- Design
- Population-based cohort with propensity score weighting, two US insurance databases
- Population
- About 4.2 million pregnancies, 79,118 with first-trimester benzodiazepine exposure
- Primary outcome
- Any major congenital malformation
- Effect
- Pooled adjusted RR 0.99 (95% CI 0.96 to 1.03); 4.0% vs 4.1% and 4.9% vs 4.8%
The researchers used two large US insurance databases to compare pregnancies with at least one benzodiazepine prescription filled in the first trimester with unexposed pregnancies, adjusting for confounders using propensity scores.
Malformation risk was essentially identical in exposed and unexposed pregnancies in both databases. Organ-specific signals did not hold up across sensitivity analyses, and higher doses were not linked to more malformations.
Earlier studies had conflicting results, and fear of malformation drives abrupt cessation. This study does not address the third trimester, when neonatal effects are the concern, so planning remains necessary.
- Absolute malformation risk was about 4 to 5% in both exposed and unexposed pregnancies.
- There was no dose-response and no clear difference between individual benzodiazepines.
- Combinations with other psychoactive drugs gave inconsistent signals; review the whole regimen.
- Still plan taper or continuation deliberately, given risks of neonatal sedation and withdrawal near delivery.
- Document the counselling, including the background malformation risk.
Why it matters
Abrupt withdrawal and terminations driven by fear of malformations carry their own harms, and this is the largest dataset yet to address that fear.
Don't overread it
The study looked at malformations at birth only, not neonatal withdrawal, neurodevelopment or later-pregnancy use.
The statistics, in plain English
An RR of 0.99 with an interval from 0.96 to 1.03 rules out anything but a tiny effect. The authors set 1.3 as the threshold for a meaningful increase in advance, and the interval sits well below it. It is observational, so a prescription fill does not prove the drug was taken.
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