A comprehensive new study shows that taking antibiotics during pregnancy increases the risk of the baby developing asthma by an average of 20 percent.
“Our research suggests that antibiotics affect the mother during pregnancy and thus the baby’s risk of developing asthma,” says Hans Bisgaard, a professor of paediatrics at Copenhagen University and the head of the the Danish Pediatric Asthma Center at Copenhagen University Hospital.
“More specifically, there is a strong indication that antibiotics/penicillin disturb the mother’s natural occurrence of bacteria, and that in some way or other this increases the risk of the baby developing asthma after birth.”
The new findings, based on data from more than 31,000 Danish children, have just been published in The Journal of Pediatrics.
“Our study indicates that taking antibiotics during pregnancy disrupts the mother’s microbiology, regardless of which stage in the pregnancy the mother took the antibiotics,” says the first author of the study, Lone Graff Stensballe, MD, PhD.
“We also observed that the more antibiotics the pregnant woman has taken, the higher the risk of the baby developing asthma,” she adds.
The researcher examined to which extent pregnant women had taken antibiotics during their pregnancy, and how often.
The first seeds of suspicion were sown when the researchers studied a unique group of 411 Danish children who have been monitored closely at the Danish Pediatric Asthma Centre (DPAC) since 1988 – the so-called COPSAC cohort (see Factbox). Here the scientists looked at antibiotics intake in the third trimester of pregnancy.
They then replicated their findings in an unselected national birth cohort, where they investigated antibiotics intake throughout pregnancy in a group of more than 30,000 Danes.
Both studies showed that when the pregnant woman had taken antibiotics, the child faced an increased risk of developing asthma.
“The results fit in well with DPAC’s other studies, which point to a crucial role for the bacterial environment that the child is exposed to in its very early life and the risk of subsequent asthma,” says Bisgaard.
The studies also showed that the more antibiotic treatment the mother had received, the greater the risk of child developing asthma.
The risk was about three times higher for children of women who had received four or more antibiotics treatments compared to children of women who had received only one antibiotic treatment.
The scientists also made adjustments for pregnant women who took antibiotics because they themselves had respiratory infections.
The children in the study come from two population studies.
Copenhagen Prospective Study on Asthma in Childhood (COPSAC) under the Danish Pediatric Asthma Center, which contains data on 411 Danish children of mothers with asthma.
Bedre Sundhed for Mor og Barn (Better Health for Mother and Child) at the State Serum Institute, which contains data on more than 100,000 Danish children, 30,675 of which were included in the study.
“We wanted to make sure that children didn’t get hereditary asthma, so we filtered our results for women who had been given antibiotics because they had weak lungs,” says Stensballe. “Even when we adjusted for this factor, the result remained that antibiotics increase the risk of asthma, and more antibiotics further increase the risk.”
The cause, says Stensballe, probably lies in the way the immune system develops in relation to bacteria:
When a baby is in the womb, it’s in a sterile environment. Their first contact with bacteria is when they’re born.
“Several studies indicate that exactly this very early contact with bacteria in the birth canal, from the mother and from the environment, are of great importance to the development of a healthy immune defence, which does not develop e.g. asthma,” she says.
“When a pregnant woman takes antibiotics, she’s not only fighting off an infection; she’s also changing her own microbial balance. This could mean that the baby does not get the bacteria required for developing a healthy immune defence. That could be the reason why they develop asthma.”
Backed by the new findings, Stensballe believes that doctors should think twice before prescribing antibiotics for pregnant women.
Doctors should be sure that antibiotics really are necessary in each individual case.
During the study, Lone Graff Stensballe was affiliated with the Department of Epidemiology Research at the Danish State Serum Institute.
She now works at the Women, Children and Reproduction Centre at the Copenhagen University Hospital.
“Many doctors will consider prescribing antibiotics if a pregnant woman for instance speaks of abdominal pain or painful urination,” she says.
“But it’s not certain that it’s a bacterial infection each time. Here we must encourage doctors to be less generous with antibiotics to pregnant women – to make sure they don’t prescribe it without even having checked if it has any effect.”
She is, however, keen to point out that there are of course many cases where antibiotics are necessary – for instance if it’s a urinary tract infection with bacteria. This infection can spread to the uterus and may cause premature birth.
“We should of course prescribe antibiotics in such cases,” she says.