Abuse during pregnancy is considered to be a potentially modifiable risk factor for low birth weight (LBW). We conducted a systematic review and meta-analysis to determine the strength of association between physical, sexual or emotional abuse during pregnancy and LBW. We selected papers for review from an electronic search of MEDLINE (1966-1999), CINAHL (1982-1997) and the Cochrane Library. We retrieved articles using the following MeSH headings and keywords: "infant low birth weight," "fetus," "perinatal care," "pregnancy," "prenatal care," "infant mortality," "violence," "battered women," "spouse abuse," "infant morbidity," "antenatal" and "neonatal." When necessary, we contacted authors to obtain data that were not included in the published material. We analyzed the methodological quality of each eligible study and selected those of the highest quality for meta-analysis. We reviewed 14 studies, of which 8 were selected for meta-analysis. Using a fixed-effects model, we found that women who reported physical, sexual or emotional abuse during pregnancy were more likely than nonabused women to give birth to a baby with LBW (odds ratio 1.4, 95% confidence interval 1.1-1.8). Abuse may be part of a complex interaction of factors that contribute to LBW.