We thank Drs O’Callaghan and MacLennan and their coworkers for their interest in our article.

We appreciate that Drs O’Callaghan and MacLennan attempted to replicate our findings. Differing results may be due to the fact that their sample includes infants of all gestational ages and does not provide separate analyses for the subsample of infants who were born at <28 weeks of gestation.

We also thank Drs Demmers and Bujold and Ms Roberge for their interest in our article and regret that they were not pleased with our findings and conclusions. They suggested that we could “mislead both women and healthcare providers…thereby compromising the appropriate use of a treatment that can prevent serious maternal and neonatal morbidities.” However, our study did not examine the effect of low-dose aspirin and the subsequent risk of preeclampsia or intrauterine growth restriction. In our study, only 2% of pregnant women with severe preeclampsia reported aspirin consumption; we have no knowledge of the women who took aspirin and did not deliver at <28 weeks of gestation. Thus, our findings cannot speak to the efficacy of low-dose aspirin in the prevention of severe preeclampsia and therefore should not be viewed as calling into question reports of the benefits of aspirin prophylaxis.

We agree with their comment that women who deliver at <28 weeks of gestation generally have the worst perinatal outcomes; however, our entire sample fell into this category, and, as such, this would not have biased our conclusions. We also agree that not having information about the dosage and timing of medication use is a limitation of our study; we mentioned this point in the limitations section of our article: “…perhaps equally important is our not having assessed the timing, indication, or dosage of over-the-counter medications.”

We stand by our conclusion that “the possibility that aspirin and NSAID [nonsteroidal antiinflammatory drug] use in pregnancy could lead to perinatal brain damage cannot be excluded” and wrote our article to point out what might be a hazard. However, the last sentence of our article emphasizes our recognition that our findings might reflect random phenomena; “since we are the first to our knowledge to identify this association, we encourage others to confirm or refute our findings.”