Pre-eclampsia is an illness arising only in pregnancy which can affect the mother, her unborn child, or most commonly, both. It can occur at any time from around twenty weeks to as late as several days after delivery. In the mother, the condition causes a number of symptomless disturbances – including raised blood pressure (hypertension) and leakage of protein in the urine (proteinuria) – which can progress to serious illness if undetected. The unborn baby may grow more slowly than normal or suffer potentially dangerous oxygen deficiency.

In its broadest form and including gestational hypertension, pre-eclampsia affects as many as one in 10 of all pregnancies, making it the most common of the serious antenatal complications. It occurs more often in first pregnancies, although a minority of women who have suffered it once get it again in one or more subsequent pregnancies. Pre-eclampsia is usually mild, but 1-2 in every 100 first pregnancies is so severely affected that there is a serious risk to the life of the baby – and even the mother. Every year in the UK about 1000 babies die because of pre-eclampsia – many of these as a consequence of premature delivery rather than the disease itself. Some 7 mothers die each year from complications of pre-eclampsia in the UK.

No one can predict with certainty who will get pre-eclampsia. Every woman is at risk in her first pregnancy, although the risk is greater for those with a strong family history of the complication. Women who have had pre-eclampsia in a first pregnancy may get it again. However, those who have enjoyed normal first pregnancies rarely get pre-eclampsia in subsequent pregnancies. The risk of repeat attacks is increased if the mother is carrying twins or has one of several chronic medical problems, including high blood pressure, kidney disease, diabetes or, to a lesser extent, migraine. Mothers over 40, or with a gap of 10 years since their last baby may also be at risk. Women with a body mass index over 35 or weight of 100kg or more may also be of higher risk.

No one knows for sure, although genetic factors are probably involved, since women whose mothers and sisters have suffered pre-eclampsia are more likely to get it themselves. What is known is that pre-eclampsia originates in the placenta – the special pregnancy organ which links a mother to her unborn child. The placenta needs a large and efficient blood supply from the mother to sustain the growing baby. In pre-eclampsia, the placenta runs short of blood either because its demands are unusually high – as with twins – or because the arteries in the womb did not enlarge as they should have done when the placenta was being formed in the first half of pregnancy. This shortage of blood has potentially serious consequences for mother and baby.

Signals from the deficient placenta affect the mother’s blood vessels, raising her blood pressure and disturbing her kidney function, so that waste products which should be excreted in the urine accumulate in the blood, while valuable blood proteins leak into the urine. As the disease progresses, the mother’s liver, lungs, brain and blood clotting system can also be affected. Eclampsia (convulsions), cerebral haemorrhage (stroke), pulmonary oedema (fluid in the lungs), kidney failure, liver damage, and breakdown of the blood clotting system (disseminated intravascular coagulation) are the most dangerous complications – all of them fortunately, very rare.

Pre-eclampsia has no symptoms in its early stages, when it can be detected only in routine screening tests carried out in antenatal clinics. A combination of rising blood pressure and protein in the urine suggests pre-eclampsia, although there is no foolproof diagnostic test. Swelling (oedema) of the hands, feet and face caused by fluid retention is often a feature of pre-eclampsia, but is also common in normal pregnancy. Symptoms like upper abdominal pain, vomiting, severe headache, and visual disturbances (such as ‘flashing lights’) sometimes arise when the disease has reached an advanced stage. These symptoms should therefore never be ignored in pregnancy although, since each can have other causes, they do not necessarily signal danger.

A pregnancy complicated by pre-eclampsia cannot be restored to normal. But the disease itself is ended when the baby is born and with it the placenta which is the seat of the problem. This is usually in the best interests of both mother and baby. But dilemmas arise when early delivery would solve the mother’s problems but put the baby at risk of the effects of extreme prematurity.

Mothers are admitted to hospital if they have  pre-eclampsia – which means protein in the urine as well as high blood pressure. This is to enable doctors and midwives to monitor the progress of mother and baby as closely as possible so that a safe induction, if necessary carried out before complications set in. Pre-eclampsia is progressive – it doesn’t get better and usually gets worse. So, once admitted, mothers are not normally allowed home until after their baby has been born. Antihypertensive drugs, which reduce high blood pressure, are often prescribed; although they do not affect the underlying disease, they can reduce the risk of some complications, such as cerebral haemorrhage. Anticonvulsant drugs may also be prescribed to ward off eclamptic fits.

As the blood supply from the mother to the placenta is restricted, the baby’s supply of nutrients and oxygen may be reduced, leading at first to slower than normal growth (intrauterine growth retardation – IUGR) and later to oxygen starvation. Once pre-eclampsia is suspected or known, the unborn baby is monitored as closely as the mother so that the delivery can be carried out before its problems become serious. Decisions about early induction are particularly difficult when a premature foetus (of under 28-30 weeks’ gestation) is severely affected by pre-eclampsia but could not be certain of survival outside the womb.

For the great majority of mothers,  the birth of her baby reverses all the effects of pre-eclampsia, although recovery may be preceded by a final crisis. For an unfortunate few, however, some organ damage remains after the disease itself is cured. It is not uncommon for women who have suffered pre-eclampsia in one or more pregnancies to develop chronic high blood pressure later on in life. But this is thought to reflect an inbuilt tendency to blood pressure problems rather than a history of pre-eclampsia. There are no known health problems for babies and children who have been affected by pre-eclampsia unless they suffered extreme starvation of oxygen in the womb or had to be delivered very prematurely.

Women who have suffered pre-eclampsia in a first pregnancy should be monitored more closely and more frequently than usual in subsequent pregnancies, since there is a risk that the condition will recur, although usually in a milder form. Nevertheless, most mothers who have suffered even the most severe form of the disease in a first pregnancy enjoy perfectly normal subsequent pregnancies.

There is no hard evidence that pre-eclampsia can be prevented by what you eat, whether you smoke or drink, how hard you work or how much rest you take. However, there is some evidence that small daily doses of aspirin, taken under medical supervision, may be able to prevent or delay the onset of the disease in some high-risk mothers. This is because aspirin works directly on specialised blood cells known as platelets, which help with clotting and are involved in the disease process.

Your best plan is to co-operate fully with the system of antenatal checks, which is designed to detect the earliest signs of pre-eclampsia. If possible, have yourself referred to a consultant who takes a special interest in pre-eclampsia, and see him or her early in your pregnancy – or even before conception – to plan your antenatal care programme.

Take an active interest in your antenatal checks; never miss an appointment; make sure you are monitored more frequently if your blood pressure is raised, and admitted to hospital if protein appears in your urine (only one or more ‘plusses’ (+) in a urine test is important: ‘trace amounts’ can be ignored.) Always report any worrying signs or symptoms to your doctor and do not allow him or her to dismiss you without first checking your blood pressure and urine.