Women who take any amount of ibuprofen in early pregnancy could have more than double the risk of miscarriage, new research suggests.
A class of painkillers known as non-steroidal anti-inflammatory drugs increase the risk of miscarriage in the first 20 weeks of pregnancy, experts said.
Previous studies have shown inconsistent results when examining the effect of NSAIDs on pregnancy.
The new study, published in the Canadian Medical Association Journal , examined a number of commonly-used NSAIDs including ibuprofen, naproxen and diclofenac.
The research found that women who took any type, and any dose, of NSAID had a 2.4 times higher risk of miscarriage than those who did not use any.
Overall, 4,705 cases of miscarriage were analysed, of which 352 (7.5 per cent) involved women taking NSAIDs.
Women in the entire sample were aged 15 to 45, and they were compared with women of a similar age who did not suffer a miscarriage (of which 2.6 per cent had been exposed to NSAIDs).
The highest risk was for diclofenac when used alone, while the lowest was for a drug called rofecoxib, which was withdrawn in 2004 over safety concerns.
Anick Berard, from the University of Montreal, who worked on the study, said: “The use of non-aspirin NSAIDs during early pregnancy is associated with statistically significant risk (2.4-fold increase) of having a spontaneous abortion.
“We consistently saw that the risk of having a spontaneous abortion was associated with gestational use of diclofenac, naproxen, celecoxib, ibupro-fen and rofecoxib alone or in combination, suggesting a class effect.”
The authors concluded: “Women who were exposed to any type and dosage of non-aspirin NSAID during early pregnancy were more likely to have a spontaneous abortion.
“Given that the use of non-aspirin NSAIDs during early pregnancy has been shown to increase the risk of major congenital malformations and that our results suggest a class effect on the risk of clinically detected spontaneous abortion, non-aspirin NSAIDs should be used with caution during pregnancy.”
Janet Fyle, professional policy adviser at the Royal College of Midwives (RCM), said: “We need to advise women, as midwives often do, to avoid buying over the counter medication for pain relief.
“If a pregnant woman does need to take any analgesia, then paracetamol would be appropriate.
“This would be after assessment by the midwife/or GP as to the nature of the pain.
“The most important advice to pregnant women is to report any pain to the midwife and avoid buying over the counter medication, as it may be contraindicated in pregnancy.”
Earlier this year, a study found taking NSAIDs daily carried a small increased risk of heart attack and stroke.
The drugs are sometimes prescribed long-term to treat painful conditions such as arthritis.
Other studies have suggested they can cut the risk of breast cancer and could help fight bowel cancer.