Two large studies have offered reassurance that commonly used classes of drugs – opioids and macrolide antibiotics – do not seem to be linked to major birth defects when taken during pregnancy.
In one analysis of data from 82,000 women in the US with two or more prescriptions for any opioid during the first trimester, researchers found no substantial increase in risk for most malformations.
This included no clinically meaningful increase in the risk of major birth defects overall, or in heart malformations, club foot or neural tube defects.
There was only a small possible increase in the risk of oral clefts – of around four to five additional cases per 10,000 pregnancies exposed to opioids in those first few months, according to a study published by the BMJ.
The researchers said previous research had been conflicting and the data drawn from 2.7 million pregnancies over a 15-year period would help doctors make choices about prescribing painkillers in women and counsel them about any small risk.
Separately, a second study on macrolide use has been carried out using a national Danish registry. It follows a UK study that suggested an increased risk of major birth defects if the drug is given in early pregnancy.
The new data, which included all pregnancies in Denmark between 1997 and 2016, found no link between the use of macrolides in the first trimester and the risk of major birth defects.
The researchers’ analysis of 1.2 million pregnancies, also published in the BMJ, found infants born with major birth defects occurred in 35 per 1,000 pregnancies exposed to macrolides – compared with 37 per 1,000 pregnancies exposed to penicillin and 33 per 1,000 unexposed pregnancies.
The study also found no link when looking at individual macrolides and specific birth defects according to organ systems.
Its findings differ from a recent UK study that reported an increased risk of major birth defects among 2,170 women who used macrolides in the first trimester compared with women who used penicillin, with an adjusted risk ratio of 1.55, prompting a note of caution over their use.
The researchers behind the Danish study concluded: ‘In contrast with a recent cohort study from the UK, we found no significantly increased risk of any of the 12 organ-specific subgroups of birth defects, including defects of the heart, and no evidence of significant associations for individual macrolides.
‘We believe that our data provide reassurance about the risk of major birth defects when treatment with macrolide antibiotics is needed during pregnancy. Our findings could help inform clinicians, patients, and drug regulatory authorities.’