Babies born by Caesarean section have a greater risk of developing asthma as compared to babies born naturally, a new study has found.
The study was based on data from 1.7 million births registered at the Medical Birth Registry at the Norwegian Institute of Public Health.
The goal of the study was to look into the possible link between being born by Caesarean section and later development of asthma.
The researchers found that compared to children born in the natural way i.e. spontaneously and vaginally, children born by Caesarean section had an approximately 50 percent-increased risk of developing asthma.
Children born vaginally, but with assistance from vacuum or forceps, had a 20 percent increased risk of asthma.
The study also found that emergency Caesarean section was associated with a 60 percent increased risk.
"We found a moderately strong association between birth by Caesarean section and asthma in childhood," says doctor and research fellow Mette Christophersen Tollånes, who works for both the Norwegian Institute of Public Health and the Department of Public Health and Primary Health Care at the University of Bergen, Norway.
Tollånes explains that there are two main theories about why Caesarean sections could cause asthma.
The first is that babies who are born by Caesarean section are not exposed to their mothers' bacteria during birth, which is detrimental for development of the immune system. The other is that babies born by Caesarean section have more breathing problems after birth because they are less exposed to stress hormones and compression of the chest, since these mechanisms contribute to emptying the lungs of amniotic fluid.
Maybe this can negatively affect lung function in the long term. The fact that emergency Caesarean section apparently has a stonger effect on the risk of asthma than planned Caesarean section cannot easily be explained by any of these theories. It is possible that there are other common causes that can induce the need for Caesarean section and the development of asthma, says Tollånes.
The authors looked at over 1.7 million births reported to the Medical Birth Registry at the Norwegian Institute of Public Health in the period 1967-1998. Multiple births and children with congenital malformations were excluded. The children were monitored until they became 18 years old or through 2002.
The study compared the proportions of children who received a basic -and/or attendance benefit for asthma from the Social Security office after spontaneous vaginal birth, assisted vaginal birth (forceps or vacuum), and Caesarean section (planned Caesarean section and emergency Caesarean section separate from and including 1988), respectively.
The study is published in the Journal of Pediatrics.