According to new research, antibiotics taken during pregnancy do not raise the risk for most birth defects, though there are some exceptions.

Penicillin, the most commonly used antibiotic during pregnancy, including other widely prescribed antibiotics like erythromycin, cephalosporins and quinolones, have no association with increased risk for about 30-birth defects.

However, two types of antibiotics i. e. nitrofurantoins and sulfonamides or sulfa drugs that are given for urinary tract and other infections, have been linked with a higher risk for several birth defects.

The study found women whose children had a fatal malformation of the skull and brain (anencephaly), had taken sulfonamides during pregnancy. Sulfonamides have also been tied to an increased risk for heart defects like hypoplastic left heart syndrome and coarctation of the aorta, transverse limb deficiency and diaphragmatic hernia, choanal atresia (a blockage of the nasal passage), an abnormal opening in the diaphragm resulting in severe breathing difficulties.

Multiple birth defects, including anophthalmia and microphthalmos (eye defects) and several congenital heart defects have also been associated with Nitrofurantoins. Mothers of children born with cleft lips or palates were twice as likely to have taken nitrofurantoins.

However, Krista Crider, the study's lead author and a geneticist with the National Centre on Birth Defects and Developmental Disabilities, which is a part of the U. S. Centres for Disease Control and Prevention (CDC) said, pregnant women need not be overly concerned about taking antibiotics for treating infections during pregnancy.

'The most important message is that most commonly used antibiotics do not seem to be associated with the birth defects we studied,' Crider said.

The study's findings will be published in the November issue of Archives of Paediatrics & Adolescent Medicine, though the study did not look at chromosomal defects, including Down syndrome.