Maternal Risk and Protective Factors for Spontaneous Abortion: A Prospective Cohort Study in Mashhad, Iran

Background Spontaneous abortion is a common pregnancy complication with multifactorial etiology. Identifying maternal risk and protective factors is essential for prevention and improved prenatal care . Methods We conducted a prospective cohort study of 72,500 pregnancies registered in 2024 at health centers affiliated with Mashhad University of Medical Sciences, Iran. Pregnancies were followed to determine outcomes. Maternal characteristics, BMI, medical history, blood type, supplementation, and lifestyle factors were recorded at baseline. Multivariable logistic regression was used to identify independent risk and protective factors. Results Among 72,500 pregnancies, 5,602 ended in spontaneous abortion, yielding a cumulative incidence of 7.7%, with the majority occurring in the first trimester. Maternal age > 30 years (adjusted RR 1.45, 95% CI 1.32–1.60), prior miscarriage (RR 1.68, 95% CI 1.55–1.82), low BMI (< 18.5 kg/m²) (RR 1.37, 95% CI 1.22–1.53), hypertension (RR 1.25, 95% CI 1.10–1.42), and O-positive blood type (RR 1.15, 95% CI 1.02–1.29) were associated with increased risk. Physical work (RR 0.45, 95% CI 0.39–0.52), and supplementation with iron (RR 0.70, 95% CI 0.62–0.79), folic acid (RR 0.78, 95% CI 0.69–0.88), and vitamin D (RR 0.72, 95% CI 0.63–0.82) were protective. Abortion rates increased with maternal age and parity. Conclusion Spontaneous abortion is influenced by maternal age, reproductive history, BMI, hypertension, blood type, supplementation, and lifestyle factors. Early prenatal care and targeted interventions, including micronutrient supplementation, may reduce the risk of pregnancy loss.