Women undergoing in-vitro fertilization (IVF) are often told that a daily aspirin will help boost the odds of success. But a new research review found no evidence the tactic works.
Combining the results of 13 international studies, researchers found that a low daily dose of aspirin had no clear effect on IVF pregnancy or birth rates.
Three of the studies looked at birth rates. Of 525 women who used aspirin during their IVF treatment cycle, 108 gave birth.
But the odds of success were similar among women not given aspirin: of those 528 women, 119 gave birth.
"Couples undergoing IVF often feel so desperate that they are prepared to try anything that may improve their chances of conceiving," said lead researcher Dr. Charalambos Siristatidis, of the University of Athens in Greece, in a written statement.
"But given the current evidence," he said, "there is still no basis to recommend that women take aspirin to help them become pregnant."
The researchers reported their findings in the Cochrane Library, which is published by the Cochrane Collaboration, an international research organization that evaluates medical evidence.
In theory, aspirin could improve IVF success by boosting blood flow to the ovaries and uterus. It might also help by preventing blood clots in the vessels of the placenta, which helps nourish the baby before it's born. But studies have come to mixed conclusions.
There is a small minority of women who have repeat miscarriages because of problems with blood clotting, said Dr. Roger Lobo, a professor of obstetrics and gynecology at Columbia University in New York who was not involved in the review.
If a woman undergoing IVF has blood-clotting issues, then aspirin or other blood-thinners may help, said Lobo, who is also president of the American Society of Reproductive Medicine.
But for most women having IVF, he told Reuters Health, "it's really the embryo quality that's the major factor. So I'm not surprised that aspirin shows no benefit overall."
The studies in the review included a total of 2,653 women undergoing IVF. The trials were randomized, meaning roughly half the women were randomly assigned to take 80 to 100 milligrams of aspirin per day, and the other half were assigned to a no-aspirin "control" group. Randomized controlled trials are considered the most reliable type of study.
In most studies, women started taking aspirin at the beginning of the IVF process. The duration of the treatment varied from study to study.
One of the larger studies that looked only at pregnancy rates did suggest a benefit, the researchers note. Of 300 women, the pregnancy rate among aspirin users was 45 percent, versus 28 percent of women not on aspirin.
But when the researchers combined the results of different studies, they found no overall effect on women's pregnancy or birth rates, or on their risk of miscarriage.
Like Siristatidis, Lobo too noted that many couples undergoing infertility treatment are desperate to try anything that could raise their chances of having a baby, even in theory. But he stressed that even low-dose aspirin can have risks, including gastrointestinal bleeding.
"Based on the evidence, there really appears to be no benefit from using aspirin," Lobo said. "And if you add to that the fact that there are risks, it probably shouldn't be done."