A 29-year-old solicitor's wife from the Home Counties did everything right during her first pregnancy. She avoided cigarettes and alcohol, ate a sensible, varied diet and had plenty of rest. She swam regularly and went to yoga antenatal classes.

Yet as she recovered in a postnatal ward, her newborn daughter struggled for survival in a premature baby incubator down the corridor. This 'skin-and-bones mite', as she was described by doctors, had to be delivered by Caesarean at 34 weeks. She weighed less than a bag of sugar and had serious breathing problems.

Why would this middle-class English woman from a comfortable home, well nourished and well informed about antenatal care, give birth to a baby who looked like a Third World starveling suffering from the kind of oxygen deprivation normally found in high mountain regions? The answer is pre-eclampsia, also known as pre-eclamptic toxaemia (PET), the mysterious 'high blood pressure disease' of pregnancy. According to Dr Christopher Redman, a leading researcher into PET, it affects at least one in 10 expectant mothers. It also leads to the deaths of 15 women a year in the UK and kills up to 1,000 babies annually, usually through a combination of damage in the womb and premature delivery.

Dr Redman, who is head of the High-Risk Baby Unit at the John Radcliffe Hospital, Oxford, says: 'Two or three babies die as a result of it in Britain each day. This is a young baby totally deprived of life - and a bitter tragedy for a young family trying to get themselves started.'

He and other specialists now believe that the problem may begin very early in pregnancy when the mother's faulty immune system tries to reject the developing foetus. Instead of a miscarriage occurring, the pregnancy continues and with it the risk of damage to the baby.

Full-blown eclampsia, signalled by rapidly soaring blood pressure, fits, kidney, liver and blood damage, brain haemorrhage and sometimes coma, remains one of the chief causes of maternal death in the Western world.

Dr Redman's unit regularly treats infants weighing less than 2lb 'who look as if they have come straight from a famine in Ethiopia'. Some are so small and damaged by progressive starvation and shortage of oxygen before birth that they do not stand a chance. Others survive but are handicapped. The lucky ones are those who are merely underweight.

Yet 30 years of research have failed to reduce PET's impact. Some research has suggested that low-dose aspirin taken during pregnancy might prevent it, and the results of a world-wide Medical Research Council trial of aspirin in early pregnancy will be published this autumn. Dr Redman, however, warns against self-medication until possible side effects are known - aspirin can cause both mother and baby to bleed.

One of the problems of diagnosis is the condition's extreme unpredictability. Symptoms include swelling, headaches, dizziness and flashing lights - all of which can be side effects of normal pregnancy. Sometimes a woman has no symptoms at all. Antenatal tests, however, show up the three generally accepted clinical signs: a sudden, sustained increase in blood pressure, generalised swelling, and protein in the urine. PET develops quickly, blowing up to life-threatening proportions in 10 to 12 days. Hence the importance of not skipping antenatal appointments, says Dr Redman.

The disease is no respecter of class or income, although certain types of pregnant women seem to be more prone than others. The vulnerable group includes women of more than 35, those undergoing a first or multiple pregnancy and those with a family history of PET or a medical condition such as kidney disease or high blood pressure. A woman who has PET in her first pregnancy has a one in 20 chance of a repetition.

Senior midwives at one London teaching hospital also believe there is a new type of PET sufferer: the high-achieving career woman in her late thirties, expecting her first baby, working in a stressful job until the last moment and psychologically loath to allow her pregnancy to control her life.

'Nobody knows its cause,' says Dr Redman. 'That's why we're walking on sand, trying to find a successful treatment.'

So far, doctors have prescribed bed rest, drugs to lower blood pressure and sedatives to calm the mother. Some women have been put on special diets or told to reduce their salt intake. Others have been advised to give up work early. But the only sure solution remains delivery. If the condition becomes life-threatening, birth will be induced or a Caesarean performed. Even then, some women can develop PET during labour or even just after their baby's birth, which can still be dangerous for the mother.

Dr Redman thinks that in PET the process of establishing the placenta is somehow sabotaged, giving rise to the baby's eventual starvation of food and oxygen. In normal pregnancy, arteries in the womb wall change. They need to soften and stretch enough to keep a pint of blood circulating around the baby each minute, but in PET sufferers they stay tough and narrow. These arteries are never directly linked to the baby but the failure of the network to develop properly means the baby is plugged into a faulty system from the start. In the second half of pregnancy, fat and blood waste deposits clog the arteries and chunks of placenta may die.

Mother and baby both adapt - her blood pressure rises, the baby concentrates its growth on its brain rather than its body - but nothing can reverse the damage and there comes a point when the baby is better out than in.

No test has yet been developed that can detect these early roots of PET. The Radcliffe team is isolating and studying particular cells associated with pregnancy, including those that are part of the immune system. It will be a long business, as the womb lining contains about 10 different types of cell, each of which has six or seven chemical messengers; and studying just one is a year's work.

'Pre-eclampsia: The Facts', by Christopher Redman and Isabel Walker, is published by OUP; pounds 8.99 (pbk). A charity, Action on Pre-eclampsia, will be launched in November. Details from APEC, 61 Greenways, Abbots Langley, Herts, WD5 0EU.

(Photograph omitted)