Effects of maternal hypertension on the fetus
Any form of hypertension during pregnancy has a significant effect on fetal growth and survival. This happens because of the marked reduction in the mother's blood volume, which will in turn reduce the blood supply from the endometrial arteries into the placenta. The endometrial arteries bring the mother's blood into the placenta, delivering oxygen from her lungs and nutrients from her digestive system to the fetus. (You can see them if you look back at Figure 5.5 in Study Session 5.)
If the maternal blood flow into the placenta is reduced, what effect will this have on fetal development?
The transfer of oxygen, nutrients and fluids to the baby will be reduced, so it will not develop normally. Fetal growth is likely to be restricted (hypertension during pregnancy is one of the common causes of intra-uterine growth restriction, IUGR).
The amount of amniotic fluid surrounding the fetus will also be much less than normal, because the blood flow to the baby's kidneys is reduced, so it makes less urine. In late pregnancy, most of the amniotic fluid comes from the baby's urine. The fetus may die due to deficiency of oxygen and nutrients, or due to significant reduction of amniotic fluid. If the fetus lives very long in the uterus with a reduced oxygen supply, the growing brain is very likely to be dangerously affected. As a result, if the baby is born alive and survives early childhood, mental retardation can appear when it is older.
The fetus may also die because the placenta gets aged too early and the blood supply is inadequate, so there can be early separation of the placenta from the wall of the uterus. (Early detachment is called placental abruption and you will learn all about it in Study Session 21. Preterm labour may begin spontaneously (Study Session 17), and the mother's life can also be at risk due to severe placental abruption where much blood may be lost.