Design: Multicentre prospective matched cohort with equivalence analysis
Population: 434 US children aged 18 to 30 months, 217 matched pairs
Primary outcome: Ages and Stages Questionnaire (ASQ-3) total score
Effect: 255 vs 260; adjusted median difference −3.4 (90% CI −9.8 to 3.0), equivalent

This prospective cohort from 14 US maternal-fetal medicine centres compared 434 children aged 18 to 30 months, born to mothers who had or had not received a COVID-19 mRNA vaccine during or within 30 days before pregnancy. Groups were matched on delivery site, date, insurance and ethnicity.

The Ages and Stages Questionnaire total score was equivalent between groups (median 255 against 260; adjusted median difference −3.4, 90% CI −9.8 to 3.0), within the prespecified equivalence margin of 10 points. There were no differences in secondary measures, including behaviour checklists and the autism screening checklist.

Parents still ask whether vaccination in pregnancy could affect their child's development. This gives a direct, reassuring answer from a well-designed equivalence study. The children were assessed by questionnaire rather than formal testing, and the age window cannot rule out effects that appear later, but there is no signal here.

Reassure parents that developmental scores at two years were equivalent after mRNA vaccination in pregnancy.
Continue routine developmental screening for all children regardless of maternal vaccination.
Note that autism screening scores showed no difference.
Encourage recommended vaccination in pregnancy where it is advised.

Why it matters

Developmental worry is one of the commonest reasons parents decline vaccination in pregnancy.

The statistics, in plain English

An equivalence study sets a margin in advance — here 10 points on the developmental score — and asks whether the whole confidence interval falls inside it. The interval (−9.8 to 3.0) did, so the groups were judged equivalent. A 90% interval is standard for equivalence testing.