Summary: A large U.S. study of more than 8,900 mother–infant pairs found no evidence that acetaminophen (Tylenol) taken during pregnancy increases the risk of preterm birth or alters average birth weight. After rigorous statistical adjustments, the research team at the UNC Gillings School of Global Public Health reports no association with preterm birth, birth weight, or being small-for-gestational-age (SGA). The analysis did identify a modest association with lower odds of delivering a baby classified as large-for-gestational-age (LGA) when weight was considered relative to gestational week.
Key Facts
- No link to earlier birth or lower birth weight: After adjusting for demographic and clinical factors, the researchers found no statistically significant relationship between prenatal acetaminophen use and timing of delivery or average birth weight.
- Four primary birth outcomes examined: The study evaluated the association between maternal acetaminophen use and:
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- Preterm birth — no significant association observed.
- Birth weight — average birth weight did not differ meaningfully between exposed and unexposed groups.
- Small-for-gestational-age (SGA) — no elevated risk detected.
- Large-for-gestational-age (LGA) — a statistically significant association with lower odds of LGA was observed for those reporting acetaminophen use.
- LGA finding: When birth weight was analyzed relative to exact week of delivery, maternal acetaminophen use was associated with a reduced likelihood of giving birth to an infant classified as LGA.
- Practical reassurance with standard use: The lead author emphasizes that these conclusions apply to acetaminophen used as directed. Pregnant people should continue to consult their prenatal clinicians about dosing, duration, and whether acetaminophen is appropriate for their individual situation.
Source: UNC
In brief: New research led by environmental scientists at the UNC Gillings School of Global Public Health found no statistically significant evidence that acetaminophen use during pregnancy increases the risk of preterm birth or negatively affects birth weight. The findings, drawn from the NIH ECHO cohort and recently published in the American Journal of Epidemiology, also point to lower odds of delivering an LGA infant among those who reported prenatal acetaminophen use.
Acetaminophen is one of the most commonly used over-the-counter medications during pregnancy, often recommended for fever and pain relief when other analgesics are discouraged. Previous smaller or inconsistent studies produced mixed messages about potential effects on fetal development and birth outcomes. This larger-scale analysis was designed to provide clearer evidence using real-world data from a broad U.S. cohort.
The research team, led by senior author Rebecca Fry, PhD, and first author Katelyn Huff, PhD, analyzed data from 8,957 mother–infant pairs enrolled in the NIH’s Environmental influences on Child Health Outcomes (ECHO) program across 36 pediatric study sites. About 59% of participating mothers (n = 5,257) reported using acetaminophen at some point during pregnancy. The investigators used multiple imputation, inverse probability weighting, and regression modeling to account for potential confounders and to examine associations with four birth outcomes: preterm birth, birth weight, SGA, and LGA.
Key results showed no meaningful association between prenatal acetaminophen use and preterm birth, average birth weight, or SGA status after adjustment for relevant covariates. The adjusted models did, however, identify lower odds of LGA among those who used acetaminophen during pregnancy. These findings provide evidence that routine, directed use of acetaminophen does not appear to increase baseline birth risks for timing or low birth weight, while raising an intriguing observation about LGA that warrants further research.
Although the results are reassuring for common, guideline-consistent use, the authors underscore that this study does not endorse high or prolonged dosing without medical supervision. Future work should investigate dose–response relationships, trimester-specific exposure windows, and potential long-term developmental outcomes in offspring.
Key Questions Answered:
A: When a medication is used by roughly 60% of pregnant people, even very small risks can translate into important public health concerns. Because alternatives such as ibuprofen and aspirin are often avoided in late pregnancy, acetaminophen remains a primary over-the-counter option. Prior smaller studies gave mixed results; using the NIH ECHO database allowed investigators to analyze nearly 9,000 mother–infant pairs and provide more robust, population-level clarity.
A: LGA refers to infants whose birth weight is in the top 10% for babies born in the same week of gestation. True LGA can complicate delivery and indicate metabolic stress. The study found lower odds of LGA among mothers reporting acetaminophen use. The research was not designed to determine causation, but one hypothesis is that treating maternal fever and inflammation may reduce inflammatory drivers of excessive fetal growth.
A: No. The study supports that standard, directed use of acetaminophen for common pain and fever management was not associated with increased risk of preterm birth or low birth weight in this cohort. It does not validate unrestricted or high-dose use. Pregnant individuals should follow dosing guidance from their prenatal care provider and avoid prolonged or excessive use without medical oversight. Additional research is needed on high doses, long-term exposure, and developmental outcomes.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal article was reviewed in full by the editorial team.
- Additional context was added by staff for clarity.
About this neurodevelopment research news
Author: Meg Palmer
Source: UNC
Contact: Meg Palmer – UNC
Image: The image is credited to Neuroscience News
Original Research: Open access. “Prenatal over-the-counter acetaminophen use and birth outcomes in the ECHO Cohort” by Katelyn K Huff et al., American Journal of Epidemiology. DOI: 10.1093/aje/kwag110
Abstract
Prenatal over-the-counter acetaminophen use and birth outcomes in the ECHO Cohort
Acetaminophen is a widely used over-the-counter medication in pregnancy. Prior experimental and epidemiological findings have been inconsistent, motivating further investigation. To address this, the investigators assessed associations between prenatal acetaminophen use and birth outcomes in a large, multi-site U.S. cohort.
The study included 8,957 mother–infant pairs from 36 pediatric study sites participating in the NIH ECHO program. After performing multiple imputation and applying inverse probability weighting, regression models examined relationships between any acetaminophen use during pregnancy and four outcomes: (1) preterm birth, (2) birth weight, (3) small-for-gestational-age (SGA), and (4) large-for-gestational-age (LGA).
Approximately 59% of mothers (n = 5,257) reported acetaminophen use at any point in pregnancy. After adjusting for covariates, prenatal acetaminophen use was associated with lower odds of LGA (adjusted odds ratio [aOR]: 0.87; 95% CI: 0.79, 0.96). There was no association with preterm birth (aOR: 0.99; 95% CI: 0.86, 1.14), average birth weight (adjusted β: −7.52 g; 95% CI: −27.80, 12.77), or SGA (aOR: 1.02; 95% CI: 0.88, 1.18). The authors recommend future research to evaluate dose–response effects, trimester-specific exposures, and individual susceptibility factors.