Preterm delivery: effects of socioeconomic factors, psychological stress, smoking, alcohol, and caffeine.

OBJECTIVE: To examine the relation between preterm birth and socioeconomic and psychological factors, smoking, and alcohol, and caffeine consumption.

DESIGN: Prospective study of outcome of pregnancy.

SETTING: District general hospital in inner London.

PARTICIPANTS: 1860 consecutive white women booking for delivery; 1513 women studied after exclusion because of multiple pregnancy and diabetes, refusals, and loss to follow up.

MEASUREMENTS: Gestational age was determined from ultrasound and maternal dates; preterm birth was defined as less than 37 completed weeks. Independent variables included smoking, alcohol and caffeine consumption, and a range of indicators of socioeconomic status and psychological stress.

MAIN RESULTS: Unifactorial analyses showed that lower social class, less education, single marital status, low income, trouble with "nerves" and depression, help from professional agencies, and little contact with neighbours were all significantly associated with an increased risk of preterm birth. There were no apparent effects of smoking, alcohol, or caffeine on the length of gestation overall, although there was an association between smoking and delivery before 32 weeks. Cluster analysis indicated three subgroups of women delivering preterm: two predominantly of low social status and a third of older women with higher social status who did not smoke. Mean gestational age was highest in the third group.

CONCLUSIONS: Adverse social circumstances are associated with preterm birth but smoking is not, apart from an association with very early births. This runs counter to findings for fetal growth (birth weight for gestational age) in this study, where a strong effect of smoking on fetal growth was observed but there was no evidence for any association with psychosocial factors.