Multiple maternal chronic conditions and risk of severe neonatal morbidity and mortality

Importance — Nearly 16% of pregnant individuals have multiple chronic conditions (MCC), and the risk of severe maternal morbidity and mortality increases in a dose-response manner with the number of preexisting conditions. However, little is known about newborn outcomes in this population.

Objective — To examine the association of the number of preexisting maternal chronic conditions, as well as the presence of MCC complexity, cardiometabolic MCC, and MCC severity, with the risk of severe neonatal morbidity or mortality (SNM-M).

Design, setting, and participants — This population-based cohort study was conducted in Ontario, Canada, among all live births from 2012 to 2021. Data were analyzed from September 2024 to November 2025.

Exposure — Maternal MCC measured in the 2 years before conception.

Main outcomes and measures — Modified Poisson regression was performed to generate adjusted relative risks (aRRs) for SNM-M by the number of chronic conditions, MCC complexity (≥3 chronic conditions in ≥3 body systems), co-occurring cardiometabolic conditions, and MCC severity marked by a prenatal hospitalization for a chronic illness. Multivariable models were adjusted for age, parity, immigration status, income quintile, and rurality.

Results — The cohort comprised 1 018 968 newborns, including 20 934 to mothers with 3 or more chronic conditions (mean [SD] maternal age, 30.0 [6.3] years), 73 768 to mothers with 2 chronic conditions (mean [SD] maternal age, 30.3 [5.8] years), 276 765 to mothers with 1 chronic condition (mean [SD] maternal age, 30.7 [5.4] years), and 647 501 to mothers with 0 chronic conditions (mean [SD] maternal age, 31.0 [5.1] years). Compared with newborns of mothers with 0 chronic conditions, the aRR for SNM-M increased in a dose-response fashion in newborns of mothers with 1 (1.26; 95% CI, 1.24-1.28), 2 (1.58; 95% CI, 1.54-1.62), and 3 or more (2.01; 95% CI, 1.94-2.09) chronic conditions. The aRRs were also increased with complex MCC (1.97; 95% CI, 1.88-2.06), cardiometabolic MCC (2.67; 95% CI, 2.24-3.19), and severe MCC (3.11; 95% CI, 2.55-3.79).

Conclusions and relevance — In this study, risks of SNM-M increased with an increasing number of preexisting maternal chronic conditions. These findings suggest that women and adolescents with MCC may benefit from preconception counseling to optimize chronic disease management, monitoring in pregnancy for earlier identification of complications, and enhanced newborn supports.