The long-chain polyunsaturated fatty acids docosahexaenoic acid (DHA, omega-3) and arachidonic acid (AA, omega-6) are rapidly deposited in brain and retina during early growth. Meta-analyses of randomised controlled trials demonstrate that the provision of oils with DHA or with DHA and eicosapentaenoic acid in pregnancy markedly reduce premature births <34 weeks by 31% in the total population and by 61% in at-risk pregnancies, along with a slight increase in pregnancy duration and infant birth size and without relevant adverse effects up to 1 g DHA/day. The human fetus is supplied with preformed DHA by placental transfer that we demonstrated with stable isotope studies and that seems to be mediated by specific transfer proteins. Several studies indicate that DHA supply to pregnant and lactating women and to infants can improve the child’s visual development, fine motor function, social skill scores, language discrimination and verbal IQ up to school age. Maternal DHA supply during pregnancy also modulates the infant’s immune response at birth, yielding a pattern compatible with lower allergy risk. Evidence-based recommendations on dietary fat supply for pregnant and lactating women developed with support from the European Commission conclude that pregnant and lactating women should approach an average DHA intake of at least 200 mg DHA/day, which can be provided by one to two meals of ocean fish per week, including fatty fish. Women who do not achieve this level of regular fish consumption should consider using DHA supplements. DHA should be considered a conditionally essential substrate that should be supplied to pregnant and lactating women to support optimal pregnancy outcomes and child development.