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. Author manuscript; available in PMC: 2019 Apr 1.
Published in final edited form as: Am J Obstet Gynecol. 2017 Dec 29;218(4):433.e1–433.e10. doi: 10.1016/j.ajog.2017.12.223

Table 3.

Rates of macrosomia and low birthweight (LBW) among infants conceived with Assisted Reproductive Technology following fresh and frozen/thawed embryo transfer, and relative risks for frozen/thawed versus fresh embryo transfer. National ART Surveillance System (NASS).

Fresh Embryo Transfer Frozen/Thawed Embryo Transfer
Normal Birthweight (>2,500 to ≤4,000 grams)
 N (%) 110491 (88.9) 47230 (84.5)
Low Birthweight (1500–2500 grams)
 N (%) 3855 (3.1) 886 (1.6)
 RR (95% CI) Ref. 0.51 (0.48–0.55)
 aRR (95% CI) Ref. 0.52 (0.48–0.56)
Macrosomic (>4000 grams)
 N (%) 9940 (8.0) 7782 (13.9)
 RR (95% CI) Ref 1.74 (1.69–1.79)
 aRR (95% CI) Ref. 1.70 (1.64–1.76)

RR= relative risk; aRR = adjusted relative risk (adjusted for infertility diagnosis, maternal and paternal race, obstetric history, infant sex, year of transfer, gestational age, and maternal age)