Pregnant women who take painkillers such as ibuprofen are twice as likely to suffer a miscarriage, a study claims.

Scientists warn that tens of thousands of expectant mothers are taking the pills unaware of the dangers.

A major study has found that women who took ibuprofen or similar painkillers just before they conceived until the 20th week of pregnancy were 2.4 times more at risk.

Although there are clear warnings on the drugs’ packets stating they should not be used in pregnancy, as many as one in six expectant mothers still take them.

The study involved a group of painkillers known as Non-Steroidal Anti Inflammatory Drugs or NSAIDS, which include over-the-counter ibuprofen and naproxen.

Aspirin is also in this category although it wasn’t included in the study, while paracetamol is deemed safe.

The researchers believe taking any number of the drugs can lead to the embryo not being properly implanted in the womb meaning a woman is far more likely to suffer miscarriage – also known as a spontaneous abortion.

Around one in eight pregnancies end in miscarriage and the majority happen in the first 12 weeks.

Often there is no obvious cause but older women and those who smoke, drink heavily or are obese are at far higher risk.

The study published in the Canadian Medical Association Journal involved 47,050 women aged 15 to 45.

They were asked whether they had taken the painkillers at any time in the first 20 weeks of their pregnancy – or two weeks before they became pregnant.

Despite the warnings some 17 per cent had taken the drugs – nearly one in six.

Dr Anick Bérard of the University of Montreal said: ‘We consistently saw that the risk of having a spontaneous abortion was associated with gestational use of diclofenac, naproxen, celecoxib, ibuprofen and rofecoxib alone or in combination.

‘Women who were exposed to any type and dosage of non-aspirin NSAID during early pregnancy were more likely to have a spontaneous abortion.’

But doctors pointed out the risks of a woman suffering a miscarriage due to painkillers were very small.

They also said the study did not take into account other possible causes such as smoking and obesity.

Dr Virginia Beckett, spokesman for the Royal College of Obstetricians and Gynaecologists, said: ‘It is important that any woman before conception and during pregnancy plans their pregnancy and reduces their risk of any complications through maintaining a healthy lifestyle.

‘It is safe to take paracetamol during pregnancy.’