Recurrence of fetal growth restriction in singleton and twin gestations.

Objective. Patterns of recurrence of restricted fetal growth provide important insights to understand the relative contributions of genetic versus environmental influences. Although there is evidence of increased tendency of small for gestational age (SGA) births to recur, whether similar patterns of recurrence in twins among women that delivered a prior singleton SGA birth remains poorly studied. Methods. We used Missouri's maternally-linked data (1978-1997), and restricted the analysis to women that delivered their first two consecutive live births. SGA (birthweight <10th and <5th centile for gestational age) recurrence was examined in two distinct analyses: women that delivered their first two singleton live births (n = 305,654) and those that delivered their first singleton live birth followed by twin live births (n = 8594). Sib-sib pairwise odds ratio (pOR) were estimated from bivariate logistic regression with robust variance estimation after adjustments for confounders. Results. Risks of SGA were 24.3% and 6.1% in the second singleton birth among women with and without a previous singleton SGA, respectively (pOR 3.9, 95% CI 3.7-4.0). The corresponding risks among twins with and without a previous singleton SGA birth were 16.9% and 6.7%, respectively (pOR 2.3, 95% CI 1.8-2.8). In the singleton-singleton cohort, the highest recurrence risk for SGA occurred around the same gestational age window as the first singleton SGA birth. These associations were stronger for more severe forms of SGA (<5th centile). Conclusions. The likelihood of SGA to recur within sibships is strong, with varying magnitude of risks between singleton-singleton and singleton-twin births. [ABSTRACT FROM AUTHOR]