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Acetaminophen Use in Pregnancy and Risk of Birth Defects: Findings From the National Birth Defects Prevention Study

OBJECTIVE: To investigate whether exposure during the first trimester of pregnancy to single-ingredient acetaminophen increases the risk of major birth defects. METHODS: Data from the National Birth Defects Prevention Study, a population-based, case–control study, were used. Women who delivered between January 1, 1997, and December 31, 2004, and participated in the telephone interview were included. Type and timing of acetaminophen use were assigned based on maternal report. Women reporting first-trimester acetaminophen use in a combination product were excluded, resulting in a total of 11,610 children in the case group and 4,500 children in the control group for analysis. RESULTS: The prevalence of first-trimester single-ingredient–acetaminophen use was common: 46.9% (n=5,440) among women in the case group and 45.8% (n=2,059) among women in the control group (P=.21). Overall, acetaminophen was not associated with an increased risk of any birth defect. Among women reporting a first-trimester infection and fever, use of acetaminophen was associated with a statistically significantly decreased odds ratio (OR) for anencephaly or craniorachischisis (adjusted OR 0.35, 95% confidence interval [CI] 0.08–0.80), encephalocele (adjusted OR 0.17, 95% CI 0.03–0.87), anotia or microtia (adjusted OR 0.25, 95% CI 0.07–0.86), cleft lip with or without cleft palate (adjusted OR 0.44, 95% CI 0.26–0.75), and gastroschisis (adjusted OR 0.41, 95% CI 0.18–0.94). CONCLUSION: Single-ingredient–acetaminophen use during the first trimester does not appear to increase the risk of major birth defects. It may decrease the risk of selected malformations when used for a febrile illness. LEVEL OF EVIDENCE: II