Bandoli G, et al. - Because previous prenatal acetaminophen use studies did not address what indications and maternal co-factors describe the use of acetaminophen, researchers described these parameters in a well-characterized, prospective birth cohort. Statistics were taken from the 2004 to 2018 MotherToBaby study of pregnant women enrolled. Of 2,441 patients, 1,515 reported acetaminophen use. There was a decline in the use of 2.5% for each 2-year period with 58% reporting acetaminophen use in 2017-2018 over the 15-year period. Tobacco use, obesity, self-reported depression or anxiety, and antidepressant use were associated with increased duration of exposure. Nonetheless, the most frequently reported indication was a headache, indication varied by the duration of use, with more women reporting use for sleep or pain/injury in the longest-used categories. Of those reporting use for sleep, the median dose per exposed day was highest, and higher doses were reported more frequently for arthritis, injury, and pain. The majority of pregnant women use acetaminophen, and some continue to use it for many weeks during pregnancy. Given the heterogeneity in the duration of use, indication, and dose, studies that estimate the risk of acetaminophen-related adverse outcomes have to consider these factors carefully.