To investigate the relations of maternal diet and smoking during pregnancy to placental and birth weights at term. Design Prospective cohort study. Setting District general hospital in the south of England. Participants 693 pregnant nulliparous white women with singleton pregnancies who were selected from antenatal booking clinics with stratified random sampling.
Main outcome measures Birth and placental weights at term.
Results Placental and birth weights were unrelated to the intake of any macronutrient. Early in pregnancy, vitamin C was the only micronutrient independently associated with birth weight after adjustment for maternal height and smoking. Vitamin C, vitamin E, and folate were each associated with placental weight after adjustment for maternal characteristics. No nutrient late in pregnancy was associated with either placental or birth weight. Conclusions Concern over the impact of maternal nutrition on the health of the infant has been premature.