Adequacy of antenatal care and maternal smoking: impacts on gestational age and birth weight among preterm births in a high-risk referral cohort in Western Iran.

BACKGROUND

Preterm birth and low birth weight (LBW) are leading causes of neonatal morbidity and mortality. Adequate antenatal care (ANC) and reducing modifiable maternal risk factors such as smoking are critical, yet evidence from high-risk Middle Eastern populations remains limited.

METHODS

We conducted a retrospective cohort study of 451 preterm neonates delivered at a tertiary referral hospital in Ilam, western Iran. ANC adequacy was assessed primarily using the Kessner index and tested against alternative indices. Maternal exposures included smoking, age, hypertension, and diabetes. Logistic regression models assessed associations, with robustness tested through dose-response splines, propensity score weighting, and E-values.

RESULTS

Adequate ANC was protective, reducing odds of earlier gestational age (aOR = 0.52, 95% CI: 0.36-0.76), extremely low birth weight (RRR = 0.28, 95% CI: 0.10-0.76), and LBW overall (aOR = 0.58, 95% CI: 0.39-0.87). Maternal smoking increased risks, more than tripling ELBW (RRR = 3.75, 95% CI: 1.65-8.54) and doubling LBW (aOR = 2.18, 95% CI: 1.20-3.94). Dose-response analysis showed steadily declining LBW risk with increasing ANC utilization, plateauing beyond WHO recommendations. Findings were robust across alternative definitions and sensitivity analyses.

CONCLUSIONS

Among preterm births in this high-risk Iranian cohort, adequate ANC was associated with more favorable gestational-age and birth-weight profiles, while maternal smoking increased the severity of prematurity and fetal growth restriction.