Maternal age-specific drivers of severe maternal morbidity

Abstract

Background: The maternal age influences the risk of adverse pregnancy outcomes, including severe maternal morbidity. However, the leading drivers of severe maternal morbidity may differ between the maternal age groups.

Objective: To compare the contribution of different risk factors to the risk of severe maternal morbidity between various maternal age groups and estimate their population-attributable risks.

Study design: This was a retrospective, population-based cohort study of all US live births from 2012 to 2016 using birth certificate records. The demographic, medical, and pregnancy factors were compared between the 4 maternal age strata (<18 years, 18-34 years, 35-39 years, and ≥40 years). The primary outcome was composite severe maternal morbidity, defined as having maternal intensive care unit admission, eclampsia, unplanned hysterectomy, or a ruptured uterus. Multivariate logistic regression estimated the relative influence of the risk factors associated with severe maternal morbidity among the maternal age categories. Population-attributable fraction calculations assessed the contribution of the individual risk factors to overall severe maternal morbidity.

Results: Of 19,473,910 births in the United States from 2012 to 2016, 80,553 (41 cases per 10,000 delivery hospitalizations) experienced severe maternal morbidity. The highest rates of severe maternal morbidity were observed at the extremes of maternal age: 45 per 10,000 at <18 years (risk ratio, 1.31; 95% confidence interval, [1.16-1.48]) and 73 per 10,000 (risk ratio, 2.02; 95% confidence interval, [1.96-2.09]) for ≥40 years. In all the age groups, preterm delivery, cesarean delivery, chronic hypertension, and preeclampsia were significantly associated with an increased adjusted relative risk of severe maternal morbidity. Cesarean delivery and preeclampsia increased the severe maternal morbidity risk among all the age groups and were more influential among the youngest mothers. The risk factors with the greatest population-attributable fractions were non-Hispanic Black race (5.4%), preeclampsia (10.9%), preterm delivery (29.4%), and cesarean delivery (38.1%). On the basis of these estimates, the births occurring in mothers at the extremes of maternal age (<18 and ≥35 years) contributed 4 severe maternal morbidity cases per 10,000 live births. Preterm birth and cesarean delivery contributed 12 and 15 cases of severe maternal morbidity per 10,000 live births, respectively.

Conclusion: Both adolescent and advanced-age pregnancies have an increased risk of severe maternal morbidity. However, there are age-specific differences in the drivers of severe maternal morbidity. This information may allow for better identification of those at a higher risk of severe maternal morbidity and may ultimately aid in patient counseling. KEY WORDS: adolescents, advanced-age pregnancy, maternal morbidity, population-attributable fraction.