Abstract
BACKGROUND: Maternal age and cohabitation (women living with a partner in marriage or in a common-law relationship) are known to be associated with adverse birth outcomes. However, how these two factors jointly contribute to birth outcomes is not well understood, particularly among minor mothers. METHODS: All live births that occurred in Argentina 2001-2021 (N=13 807 028) were used to estimate the prevalence of births to minor mothers (<18 years). In analyses restricted to mothers aged ≤24 years (N=5 159 231), multinomial and binary logistic models were used to obtain crude and adjusted ORs (aOR) for the joint association between cohabitation status and maternal age groups (minors: ≤15 and 16-17 years, and young adults: 18-19 years and 20-24 years) with preterm birth (PTB), small-for-gestational age (SGA) groups and repeat birth. RESULTS: Minor mothers accounted for 6% of all births (n=791 731), lived in poor regions and were more likely to have incomplete primary education and no employment. Among mothers aged <24 years, adverse outcomes jointly varied according to cohabitation status and maternal age (p value for interaction <0.001 in all models). Adverse outcomes were more frequent among minors. Compared with non-cohabiting mothers aged 20-24 years, cohabiting mothers aged 20-24 years had lower odds of very PTB (0.82% vs 1.19%), moderately PTB (7.15% vs 6.33%), extreme SGA (1.98% vs 2.56%) and moderately SGA (3.63% vs 4.48%, respectively). However, compared with non-cohabiting mothers aged 20-24 years, cohabiting minor mothers, particularly those aged ≤15 years had higher odds of very PTB (24-31 gestation weeks) (AOR: 1.86 (95% CI 1.76, 1.97)), moderately PTB (32-36 weeks) (AOR: 1.53 (95% CI 1.49, 1.57)), extreme SGA (<3rd percentile) (AOR: 1.10 (95% CI 1.06, 1.14)) and moderately SGA (3rd to <10th percentile) (AOR: 1.05 (95% CI 1.01, 1.08)). CONCLUSIONS: The cohabitation advantage among young adults was not observed among minor mothers, particularly those aged ≤15 years.