Hypertension in pregnancy

In normal pregnancy the arterial pressure falls in the second half of the first trimester: systolic pressure then remains unchanged throughout pregnancy, with diastolic pressure tending to rise gradually towards its prepregnancy level in the later weeks.

Definitions, epidemiology and clinical features—(1) Pregnancy-induced hypertension (PIH), transient hypertension of pregnancy, or gestational hypertension describe new hypertension, defined as blood pressure equal to or in excess of 140/90 mmHg, which without proteinuria affects up to 10% of women after mid term (20 weeks) and resolves after delivery. (2) Pre-eclampsia, which affects 3 to 5% of pregnancies, is defined by the presence of PIH and pregnancy-induced proteinuria arising after 20 weeks gestation that both improve after delivery. Other features include (a) renal insufficiency; (b) hepatocellular dysfunction and/or severe epigastric/right upper quadrant pain; (c) neurological problems—convulsions (eclampsia), severe headaches, persistent scotomata; (d) haematological disturbances—thrombocytopenia, disseminated intravascular coagulation, haemolysis; (e) fetal growth restriction.

Differential diagnosis—the main differential diagnosis of pre-eclampsia is from chronic hypertension, which in its pure form does not share the renal, coagulation, hepatic and placental abnormalities of pre-eclampsia. The perinatal risks of chronic hypertension in pregnancy result from superimposed pre-eclampsia.

Aetiology—the cause of pre-eclampsia is unknown, but it depends upon the placenta and is characterized by diffuse maternal endothelial dysfunction and a systemic inflammatory response.

Management before pregnancy and prevention—women with no more than moderate chronic hypertension should stop antihypertensive treatment before conception. There is no good method of preventing pre-eclampsia, but low-dose aspirin may be effective in some women.

Management during pregnancy—extreme hypertension (≥160/110 mmHg), whatever the underlying cause, is as dangerous as it is in any other medical situation and demands treatment, but there is no clear reason for treating more moderate hypertension on either maternal or fetal grounds, although most centres will initiate treatment at less extreme levels of blood pressure. As far as it is known the progression of moderate pre-eclampsia is not delayed, nor is the later superimposition of pre-eclampsia on moderate chronic hypertension prevented. Key aspects of management include (1) antihypertensive agents—methyldopa is the most thoroughly tested drug for use in pregnancy: no significant adverse reactions have been observed, but because of its side effect profile labetalol and nifedipine are popular alternatives. (2) Magnesium sulphate – this should be given to prevent eclampsia (grand-mal convulsions) in women with the HELLP syndrome (haemolysis, elevated liver enzymes and low platelet counts) and those who have had one eclamptic convulsion. (3) Delivery of the baby and placenta—this is the definitive treatment for pre-eclampsia.