Figure 1. Scheme of the sources of cholesterol from different times of gestation. A. From about 5-10 weeks of gestation, the primary source of nutrition for the embryo/fetus is from uterine gland secretions in the form of lipid droplets (dark blue circles). There is a small amount of maternal lipoproteins (green and orange circles) that is also present in the exocoleum cavity from leakage from spiral arteries. The lipids diffuse into the yolk sac cavity and are taken up by the apical side of the yolk sac’s endoderm cells via receptor- and receptor-independent mechanisms. The cholesterol is released from other components in lysosomes and repackaged into APOB-containing lipoproteins (and perhaps other lipoproteins) and secreted into the vitteline vessels which combine with the fetal circulation in the mid-gut. B. From 10 weeks of gestation to parturition, the fetus obtains its cholesterol from the maternal circulation in the placenta. The maternal cholesterol-carrying lipoproteins are taken up by the apical side of multi-nucleated syncytialized trophoblasts, is released from other components of the lipoproteins in lysosomes, and transported to the basolateral side of the trophoblasts. The cholesterol exits the trophoblasts to the stroma or cells within the stroma, is taken up by the fetal endothelial cells, is processed or transported to the opposite side where the cholesterol exits the cells. The routes of exit from the trophoblasts or endothelial cells are discussed in Figure 2.