Maternal age and parity influences on health outcomes: a multivariable regression analysis of mothers and infants.

BACKGROUND: Adverse pregnancy and birth outcomes remain significant public health challenges, particularly in low- and middle-income countries (LMICs). Maternal age and parity are recognised as key factors, yet their combined influence on maternal and infant outcomes is less understood, especially in LMICs. OBJECTIVES: We investigated the combined effects of maternal age and parity on maternal health risks, including body mass index (BMI), gestational diabetes mellitus (GDM), and hypertension, as well as infant birth outcomes, namely birth weight, length, and gestational age, in an urban South African cohort. METHODS: This study used data from 830 pregnant women (aged 18-44) enrolled in the Soweto First 1000 Days (S1000) longitudinal cohort. Group comparisons were conducted using ANOVA, chi-square, or Kruskal-Wallis tests. Multivariable Linear and logistic regression models assessed associations between age-parity and outcomes, adjusting for sociodemographic factors. Analyses were conducted in StataSE 18; p < .05 was considered significant. RESULTS: Mothers > 23 years, ≥ 1 child had higher BMI (28.6 kg/m², p < .001) and increased likelihood of hypertension (44.1%, p < .001), and GDM (7.4%, p = .012). Nulliparous women showed greater gestational weight gain (0.39 kg/week, p < .001) and an increased likelihood of having low birth weight (2960 g vs. 3185 g, p = .002), small for gestational age (SGA) (22.9%, p = .009), and shorter birth length infants (z = - 0.29, 95% CI: [- 0.57 to - 0.01], p = .04). Infants of mothers ≤ 23 years, ≥ 1 child had higher birth weight (β = 0.60, 95% CI: [0.32-0.88]; p < .001) and length z-scores (95% CI: [0.01-0.97], p = .046). Hypertension (β = -0.99, 95% CI: [- 1.52 to - 0.45], p < .001) and GDM (β = -0.57, 95% CI: [- 1.10 to - 0.04], p = .036) were associated with shorter gestational age. CONCLUSION: Maternal age and parity were associated with distinct risks to maternal and infant health. These findings support the need for more targeted, risk-based antenatal strategies in LMICs.