In Sweden, approximately 300 infants are born extremely preterm i.e. before 28 gestational weeks yearly. With modern neonatal care, infants born as early as at 23-24 weeks of gestation, in the second trimester of gestation, have more than 50% chance of survival. The third trimester is a period of intense growth and differentiation of the central nervous system (CNS) of which the retina is a part, with rapid formation of synapses and dendritic spines and development of retinal photoreceptor cells. During this fetal time period AA and DHA are selectively transferred from the mother to her fetus and blood fractions of DHA increase above maternal values. AA fractions are high, twice those of the mother, from at least 24 weeks of gestation. After very preterm birth, the fractions of AA and DHA fall. In utero glucose, not lipid is the main source of energy and the LCPUFAs transferred during the third trimester play important structural and functional roles in membranes of the central nervous system and most other organs.