OBJECTIVE: A low mean birth weight is a constant finding in pregnancies of women with homozygous sickle cell disease. The factors responsible are largely unknown and have now been investigated in an 11-year retrospective analysis. METHODS: Records for 126 pregnancies of mothers with homozygous sickle cell disease and 126 pregnancies of control women with an AA phenotype, matched according to age and date of delivery, were examined. Events during pregnancy and outcomes of pregnancy were recorded. RESULTS: Pregnancy outcomes for mothers with homozygous sickle cell disease confirmed the lower birth weight, gestational age, and placental weight. A low birth weight in infants of mothers with homozygous sickle cell disease was strongly related to gestational age and placental weight and weakly related to reticulocyte counts and a history of preeclampsia in univariate analyses, but only gestational age and placental weight remained significant in multivariate analyses. No relationships were seen with maternal age, parity, anthropometric features, other hematologic features (hemoglobin levels, fetal hemoglobin levels, mean cell volume, and alpha-thalassemia), pregnancy-induced hypertension, or prepartum hospital admissions (expressed as number or total days). Compared with Jamaican standards, birth weight was affected more than head circumference or length in infants of mothers with homozygous sickle cell disease, indicating asymmetric growth retardation, which occurred for 27% of boys and 38% of girls (compared with 4% and 9%, respectively, among infants of control mothers). CONCLUSIONS: A chronic condition such as homozygous sickle cell disease might have been expected to cause symmetric growth retardation throughout pregnancy. The finding of asymmetric retardation might indicate adverse factors emerging late in pregnancy and might have relevance for the poor pregnancy outcomes in such mothers.