BACKGROUND: Intimate partner violence is a major public health problem. It occurs commonly in pregnancy, resulting in adverse events for women and their fetus or children. The objective of this study was to examine the association between intimate partner violence and very preterm birth. METHODS: This population-based, case-control study was conducted in Victoria, Australia, from 2002 to 2004. Interviews were conducted with 603 women who had a singleton very preterm birth (20-31 weeks' gestation), 770 women who had a singleton term birth (37 or more completed weeks' gestation), 139 women who had a very preterm twin birth, and 214 women who had a term twin birth. Intimate partner violence was measured using the Composite Abuse Scale, and questions were also asked about fear of partners and violence from others. RESULTS: Prevalence of intimate partner violence in the past 12 months was 14.9 percent in singleton case women, 11.7 percent in singleton control women, 9.5 percent in twin case women, and 14.7 percent in twin control women. Fear of a previous partner and reporting similar violence experience with someone else were more likely in singleton births (AOR = 1.36; 95% CI 1.03, 1.79) and (AOR = 1.44; 95% CI 1.12, 1.86), respectively. No differences between twin case women and twin control women were observed. When the precipitating cause of very preterm birth was investigated, antepartum hemorrhage was significantly associated with intimate partner violence and all its subscales. CONCLUSIONS: The heterogeneity of causes of very preterm birth may explain the lack of association found with intimate partner violence in pregnancy. Pregnant women have a significant risk of intimate partner violence, which should be a serious concern for all care providers.