A daily low dose of aspirin does not appear to prevent subsequent pregnancy loss among women with a history of one or two prior pregnancy losses, according to researchers at the National Institutes of Health.
However, in a smaller group of women who had experienced a single recent pregnancy loss, aspirin increased the likelihood of becoming pregnant and having a live birth.
Many health care providers prescribe low dose aspirin therapy for women who have had a pregnancy loss (miscarriage or stillbirth), and who would like to get pregnant again. However, the effectiveness of this treatment has not been proven, the researchers wrote.
In the largest study of its kind, the researchers randomly assigned more than 1,000 women with a history of pregnancy loss to either daily low dose aspirin or a placebo. The women began taking the equivalent of one low dose aspirin (81 milligrams) each day while trying to conceive. The researchers reported that, overall, there was no difference in pregnancy loss rates between the two groups.
"Our results indicate that aspirin is not effective for reducing the chances of pregnancy loss in most cases," said first author Enrique Schisterman, Ph.D., Chief of the Epidemiology Branch at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the institute that led the study.
Dr. Schisterman, added, however, that additional research was needed to investigate the finding that women who had experienced a single, recent pregnancy loss (before 4 1/2 months of pregnancy and within the past year) had an increased rate of pregnancy and live birth while on aspirin therapy.
Among this group, 78 percent of those who took aspirin became pregnant, compared with 66 percent of those who took the placebo. For this subset of women, 62 percent of the aspirin group and 53 percent of the placebo group gave birth.
The study authors hypothesized that aspirin therapy might increase the conception rate by increasing blood flow to the uterus. The researchers called for additional research to determine if aspirin therapy might be helpful for improving fertility in other subgroups as well, such as women who can't establish a pregnancy because the embryo fails to implant in the uterus.
Dr. Schisterman collaborated with colleagues at the NICHD and the University of Utah Health Sciences Center, Salt Lake City, Utah; the University of Haifa, Israel; the University at Buffalo, New York; The Commonwealth Medical College, Scranton, Penn; and the University of Colorado, Denver, Colo.
The findings appear in The Lancet.
The researchers referred to their study as the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial. The study took place at four university medical centers over a five-year period. Women participating in the trial were between 18 and 40 years of age and predominantly white. Participants took a daily dose of either aspirin and folic acid (http://www.cdc.gov/ncbddd/folicacid/recommendations.html) or placebo and folic acid. Folic acid is recommended for all women of child bearing age, because it reduces the risk for neural tube defects, a class of birth defects that can affect the brain and spine.
Women were followed for up to six menstrual cycles while they were trying to become pregnant and through pregnancy if they became pregnant. Aspirin was stopped at 36 weeks (about eight months) of gestation.
For the total number of women in the study, 13 percent of women who took aspirin and became pregnant subsequently experienced another loss, compared with 12 percent who took the placebo. Ultimately, 58 percent of women taking aspirin and 53 percent of the placebo group got pregnant and later gave birth.