NEW ORLEANS – Maternal body mass index does not affect the efficacy of low-dose aspirin for preventing preeclampsia or preterm birth, according to a secondary analysis of data from the National Institute of Child Health and Human Development’s Maternal-Fetal Medicine Units Network trial.
In the large randomized controlled trial, aspirin was not found to be of benefit for preventing preeclampsia; however, some meta-analyses have suggested a modest benefit, Dr. Jessica Cantu noted at the annual meeting of the American College of Obstetricians and Gynecologists. In one meta-analysis of individual patient data from 31 studies that included more than 32,000 women, aspirin-treated patients had a 10% relative risk reduction, compared with controls, she said.
In fact, aspirin is the only intervention that has shown any potential benefit for preventing preeclampsia, which occurs in 5%-8% of pregnancies and causes 18% of maternal deaths, said Dr. Cantu of the University of Alabama at Birmingham.
"So why is it that the randomized controlled trials have not shown benefit? Potential reasons are that the aspirin dose used was small in these trials, ranging from 50 to 150 mg/day. Second, the contradictory results may lie in the timing of initiation, with more recent data suggesting benefit when aspirin is initiated at less than 16 weeks’ gestation. Finally, maternal obesity is a potential reason for the lack of significant benefit in clinical trials," she said.
Since obese women are at increased risk for preeclampsia, and since obesity and preeclampsia share certain pathophysiological features, including endothelial dysfunction, oxidative stress, and an increased state of inflammation, it seems plausible that obese pregnant women might benefit the most from low-dose aspirin therapy.
"On the other hand, study dose of low-dose aspirin may be too small to have an effect on these women," she said.
To take a closer look at the impact of body mass index on outcomes in the Maternal-Fetal Medicine Units Network trial, which included women at high risk for preeclampsia, a secondary analysis of data from 2,479 women in that trial was performed to determine if outcomes varied by BMI class.
No significant differences were seen in the relative risk of preeclampsia between those with a BMI of 30 or less and those with a BMI of greater than 30 when aspirin was initiated at 13-26 weeks’ gestation. There also was no difference between the groups with respect to the rate of delivery prior to 37 weeks’ gestation.
Even after additional analyses were performed to compare outcomes in obese and nonobese patients from each of four high-risk subgroups of patients in the study, and when patients were further stratified into four BMI subgroups (normal, overweight, obese, and morbidly obese) the effects of aspirin therapy did not differ based on BMI class.
This study is limited by the fact that it involves a secondary analysis of data. Also, the timing of initiation of aspirin therapy may have contributed to the overall lack of an effect, Dr. Cantu said.
"These limitations notwithstanding, we conclude that there is no effect of maternal BMI on aspirin efficacy for the prevention of preeclampsia or preterm birth," she said.
Dr. Cantu reported having no disclosures.