Taking an antibiotic for a common health problem during pregnancy could increase the risk of a baby having devastating birth defects, a study suggests. 

American scientists found that taking a specific kind of medication for a urinary tract infection (UTI) significantly increased the odds of baby being born with a congenital problem.

These issues ranged from a cleft palate to potentially serious problems with a baby's heart. 

UTIs—infections which affect the tube where urine exits the body (the urethra), bladder, or kidney—are particularly common in pregnant women. 

They are considered serious infections for expectant mothers as they can cause devastating consequences for both woman and baby. 

But now experts have found an antibiotic medics prescribe to clear UTIs could have health complications of its own. 

Called trimethoprim, researchers found the risk of birth defects in the woman taking the drug in their first trimester was 26.9 per 1,000 infants.

This translated to about one out of every 145 more patients having a baby with a congenital anomaly that they would otherwise. 

Such defects included 'severe' heart malformations as well as cleft lip and palates. 

In contrast, the risk posed by other antibiotics was lower, with only 19.8 to 23.5 malformations per 1000 infants. 

The researchers said this figure was in line with the standard chances of a baby having a birth defect, meaning there was no 'elevated risk' from other antibiotics used to treat UTIs. 

Trimethoprim is prescribed about 130,000 times in England per month. 

Women in the study—aged between 15 and 49—had either been prescribed a strong, specialised antibiotic such as nitrofurantoin, trimethoprim, or fluoroquinolone or a 'standard' antibiotic, such as penicillin.

Dr Caroline Ovadia, an expert obstetrics at the University of Edinburgh, who was not involved in the study said previous research suggested trimethoprim blocked a key nutrient in pregnancy.

'Trimethoprim can block the action of folic acid, which we know is important in early fetal development,' she said. 

UTIs are among the most common infections in pregnancy, affecting up to 10 per cent of all pregnant women.

This is roughly double the prevalence compared to non-pregnant women of the same age. 

Left untreated, they have been connected to premature births, low birth rate, kidney infections, and even sepsis. 

While UTIs classically cause symptoms like a burning sensation they can be asymptomatic meaning they are hidden infections causing no obvious problems but still still increasing the risk of complications. 

This is why pregnant women in Britain offered a urine test, to check for such hidden UTI at their first midwife appointment, which typically happens at around 10 weeks. 

In the US, the test is performed slightly later, between 12 and 16 weeks.