V1iii: Factors which influence transfer of nutrients across placenta to foetus

Nutritional Requirements of Growing Fetus

By 3^rd trimester of pregnancy, maternal caloric intake only increases 340-450kcal/d

However, as gestational age increases, the energy needs for fetal development in increase markedly

Fetal growth is a direct consequence of nutrient availability & placenta’s ability to transport these from maternal circulation to fetus:

Placental arrangement confers no mixing of fetal w maternal blood

2 layers of placenta which substrates must cross

1. Syncytiotrophoblasts (SCTB) on maternal side
2. Fetal Capillary endothelium (selective permeability dependant on size & charge)

Pregnancy = natural state of maternal insulin resistance

Immature fetus = minimal gluconeogenesis

Thus, glucose availability to fetus depends on concentration in maternal circulation

Family of GLUT transporters transfer glucose to fetus

GLUT1 = most abundant and increase expression w gestational age

Uptake relies on active transport (ATP)

Plasma [a-acids] are higher in fetus cf mother

Two systems: System A & System L

System A = sodium dependant

System L = sodium independent (relies on glucose)

Lipids in maternal circulation circulate as triglycerides

Broken down by placental lipases into Phospholipids + Cholesterol

FFA transport proteins then take up FAs

Integral to cell membrane development & synthesis of steroid hormones

Specific transporters for LDL, HDL & VLDL on placenta

Cholesterol transported through specific ‘binding cassette transporter A1 & G1’ on endothelial fetal vessels