Preterm birth accounts for more than 85% of all perinatal complications and deaths. There are many short- and long-term consequences of being born too soon. These infants often require intensive care and are at increased risk of early morbidities often with life-long sequelae. Approximately 50% of all preterm births have unknown or unclear causes, and there are no effective primary prevention strategies in widespread clinical use. Epidemiological studies have observed an increased length of gestation in populations with high fish consumption. These findings have led to randomised controlled trials of omega-3 (n-3) long-chain polyunsaturated fatty acid (LCPUFA) supplementation which show that these dietary agents may delay the timing of birth and may have value as a prophylactic intervention in some women. This review presents the available evidence and discusses the relationship between prenatal n-3 LCPUFA supplementation during pregnancy and the incidence of preterm birth.