Difference in birth weight of consecutive sibling singletons is not found in oocyte donation when comparing fresh versus frozen embryo replacements

With the use of oocyte donation-originated siblings, and controlling for potential laboratory and clinical confounders, similar birth weight and duration of gestation were observed with both fresh and frozen embryos.

Daniela Galliano, M.D., Ph.D., Nicolás Garrido, Ph.D., M.Sc., Vicente Serra-Serra, M.D., Ph.D., Antonio Pellicer, M.D., Ph.D.

Volume 104, Issue 6, Pages 1411-1418


First, to assess if there are any differences in birth weight or gestational length in newborns from egg-donation pregnancies delivering singletons, originating from either fresh or frozen-thawed embryos when they were developed and delivered within the same mothers. Second, to determine if there are any clinical, phenotypic, or laboratory factors influencing this relationship, including the origin of the oocyte (same or different donor), the order of the children (first fresh or first frozen-thawed embryo transfer), the embryo freezing technique (vitrification or slow freezing), the in vitro embryo culture length, and the duration that embryos remained frozen.

Retrospective cohorts study.

University-affiliated infertility centers.

A total of 360 women undergoing oocyte donation (OD), delivering (>28 weeks) at least two babies, each one from a single pregnancy, originating from at least one fresh and one frozen-thawed embryo transfer, controlling maternal and laboratory characteristics, to test the effect of embryo freezing on children size (n = 731).


Main Outcome Measure(s):
Birth weight, gestational age, weight percentile, being large for gestational age (LGA), small for gestational age (SGA), size out of normal range (ONR = LGA + SGA), and macrosomy.

From fresh versus thawed embryos, respectively, mean birth weight of children was 3,183.7 g versus 3,226.4 g, gestational age was 272.1 days versus 268.8 days, and mean weight percentiles were 47.6 versus 50.1. The proportions and corresponding odds ratios (ORs) from fresh versus thawed embryos, respectively, were for LGA 13.6% versus 11.3% (OR 0.81), for SGA 9.4% versus 12.5% (OR 1.37), for ONR 23.1% versus 23.8% (OR 1.04), and for macrosomy 0.3% versus 0.8% (OR 3.1). After adjusting for clinically relevant variables, the ORs were for LGA 0.96, for SGA 1.40, for ONR 1.20, and for macrosomy not computable. None of the stated measures were significantly different. Also, independent analyses run on the origin of the oocytes, cryopreservation technique, cleavage stage of the embryos, and time that embryos remained frozen did not reveal any significant trends.

This study comparing siblings from OD cycles, and eliminating the independent variables that affect early events in pregnancy, revealed no difference in duration of gestation and live birth weights between fetuses obtained after the replacement of fresh or frozen embryos. Moreover, no clinical, phenotypic, or laboratory factors appeared to be relevant, once statistically controlled.

  • Jason M. Franasiak

    An interesting study which finds that no differences in gestational age at delivery or birth weight exists between fresh or frozen embryos. This adds to the fresh ET vs. frozen ET debate as it suggests many of the differences seen are related to the endometrium and impaired placentation rather than changes to the embryo seen during cryopreservation.

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