To examine prenatal APAP exposure in relation to language development in offspring at 30 months of age.

A population-based pregnancy cohort study including 754 women who enrolled in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study in pregnancy week 8–13. Two exposure measures were used: (1) maternally reported number of APAP tablets taken between conception and enrollment; (2) APAP urinary concentration at enrollment. Language development at 30 months was assessed by nurse's evaluation and parental questionnaire, including the number of words the child used (<25, 25–50 and >50). Main study outcome; parental report of use of fewer than 50 words, termed language delay (LD).

59.2% of women enrolled in weeks 8–13 reported taking APAP between conception and enrollment. APAP was measurable in all urine samples and urinary APAP was correlated with the number of APAP taken during pregnancy (P<0.01). Language delay was more prevalent in boys (12.6%) than girls (4.1%) (8.5% in total). Both the number of APAP tablets and urinary APAP concentration were associated with greater LD in girls but not in boys. The adjusted odds ratio (OR) for LD among girls whose mothers reported >6 vs. 0 APAP tablets was 5.92 (95% confidence interval (CI) 1.10–31.94). The OR for LD in girls whose mothers’ urinary APAP was in the highest compared to the lowest quartile was 10.34 (95% CI 1.37–77.86). While it cannot be ruled out, our available data do not support confounding by indication.

Given the prevalence of prenatal APAP use and the importance of language development, these findings, if replicated, would suggest that pregnant women should limit their use of this analgesic during pregnancy.