The blood pressure is measured at every antenatal visit because raised blood pressure may be dangerous for mother and baby. Women who have a family history of hypertension or those who are hypertensive before pregnancy may experience a rise in blood pressure. Very rarely kidney disorders may be associated with hypertension. Mild hypertension (under 140/100 mm of mercury) poses minimal risk because the lining of the blood vessels is not damaged, but levels above this may be very dangerous.
Pre-eclampsia is specific to pregnancy, and thus is also known as pregnancy induced hypertension. It is characterized by hypertension, OEDEMA and FLUID RETENTION, and protein in the urine. In its mild state raised blood pressure (still under 140/100mm of mercury) is the only sign, but it may become more serious and blood pressure may rise above 160/110 mm of mercury and protein may appear in the urine in great quantities. Severe pre-eclampsia brings on widespread changes in the endothelial lining of blood vessels throughout the body; if untreated it may progress to life-threatening eclampsia with convulsions. As the severity of the condition increases it may exert a number of effects, altering kidney and liver function, the blood clotting system and brain function and bringing on convulsions. There is also a risk of placental insufficiency and the baby's growth may be affected - in sever cases there may be a threat to foetal well-being. The cause of pre-eclampsia is unknown. It is more common in a first pregnancy, with twins and in women whose nutrition and vitamin and mineral status is not optimal and it usually disappears within weeks of the birth. It may be related to an inappropriate response by the mother's immune system to the placenta or the baby. It may also be related to the way the placenta implants in the uterus early in pregnancy. Poor implantation is associated with placental insufficiency, small babies and pre-eclampsia. It may be possible to identify reduced blood flow in the mother’s uterine arteries using a doppler technique at the 20 week ultrasound. Increased resistance to blood flow in the uterine arteries may predict the risk of pre-eclampsia developing later in pregnancy.
Essential hypertension in women who enter pregnancy with a raised blood pressure may run in the family. Provided the elevation is mild and pregnancy does not cause pre- eclampsia to occur then mother and baby seldom have a problem.