followed by thaw, extended culture, and blastocyst transfer in a subsequent cycle. Preimplantation genetic screening was not allowed.

Main Outcome Measure(s)

Mean birth weight.


After allowing for the contributions of multiple significant variables (gestational age at birth, the presence of a vanished twin, number of infants delivered) in multiple linear regression, the adjusted mean birth weight was 166 g (95% confidence interval, 43–290 g) lower after fresh blastocyst transfer when compared with transfer of blastocysts derived from thawed bipronuclear oocytes.


Birth weights are lower in cycles with fresh blastocyst transfer after controlled ovarian stimulation than in transfers of frozen-thawed embryos in the absence of ovarian stimulation. This finding confirms similar results reported in many retrospective studies.

Clinical Trial Registration Numbers

NCT00963625 and NCT00963079.

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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.