The associations of parity and maternal age with small-for-gestational-age, preterm, and neonatal and infant mortality: a meta-analysis

Background: Previous studies have reported on adverse neonatal outcomes associated with parity and maternal age. Many of these studies have relied on cross-sectional data, from which drawing causal inference is complex. We explore the associations between parity/maternal age and adverse neonatal outcomes using data from cohort studies conducted in low-and middle-income countries (LMIC). Methods: Data from 14 cohort studies were included. Parity (nulliparous, parity 1-2, parity >= 3) and maternal age (< 18 years, 18-< 35 years, >= 35 years) categories were matched with each other to create exposure categories, with those who are parity 1-2 and age 18-< 35 years as the reference. Outcomes included small-for-gestational-age (SGA), preterm, neonatal and infant mortality. Adjusted odds ratios (aOR) were calculated per study and meta-analyzed. Results: Nulliparous, age < 18 year women, compared with women who were parity 1-2 and age 18-< 35 years had the highest odds of SGA (pooled adjusted OR: 1.80), preterm (pooled aOR: 1.52), neonatal mortality (pooled aOR: 2.07), and infant mortality (pooled aOR: 1.49). Increased odds were also noted for SGA and neonatal mortality for nulliparous/age 18-< 35 years, preterm, neonatal, and infant mortality for parity >= 3/age 18-< 35 years, and preterm and neonatal mortality for parity >= 3/>= 35 years. Conclusions: Nulliparous women < 18 years of age have the highest odds of adverse neonatal outcomes. Family planning has traditionally been the least successful in addressing young age as a risk factor; a renewed focus must be placed on finding effective interventions that delay age at first birth. Higher odds of adverse outcomes are also seen among parity >= 3/age >= 35 mothers, suggesting that reproductive health interventions need to address the entirety of a woman's reproductive period.