Quantitative meta-analysis of maternal prenatal salivary cortisol and newborn birthweight does not identify effect of fetal sex

Abstract

Background: Heightened concentration of maternal cortisol is a frequently proposed mechanism linking adverse maternal environments with poor birth outcomes, including birth weight. It is commonly hypothesized that prenatal exposures have sexually dimorphic effects on fetal development, however few studies have assessed the effects of fetal sex on the relationship between maternal cortisol and birth outcomes.

Methods: In a previous systematic review and meta-analysis we obtained data from authors of included studies to calculate trimester-specific correlations between maternal prenatal salivary cortisol and newborn birth weight. Given that this data was well-poised to address the unknown effects of fetal sex on the relationship between maternal cortisol and birth outcomes, we contacted authors a second time with request to unblind sex into the correlations. An updated database search was conducted to identify potentially relevant articles published within 2018 and two additional articles were included.

Results and discussion: Eleven studies with a total of 2236 maternal-fetal dyads demonstrated negative correlations for both males, -0.15 (95% CI -0.24 to -0.06, I² = 98.5%, p < 0.001) and females -0.21 (95% CI -0.25 to -0.17, I² = 93.3%, p < 0.001). Sex difference were not statistically significant, p = 0.62. Despite greater exposure to cortisol and lower birth weight among females, the association did not differ by sex.

Keywords: Birth weight; Cortisol; Fetal sex; Growth strategies; Pregnancy.