REUTERS: Women who use certain over-the-counter painkillers such as aspirin early in pregnancy may not have an increased risk of miscarriage, according to a U.S. study.

Researchers writing in the journal Obstetrics & Gynecology looked at the possible connection between miscarriage and non-steroidal anti-inflammatory drugs (NSAIDs), which include common painkillers like aspirin, ibuprofen and naproxen.

Some studies have hinted at an increased miscarriage risk among women who use NSAIDs around the time they conceive or in early pregnancy, but other studies have failed to find a connection.

"Our findings suggest that use of nonprescription over-the-counter NSAIDs in early pregnancy does not put women at increased risk of spontaneous abortion," wrote study leader Digna Velez Edwards from Vanderbilt University in Nashville.

Much of the evidence suggesting a risk has been based on prescription NSAIDs, Edwards said, but most women of childbearing age use over-the-counter NSAIDs for occasional aches and pains.

So Edwards and her colleagues looked at use of the over-the-counter drugs among nearly 3,000 pregnant women who were part of a larger study.

Overall, 43 percent said they'd used the painkillers at some point around the time they conceived or in their first six weeks of pregnancy.

Thirteen percent of all women suffered a miscarriage during the study, but the risk was no greater for women who'd used NSAIDs regardless of the number of days they took the drugs, the researchers found.

On the other hand, Edwards said, "we can never know whether NSAIDs or any other medication are completely safe for pregnant women."

Ethically, researchers can't do clinical trials where they randomly assign pregnant women to take a medication or not. Instead, they have to rely on studies like this one, which have limitations such as relying on women's memories and ability to accurately report their NSAID use.

There are biological reasons to believe that NSAIDs could pose a miscarriage risk, Edwards added.

The drugs affect hormone-like substances called prostaglandins - and it's possible they could interfere with the normal prostaglandin changes that happen early in pregnancy. But nobody really knows for sure.

In general, experts recommend that women limit their medication use during pregnancy, if possible. It's thought that acetaminophen is the safest option for occasional pain relief during pregnancy.

The study was partly funded by the National Institutes of Health.