Are risk factors the same for small for gestational age versus other preterm births?

OBJECTIVES: This article explores whether the impact of social and demographic risk factors for preterm birth differs for small for gestational age preterm births versus other preterm births, STUDY DESIGN: This was a European case control study of the determinants of preterm birth (4700 cases and 6460 controls). Small for gestational age and non-small for gestational age preterm births were compared with a control group of term births; relationships were explored further by stratifying preterm births into subgroups by mode of onset, the presence of hypertension, and gestational age. RESULTS: Of the social and demographic risk factors for preterm birth identified in this sample, high maternal age, smoking, and low and high maternal body mass index have a stronger effect on small for gestational age preterm births. In contrast, obstetric history, maternal education, and marital status have similar effects regardless of birth weight. Hypertension during pregnancy is strongly associated with small for gestational age preterm birth and contributes to an explanation of observed differences. CONCLUSIONS: These results underline the importance of considering fetal growth restriction in the analysis of risk factors for preterm birth.