Smaller fetal size in singletons after infertility therapies: the influence of technology and the underlying infertility

Objective: To determine whether fetal size differences exist between matched fertile and infertile women and among women with infertility achieving pregnancy through various treatment modalities. Design: Retrospective cohort study with propensity score analysis. Setting: Tertiary care center and affiliated community hospitals. Patient(s): 1,246 fertile and 461 infertile healthy women with singleton livebirths over a 10-year period. Intervention(s): Infertile women conceiving without medical assistance, with ovulation induction, or with in vitro fertilization. Main Outcome Measure(s): Birthweight; secondary outcomes included crown-rump length, second-trimester estimated fetal weight, and incidence of low birth weight and preterm delivery. Result(s): Compared with matched fertile women, infertile women had smaller neonates at birth (3,375 +/- 21 vs. 3,231 +/- 21 g) and more low-birth-weight infants (relative risk = 1.68, 95% confidence interval, 1.06, 2.67). Neonates conceived via ovulation induction were the smallest among the infertility subgroups compared with the neonates of fertile women (3,092 +/- 46 vs. 3,397 +/- 44 g). First-trimester fetal size was smaller in infertile versus fertile women (crown-rump length 7.9 +/- 0.1 vs. 8.5 +/- 0.1 mm). Within the infertility subgroups, no differences in fetal or neonatal size were found. Conclusion(s): The inherent pathologic processes associated with infertility may have a larger impact on fetal growth than infertility therapies. (Fertil Steril (R) 2011;96:1100-6. (C) 2011 by American Society for Reproductive Medicine.)