Downward percentile crossing as an indicator of an adverse prenatal environment

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Background: Postnatal health sequelae of low birth weight have been attributed to ‘poor fetal growth’ from inferred adverse prenatal environments; risks augmented by infant growth rates. Identifying prenatal growth-restricting events is essential to clarify pathways and mechanisms of fetal growth.Aim: The specific aim of this investigation was to examine whether an episode of preterm labor may compromise fetal growth.Subjects and methods: Fetal size at the end of the second trimester and birth were compared among women with uncomplicated pregnancies (n = 3167) and those who experienced an episode of preterm labor (<37 weeks) and subsequently delivered at term (≥37 weeks, n = 147). Fetal weight estimated from ultrasound measures, and changes in weight standard scores across the third trimester investigated significant centile crossing (>0.67 standard deviation score change).Results: Fetuses delivered at term after an episode of preterm labor were smaller at birth relative to their peers than at the end of the second trimester, and were 47% more likely to experience clinically significant downward centile crossing (p < 0.05) than their peers (OR 1.47, 95% CI 1.04–2.07).Conclusion: An episode of preterm labor may signal an adverse prenatal environment for term-delivered neonates. Epidemiologically silent events in the natural history of pregnancy are an understudied source of fetal growth compromise as inferred by small birth size among peers.