Researchers say that women who have IVF treatment are more likely to suffer a potentially life-threatening condition than those who conceive naturally.

They say the risk of developing placenta praevia, a condition in which the placenta covers the cervix, was six times higher in women carrying one child conceived through assisted reproduction.

A team of researchers from the department of obstetrics and gynaecology at St. Olavs University Hospital in Trondheim, Norway say that mothers who have more than one baby, conceived both naturally and through IVF, were three times more likely to develop the condition than women who conceived naturally.

The researchers calculated the risk rose from about three in 1,000 pregnancies in the general population, to 16 in 1,000 for women who had had IVF.

Placenta praevia which is also known as low-lying placenta, occurs when the placenta remains near the opening of the cervix and blocks the baby’s passage into the birth canal.

The condition is serious and can lead to fatal bleeding and to the loss of the baby.

Nothing can be done to alter the position of the placenta once this has happened and delivery is carried out by caesarean section.

Dr. Liv Bente Romundstad, who led the team, says it remains unclear why pregnant women who have IVF have an increased risk of developing placenta praevia but she suspects one cause could be the position in which the embryo is placed in the uterus when it is transferred through the cervix.

That very procedure she says could induce uterine contractions due to the release of prostaglandins [hormone-like substances] after stimulation of the cervix, resulting in more embryos implanting low-down in the uterus.

The research which was based on 845,300 pregnancies between 1988 and 2002, is thought to be the largest study into the link between placenta praevia and IVF.

Fertility specialists usually implant fertilised embryos 2cm from the top of the uterus in order to avoid an ectopic pregnancy.

The Human Fertilisation and Embryology Authority said the research would be carefully considered by its Scientific and Clinical Advances.

The study is published in the journal Human Reproduction.