We arranged to meet at Pizza Express, as child-friendly as London N1 could manage in the late 90s, and good territory for my 14-month-old son. I would be in France the day my friend's baby was due and I wanted to wish her well.

But Judith did not look right. She was gaunt and scratched constantly, tearing at her wrists and the palms of her hands. Joseph, my son, had severe eczema as a baby and I recognised the same self-absorbed action. She ate very little, toying with her food.

Judith's GP had diagnosed the itching as "just another symptom of late pregnancy" - like eating coal - and had prescribed a moisturiser and mild steroid cream, but to no effect. Judith was desperate for sleep; the itching was worse at night and she spent hours pacing the house, scratching.

When James was born, eight days after his due date, it was a normal birth until Judith haemorrhaged. As the delivery team at University College Hospital went into overdrive, she lost two litres of blood. Tests revealed that she had obstetric cholestasis (OC), a liver condition in pregnancy that can kill babies.

That was four years ago. In 2000, the Guardian was one of the first national newspapers to highlight the danger signs of OC. Severe itching of hands, feet and limbs in the third trimester is one of the key indicators, as well as unusually dark urine. But babies are still dying from it, so what is going wrong?

Normally, bile is produced in the liver and flows down to the intestines, where it helps with digestion. In pregnant women with OC, the flow of bile reduces, leading to a dangerous build-up of bile salts in the mother's blood, resulting in foetal distress and, in some cases, premature birth or stillbirth. Recent evidence suggests that the abnormal level of bile salts may affect the unborn baby's heart, causing death. Post-partum haemorrhage is also common. If OC is suspected, a routine liver function test can confirm the condition - sufferers show raised levels of certain enzymes. But a serum bile acid test can also confirm OC before enzyme levels start to accelerate.

Jenny Chambers, 44, lost two babies through OC. Her efforts to make sure "it never happened again to anyone else" led her to set up the Obstetric Cholestasis Support Group in 1991. Her helpline answer service asks women to state how many weeks pregnant they are so that calls can be prioritised. The condition is time-critical: at present, all doctors can do is monitor the mothers and deliver babies early - no later than 36 to 37 weeks. Vitamin K can also be given to affected women to reduce the risk of haemorrhage.

Chambers hopes to make the symptoms of OC common knowledge, but does not wish to create panic. "Not all babies have a problem with cholestasis - they will go to term and be delivered safely and well, but it is the small number who won't be fine - they are the babies we are trying to protect," she explains.

Drug therapy is helping some women, but the priority is to establish what causes the condition. Medical teams in Birmingham and London are looking at the possibility of gene mutation affecting the transportation of bile. Evidence suggests that it may be triggered by a genetic susceptibility, with other non-genetic factors - diet, for example - modulating its severity. Researchers believe that the condition is inherited and are keen to trace a generational link. "Ideally, they hope to be in a position to pre-test for OC susceptibility even before pregnancy, although it's not yet clear whether the mother or father carries the gene," says Chambers.

It is estimated that up to one in 200 women in the UK may be affected. A government inquiry into perinatal mortality in 1996 revealed that 5% of unexplained stillbirths were probably related to OC.

When Judith was expecting her second son, Alexander, now a robust 14 weeks old, the systems were in place. Throughout the pregnancy her bile acid levels were monitored. (Having previously had OC does not guarantee you will get it again but the chances are significantly higher - the condition recurs in 80-90% of pregnancies.) At 33 weeks, when the itching started, she was given anaesthetic cream to calm her skin and a timetable to calm her nerves. Doctors have to strike a balance between leaving the baby as long-term as possible and delivering before the liver dysfunction starts to destruct. Alexander was induced at 37 weeks, a healthy 7lb 5oz baby.

The support structure was there but Judith is angry that she still had to fight for information. "What happens to people who don't query the medics, aren't as persistent or don't have easy access to sources of information?'

Weeks before the birth of Alexander, another mother lost her baby. She had all the symptoms, told the doctors that she thought she had OC and they carried out liver function tests, which proved positive. The consultant decided not to act; the baby was stillborn.

Chambers understands the pain of losing a child but she has some sympathy with obstetricians. "The problem is that you don't get clear signs of the baby going into distress. When a baby does get into difficulty and dies, it is sudden. No amount of testing can stop that from happening."

Judith realises she was one of the lucky ones. "It shouldn't still be happening," she says. "It shouldn't happen to any mother."

· The Obstetric Cholestasis Support and Information Line tel: 0121 353 0699. Email: JennyChambersOC@aol.com