A big data study of benzodiazepine use shows it is linked to an increased risk of miscarriage, but an Australian expert remains unconvinced.

It is the first time different classes of benzodiazepines — including short-acting agents (such as temazepam or lorazepam) and long-acting agents (such as diazepam or clonazepam) — as well as duration of use have been quantified.

The Canadian observational cohort study of more than 400,000 pregnancies has found that, compared with non-use in matched controls, any filled benzodiazepine prescription nearly doubles the risk of miscarriage (OR 1.85).

In the study, just over 27,000 pregnancies ended in a miscarriage, including 375 among women exposed to the drugs in early pregnancy.