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THURSDAY, Aug. 14, 2003 (HealthDayNews) -- Pregnant women who take aspirin or painkillers known as NSAIDs have a strikingly higher risk of miscarriage, a study finds.
The study of more than 1,000 pregnant women found the risk of miscarriage for those who took aspirin was 60 percent higher than for those who did not and was 80 percent higher for those taking any NSAID (nonsteroidal anti-inflammatory drug) than for those who did not.
No such risk was found for those who used acetaminophen, the active ingredient in Tylenol and the like, say researchers from the Kaiser Foundation Research Institute in California, whose study is published in the Aug. 16 issue of the British Medical Journal.
NSAIDs, widely used to treat arthritis, work by reducing production of molecules called prostaglandins in many organs of the body. Aspirin has the same action. Acetaminophen also inhibits prostaglandin production, but only in the central nervous system.
Animal studies indicate that prostaglandins are needed for implantation in the wall of the uterus, say the researchers, led by Dr. De-Kun Li, a Kaiser Foundation research scientist. Suppressing prostaglandin production "can interrupt the natural process of implantation," Li says.
The researchers interviewed 1,063 women in the San Francisco area who were in the Kaiser Permanente health program and became pregnant between 1996 and 1998, asking about their use of NSAIDs and other painkillers.
There were 149 miscarriages among the 980 women who did not use NSAIDs, a rate of about 15 percent. But 13 of the 53 women who used the drugs miscarried, a rate of 24.5 percent, which means that the risk of miscarriage for users was 80 percent higher, the researchers say. The numbers were similar for those who took aspirin, with a miscarriage rate 60 percent higher for users than for nonusers.
There was a slight, statistically insignificant, increase in the miscarriage rate for women who took acetaminophen.
The risk was highest when NSAIDs were taken around the time of conception or when they were taken for more than a week, the report says.
Li says he hesitates to give advice to women on the basis of the study, because much more work is needed to prove a cause-and effect relationship. But he says that it is sound medical practice for women with chronic conditions that require the use of NSAIDs to consult their doctors about what to do before and during pregnancy, and that other women would do well to use acetaminophen for headaches and other minor pains.
A similar study of more than 30,000 women in 2001 by researchers in Denmark found a comparable increase in miscarriage among NSAID users. As a result, the Royal College of Obstetrics and Gynecology in Britain has issued an advisory telling women to avoid NSAID use during pregnancy.
"It is important to note that the authors of the paper emphasize that they have not shown that these drugs cause miscarriage, only that they are associated with miscarriage," the advisory says, adding that "it would be better if, for the moment, women who knew they were pregnant avoided these drugs, particularly as there are effective alternatives, such as paracetamol [acetaminophen]."
A spokesman for the American College of Obstetrics and Gynecology says the organization has not taken a stand on the issue.
There are about a dozen NSAIDs on the market. Some are over-the-counter, such as ibuprofen (Advil) and naproxen (Aleve). Those that require prescriptions include Celebrex, Voltaren, Lodine, Nalfon, Indocin and Vioxx.