The use of frequently prescribed antibiotics in early pregnancy has been linked by researchers to an increased risk of major birth defects.
Macrolide antibiotics are widely used to treat common bacterial infections, often as an alternative for patients allergic to penicillin.
Experts have urged caution in their use during pregnancy and said alternatives should be prescribed if possible.
Researchers at University College London analysed data on 104,605 children born in the UK between 1990 and 2016 to assess the association between macrolide antibiotics and major malformations.
They also looked at whether there was a link to their use and neuro-developmental disorders, including cerebral palsy, epilepsy, ADHD and autism.
In the children of women prescribed macrolides during their pregnancy, 186 out of 8,632 had major malformations, they found.
This compares to 1,666 out of 95,973 children of mothers who received penicillin.
After accounting for other factors, they found that macrolide prescribing during the first three months of pregnancy was associated with an increased risk of major malformation compared with penicillin - 28 v 18 cases per 1,000 - particularly heart defects.
They found no association when women were prescribed macrolides later on in the pregnancy.
And they observed no significant link to any of the four neuro-developmental disorders.
But they found macrolide prescribing in any trimester was associated with a slightly increased risk of genital malformations.
The authors warned women should not stop taking antibiotics when needed, as untreated infections are a greater risk to the unborn baby.