For a study, researchers sought to evaluate the relationship between unfavorable pregnancy outcomes and allostatic load, a measure of chronic stress.

It was a secondary analysis of the prospective observational cohort study nuMoM2b (Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be). The main risk factor was dichotomous high allostatic load in the first trimester, which is indicated by 4 or more of the 12 biomarkers falling into the “worst” quadrant. The main result was a composite unfavorable pregnancy result, which included stillbirth, preterm delivery, short for gestational age (SGA), and hypertensive disorders of pregnancy (HDP). Components of the composite were secondary outcomes. With possible variables taken into account, the link between high allostatic load and unfavorable pregnancy outcomes was tested using multivariable logistic regression. The effect of allostatic load along the causative chain between racial inequalities and unfavorable pregnancy outcomes was examined using mediation and moderation methods.

A high allostatic load was seen in 34.7% of the 4,266 individuals. In 1,171 (27.5%) pregnancies, the outcomes were compositely adverse: 14.0% HDP, 8.6% preterm birth (48.0% spontaneous and 52.2% indicated), 11.0% SGA, and 0.3% stillbirth. The high allostatic load was significantly associated with a composite adverse pregnancy outcome (adjusted odds ratio [aOR] 1.5, 95% CI 1.3, 1.7), HDP (aOR 2.5, 95% CI 2.0-2.9), but not preterm birth or SGA. The association persisted after controlling for maternal age, gravidity, smoking, bleeding during the first trimester, and health insurance. The high allostatic load partially mediated the link between self-reported race and unfavorable pregnancy outcomes. The self-reported race had a different effect on the link between allostatic load and HDP but not on a composite poor pregnancy outcome, preterm delivery, or SGA.

A first-trimester allostatic load that was too high was linked to poor pregnancy outcomes, especially HDP. The partial mediator between race and unfavorable pregnancy outcomes was allostatic stress. The relationship between allostatic load and HDP varied depending on the self-reported race.