The evidence that maternal use of nicotine replacement therapy (NRT) is safe for the fetus is insufficiently robust, although use of the products is likely to be safer than smoking, according to authors of a review.

In their systematic review and meta-analysis, the researchers believe they have, for the first time, brought together all the observational studies on the topic to be assessed alongside the randomised controlled trial (RCT) data.

But findings from the 23 observational studies included — with more than 930,000 pregnant smokers as participants — were inconclusive, with confidence in the results “very low”, the researchers said.

“Findings from meta-analyses for congenital anomalies, stillbirth and preterm birth were underpowered and not in a consistent direction,” the authors wrote in Addiction.