There is no evidence that aspirin therapy during in vitro fertilization (IVF) increases a woman's chances of becoming pregnant, according to an updated systematic review published August 10 in The Cochrane Library.

Aspirin is often prescribed to improve the outcome of women undergoing IVF "despite inconsistent evidence of its efficacy," Charalambos Siristatidis, MD, of the Assisted Reproduction Unit at the University of Athens in Greece, and colleagues note in their review.

They say use of aspirin for this purpose "cannot be recommended due to lack of evidence from the current trial data" and note that "[a]dequately powered trials are needed."

In an interview with Medscape Medical News, Roger Lobo, MD, professor of obstetrics and gynecology at Columbia University in New York City and current president of the American Society of Reproductive Medicine, said it's unlikely such trials would ever be conducted. "There's really no incentive.

"Empirically using aspirin in IVF has been batted around for a long time," Dr. Lobo said. "This meta-analysis combines the existing evidence and confirms that aspirin isn't likely to be of any major benefit in women undergoing IVF." Dr. Lobo did not participate in the Cochrane Review.

More Data; Same Conclusion

Research on the use of aspirin during IVF and other assisted reproduction techniques has yielded mixed results. Some studies suggest that aspirin therapy improves pregnancy rates; others suggest it may increase the risk for miscarriage.

A 2007 Cochrane Review examined data from 9 randomized controlled trials involving a total of 1449 women undergoing IVF or intracytoplasmic sperm injection (ICSI). Participants were treated with low-dose aspirin (≤150 mg once daily) or placebo or no treatment.

The reviewers found that women taking aspirin during IVF or ICSI were not significantly more likely to become pregnant than women in the controls groups. In addition, no significant difference in live birth rates existed between the aspirin and the control groups.

The findings of the updated 2011 Cochrane review mirror those of the 2007 review.

"Based on the available evidence, we reached the same conclusion as the initial version of the review. No single outcome measure demonstrated a benefit with the use of aspirin," the authors report.

The latest review of aspirin therapy with IVF included 13 randomized controlled trials in a total of 2653 women undergoing IVF of ICSI.

The trials compared aspirin (≤150 mg once daily) vs placebo or no treatment, taken either preconceptually or at different stages of the treatment cycle (eg, during down-regulation, during stimulation of ovulation, after egg collection, or after confirmation of pregnancy by a pregnancy test or ultrasonography).

"Aspirin treatment given for varying lengths of time was considered (for example up to different points in the treatment cycle; until confirmation of pregnancy; up to 12 weeks, 34 weeks gestation or delivery)," the authors note.

In the pooled analysis, there was no evidence of an improvement in live birth rate with aspirin (relative risk [RR], 0.91; 95% confidence interval [CI], 0.72 - 1.15) or in the clinical pregnancy rate (RR, 1.03; 95% CI, 0.91 - 1.17).

There was also no evidence of an effect of aspirin on multiple pregnancy rates (RR, 0.74; 95% CI, 0.38 - 1.46), ectopic rates (RR, 1.86; 95% CI, 0.75 - 4.63), and miscarriage rates (RR, 1.10; 95% CI, 0.68 - 1.77), although these findings are based on data from a limited number of studies, the authors note.

Embryo Quality Major Factor in Success

The authors note that one of the largest studies included in the updated review reported on 298 women and showed some benefit in clinical pregnancy rate; 45% of the population using aspirin became pregnant compared with 28% of the control population, yielding a 17% improvement with aspirin.

Nonetheless, they conclude that aspirin for the purpose of improving IVF outcomes cannot be recommended.

Dr. Lobo made the point that "the major factor influencing pregnancy is embryo quality; if you've got a good embryo, aspirin is not going to improve upon that. The theory is that aspirin improves blood flow and the [uterine] lining and so forth, but those aren't major factors in someone with routine infertility," he added.

Despite a lack of evidence of benefit, aspirin is commonly used in women undergoing IVF, Dr. Lobo told Medscape Medical News.

"Many people are grasping at straws, trying everything, so it is used empirically, but this new report pretty much tells us that it is not of value. And there are some downside risks, such as bleeding, even though the doses are low. I think there are more risks than benefits at this point," he concluded.