Figure 4. Suggested developmental strategies associated with imbalances between fetal nutrient demand and materno-placental nutrient supply.

The distribution of placental blood flow is based on nutritional status, with ductus venosus liver shunting and brain-sparing if the fetal demand for essential nutrients exceeds placental supply (A). However, when supply of conditionally essential nutrients is inadequate, the strategy is to prioritize liver blood flow, enabling hepatic nutrient interconversions and the synthesis of fatty acids required for fat deposition; in this circumstance fat deposition is prioritized as it is needed for neonatal thermoregulation and as a buffer for brain development during subsequent periods of limited nutrient supply (B). In environments less affluent than those now prevalent in developed populations, facilitated placental transfer mechanisms evolved for glucose and other nutrients to enable materno-placental nutrient supply to meet fetal nutrient demand, resulting in optimal fetal body composition (C); however, in circumstances of nutrient excess (such as maternal adiposity and impaired glucose tolerance (IGT)) these mechanisms also lead to prenatal fat deposition (D).