Neonatal hair cortisol and birth outcomes: An empirical study and meta-analysis.

OBJECTIVE: Prenatal stress physiology is often posited as a predictor of birth outcomes, including gestational age at birth and birthweight. However, research has predominantly relied on indicators in the maternal system, with few studies examining hormones of the fetal system. The current study focuses on fetal cortisol in the third trimester, as measured in neonatal hair, as a biological factor that might associate with birth outcomes (gestational age at birth and birthweight). We report findings from two studies: a longitudinal cohort (Study 1), and a meta-analysis of the existing literature (Study 2).

METHODS STUDY: Hair was collected for cortisol analysis from 168 neonates (55.95% female) shortly after birth. Gestational age at birth and birthweight were abstracted from medical records.

METHODS STUDY: An exhaustive search of four databases was conducted, yielding 155 total studies for screening. Papers reporting neonatal hair cortisol (collection <2 weeks postpartum) and birth outcomes among human neonates were retained for analysis, including Study 1 results (k = 9).

RESULTS STUDY: Higher neonatal hair cortisol was related to longer gestation, r = .28, p < .001, and higher birthweight, r = .16, p = .040. Sex did not moderate either association.

RESULTS STUDY: Across the nine studies, higher neonatal hair cortisol predicted both longer gestation, r = .35, p < .001, 95% CI [0.24,0.45] and higher birthweight, r = .18, p = .001, 95% CI [0.07,0.28]. Neonatal sex did not moderate these associations.

CONCLUSIONS: Fetal cortisol exposure in the third trimester plays a role in normative maturation of the fetus and findings reveal that higher cortisol is associated with positive birth outcomes.