Associations Between Periviable and Preterm Birth and Severe Maternal Morbidity and Mortality

Abstract

Objective: To evaluate the risk of severe maternal morbidity (SMM) and mortality associated with periviable or preterm birth. Methods: This population-based retrospective cohort study analyzed U.S. delivery hospitalizations between the fourth quarters of 2015 and 2021 by using the National Inpatient Sample database. The primary outcome was SMM and mortality risk by gestational age (20-25 weeks vs 26-36 weeks vs 37-42 weeks). Multivariable logistic regression analysis was used to assess SMM risk. Secondary outcomes included organ system-based SMM indicators and subgroup analyses by 3-week gestational age intervals (eg, 20-22 weeks, 23-25 weeks). Population attributable fraction (PAF) estimates were calculated to determine the proportion of SMM due to periviable and preterm birth. Results: Among an estimated 22,208,488 weighted births, 0.6% were periviable (20-25 weeks), 9.4% were preterm (26-36 weeks), and 90.0% were term (37-42 weeks). Severe maternal morbidity and mortality rates were highest in individuals with periviable births (4.5%, adjusted relative risk [aRR] 6.8 95% CI, 6.4-7.3, 98/100,000 delivery hospitalizations; and aRR 26.4, 95% CI, 16.7-41.9, respectively) and preterm births (2.9%, aRR 3.6, 95% CI, 3.5-3.7, 31/100,000 delivery hospitalizations; and aRR 8.7, 95% CI, 6.4-11.7, respectively) compared with term births (0.5%, 3/100,000 delivery hospitalizations). The elevated risk for SMM remained when limited to spontaneous live births in individuals without chronic comorbidities associated with iatrogenic preterm delivery (periviable: aRR 3.8, 95% CI, 3.3-4.5; preterm: aRR 1.8, 95% CI, 1.7-2.0). Individuals with periviable births had the highest risk of cardiovascular, renal, respiratory, sepsis, shock, and hemorrhagic SMM events, and those with preterm births had the highest risk of eclampsia. The PAF for SMM and maternal death was highest in individuals with preterm births (26.3%, 95% CI, 25.6-27.1; and 48.1%, 95% CI, 39.9-55.2, respectively). Conclusion: Periviable and preterm birth is associated with an increased risk of SMM and mortality, emphasizing the maternal health burden associated with early deliveries and the need for coordinated maternal-fetal risk-appropriate care.