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Birthweight in infants conceived through in vitro fertilization following blastocyst or cleavage-stage embryo transfer: a national registry study



In vitro fertilization (IVF) infants have lower birthweights than their peers, predisposing them to long-term health consequences. Blastocyst transfer (BT), at day 5–6 post-fertilization, is increasing in usage, partially due to improved pregnancy outcomes over cleavage-stage transfer (CT, day 2–3). Data to date, however, have been inconclusive regarding BT’s effects on birthweight.


Participants included all US autologous, single-gestation, fresh embryo transfer cycles initiated from 2007 to 2014 that resulted in a term infant (N = 124,154) from the National Assisted Reproductive Technology Surveillance System. Generalized linear models including obstetric history, maternal demographics, and infant sex and gestational age were used to compare birthweight outcomes for infants born following BT (N = 67,169) with infants born following CT (N = 56,985) and to test for an interaction between transfer stage and single embryo transfer (SET).


Infants born following BT were 6 g larger than those born following CT (p = 0.04), but rates of macrosomia (RR 1.00, 95% CI 0.96–1.04) and low birthweight (LBW, RR 1.00, 95% CI 0.93–1.06) were not different between the groups. The interaction between SET and transfer stage was significant (p = 0.02). Among SET infants, BT was associated with 19.26 g increased birthweight compared to CT (p = 0.008).


The increase in birthweights identified following BT is unlikely to be clinically relevant, as there were no differences in rates of macrosomia or LBW. These findings are clinically reassuring and indicate that the increasing use of BT is unlikely to further decrease the on average lower birthweights seen in IVF infants compared to their naturally conceived peers.

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This work is funded by grants from the National Institutes of Health (NIH-NIMH R01MH094609, NIH-NIEHS R01ES022223, P01 ES022832) and the Environmental Protection Agency (EPA RD8354420). Funding sources had no involvement in data collection, data analysis, or generation of the manuscript.

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.

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Correspondence to Carmen J. Marsit.

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This project was approved by the Institutional Review Board at the CDC.

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The authors declare that they have no conflicts of interest.

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Litzky, J.F., Boulet, S.L., Esfandiari, N. et al. Birthweight in infants conceived through in vitro fertilization following blastocyst or cleavage-stage embryo transfer: a national registry study. J Assist Reprod Genet 35, 1027–1037 (2018).

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  • Birthweight
  • In vitro fertilization
  • Embryo transfer
  • Blastocyst
  • Cleavage-stage embryo