When Jean McLaurin had a miscarriage she was prepared for some discomfort and bleeding in the days after the routine operation to remove the products of conception. A week later, however, the bleeding was so heavy that Mrs McLaurin, 36, thought something must be wrong. Her doctor diagnosed a post-operative infection and prescribed antibiotics.

'It seemed to work at first,' says Mrs McLaurin, but the bleeding became heavy again. After a month her doctor prescribed more antibiotics. Her stomach was also distended. Three days later she was convinced she was haemorrhaging. 'I telephoned the doctor who told me not to worry, but by this time I was so distressed I went to the emergency unit at the hospital, which admitted me straight away.'

The following day she was given a second 'ERPC' operation to evacuate the retained products of conception, and the bleeding stopped. Mrs McLaurin assumed that the first operation had not completely cleared out her womb, as she knew this sometimes happens, leaving remains of the pregnancy to irritate the uterine lining and cause bleeding. It had been an uncomfortable experience.

Six weeks later she was surprised to receive a telephone call from the hospital asking her to go in to discuss the results of tests on the tissue from the second operation. At that meeting Mrs McLaurin was told that she had had a partial hydatidiform mole.

Complete and partial molar pregnancies occur in about one in every 1,000 births. A mole is an abnormal placenta that develops into a tumour because the woman's egg is genetically haywire from the moment of conception. The tumour is usually benign.

News about the mole came as a shock to Mrs McLaurin, not least because she had never heard of such a thing. She had also feared that she might have become pregnant again since her first operation. Molar pregnancies can cause morning sickness. Home pregnancy tests had showed positive, leaving her not knowing whether she had started a normal pregnancy or if there was an abnormality and that she faced another miscarriage.

'My mole was not diagnosed until two months after the original ERPC,' she says. 'I want to know why it took so long. I think doctors should give clearer advice to women after miscarriages to let them know what sort of after-effects are normal and which are abnormal. They shouldn't automatically assume that everything is all right, especially when, with moles, there can be such horrible complications if treatment is delayed.'

Little information is available to women about the risk of hydatidiform moles. Few pregnancy handbooks mention them and they are not included in the information sheets given to women who have suffered miscarriages. Yet their incidence makes them as common as more frequently discussed abnormalities such as Down's syndrome.

Moles occur when the egg is fertilised by the sperm. With a complete mole, no foetus forms but the pregnancy can appear to develop normally because chorionic gonadotrophin, the pregnancy hormone, is present.

The uterus expands to contain the placenta, which, instead of nourishing the foetus, grows as a mass of rapidly multiplying cysts. With a partial mole there is evidence of a foetus forming alongside the cysts, although it cannot usually survive. There are reports that traces of hair and even teeth have been found in the tumours.

Professor Edward Newlands, a medical oncologist and clinical director of the mole follow-up centre at Charing Cross Hospital, London, has wide experience of molar pregnancies. 'For reasons that are still not understood, the egg deletes all the mother's genes and carries only the paternal genes,' he says.

But the real cause of hydatidiform moles is not known. 'There is a maternal age factor which indicates that moles are connected with the ovum's efficiency,' he says.

Records kept for 20 years by Charing Cross and two other mole treatment centres, in Dundee and Sheffield, show more molar pregnancies in the under-16s and among women in their forties and fifties. There are also ethnic variations. 'There are groups around the Pacific Basin, including the Japanese, Koreans and Indonesians, which have twice the incidence of moles compared with Caucasians,' says Professor Newlands.

Moles can be cancerous. In about 10 per cent of cases the mole continues to grow in the uterus after an evacuation operation and the disease - choriocarcinoma - can spread to other parts of the body, usually the lungs and the brain. Careful monitoring in the form of regular blood and urine tests is needed to be sure that the mole dies out completely in the womb. Pregnancy must be avoided for at least six months if the mole has been successfully removed, or for a year after treatment if chemotherapy is needed to be certain that the mole has been destroyed.

Caught early, choriocarcinoma is almost always curable. At the Charing Cross centre, records show a 94 per cent survival rate after 15 years. Deaths occur only if there has been a delay in diagnosis, allowing the disease to spread, or if there is resistance to chemotherapy.

Rob Smith, a consultant obstetrician and clinical director of the Scottish mole follow-up centre at Ninewells Hospital, Dundee, says there has been one terminal case in Scotland in the past 10 years. 'Most cancers have the genetic make-up from the afflicted person. This is unlike others because it carries only the partner's genes and that could be what makes it easier to treat,' he says.

Choriocarcinoma can occur after any normal pregnancy or miscarriage but it is found in only about one in 45,000 births. The symptoms can be irregular bleeding or chest problems and may not show themselves for years.

'One lady suffered a molar pregnancy in 1985 and had twins in 1989, after which choriocarcinoma was diagnosed,' says Professor Newlands. 'We were able to show that the cancer was genetically linked to her first pregnancy.'

More could be done. One problem is that the results of ERPCs after miscarriage are not routinely analysed.

'I have a biased view that if something goes wrong in pregnancy you never know why unless you analyse,' says Professor Newlands. 'I think that to subject a woman to an ERPC without analysis is wrong.'

(Photograph omitted)