Maternal prenatal stress and infant birth weight and gestational age: A meta-analysis of prospective studies

•Maternal prenatal stress (MPS) is linked to infant birth weight and gestational age.•Research results have varied greatly.•This meta-analysis examines several moderators of this relation.•Greater effect sizes are found when stress is defined as pregnancy specific.•Effect size is also moderated by national context and risk.

The present meta-analysis addresses the relation between maternal prenatal stress (MPS) and infant birth weight and gestational age in 88 prospective studies (N = 5,889,930) published between 1970 and 2012. The results suggest that this relation is significant (d = −.12; 95% CI: −.17, −.08). Three factors moderated overall effect size: 1) The type of MPS assessment: Pregnancy-related stress and anxiety yielded greater effect sizes (d = −.25; 95% CI:−.32, −.18; k = 22) than trait-based assessments (d = −.13; 95% CI:−.22, −.03; k = 22), life event measures (d = −.03; 95% CI:−.05, −.01; k = 55) or exposure to natural disasters (d = −.11; 95% CI:−.21, −.02; k = 24). Both state (d = −.14; 95% CI:−.25, −.03; k = 82) and trait MPS assessments yielded greater effect sizes than life event measures of stress; 2) studies involving high-risk samples tended to yield greater associations (d = −.26; 95% CI: −.44, −.09; k = 16) than those involving low-risk groups (d = −.08; 95% CI: −.13, .04; k = 72); 3) studies conducted outside of North America (d = −.01; 95% CI: −.14, −.06; k = 50) or Europe (d = −.06; 95% CI: −.12, −.01; k = 31) yielded greater effect sizes (d = −.70; 95% CI: −1.14, −.24; k = 7). Discussion focuses on the need to identify the kinds of stress most related to birth outcome, as well as the biological and environmental contexts that serve to mediate this relation.