What’s wrong with the Cesarean section rumor? A twin study shows there must be other reasons for asthma.
Today almost every third woman gives birth by cesarean section. There are many reasons for this. Those giving birth are getting older and older, and births are more and more frequently associated with risks due to previous illnesses of the pregnant women. On the other hand, interventions have become safer and easier to plan, which is especially pleasing for clinics. And so there are many women who today consciously choose a Cesarean section without compelling reasons, despite the risk of pain, wound healing disorders, infections, adhesions, or complications in future pregnancies. In addition, there are possible long-term consequences of a C-section, such as an increased risk of asthma. But can a C-section really lead to a chronic respiratory disease?
A Danish study on twins (1) now gives some the all-clear. Mathematically, the connection between cesarean sections and asthma cannot be argued away. Studies have shown time and again that children who were born by cesarean section later suffer from asthma more frequently than those who were born naturally, i.e., through the birth canal.
A team headed by Astrid Sevelsted, for example, examined the data of 1.9 million Danish children born on the calculated date of birth between 1977 and 2012 for one of the largest studies of its kind (2). The researchers followed their development from birth to the age of 15. The risk of developing asthma was 23 percent higher in children who were delivered by C-section.
But is this connection also “real,” or are completely different factors responsible for this result? In order to investigate this, the researchers around Nis Brix (1) now concentrated on pairs of twins, the first of which was born naturally and the second via an emergency C-section. The researchers found 464 of such pairs of twins (out of a total of 42,628 twin births), i.e., about 1% of all twin births. 72 twins suffered from asthma. 30 of them were born the natural way, and 20 via an emergency Cesarean section; the siblings remained healthy in both cases. In 11 sibling pairs, both twins developed asthma. When scientists considered factors that could influence the outcome, such as birth weight, sex, or the need for ventilation, there was no difference in disease incidence between the two groups. Although this study is not large, it suggests that factors other than Cesarean sections are responsible for the correlations measured in other studies.
The pediatrician Catarina Almqvist from the Astrid Lindgren Children’s Hospital in Stockholm (3) also believes in this. She compared the data of 87,000 pairs of siblings, all of whom were born by C-section. Unlike the study above, the risk of asthma was increased only in children with an emergency C-section after an unfavorable natural birth, but not after an elective C-section, which was planned. Mette Tollanes also came to a similar conclusion in 2008 (4). All these studies suggest that other factors, such as maternal diseases, increased the child’s risk and not the Cesarean section itself.
Above all, however, the studies refute the assumption that a Cesarean section may alter the bacterial colonization of infants in such a way that they are more likely to develop asthma later on. Scientists had suspected in recent years that an altered bacterial spectrum after a Cesarean section could be responsible for higher asthma rates. Why? Because a baby is normally colonized with its mother’s bacteria as it passes through the birth canal. In a C-section, on the other hand, the baby is first and foremost exposed to the skin germs of the surgical staff and the mother as well as to the germs of the operating theatre. The composition of the bacteria between children born so differently, therefore, differs considerably in the first three months, but afterward, they adapt (5). It is also known that bacteria train the immune system.
However, the differences do not seem to be responsible for the development of asthma according to these studies. Therefore, much more research is needed for a final answer.
This is part 22 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website. Translation was done with the assistance of DeepL translator.
- Brix N, Stokholm L, Jonsdottir F, Kristensen K, Secher NJ. Comparable risk of childhood asthma after vaginal delivery and emergency caesarean section. Dan Med J. 2017;64(1): A5313.
- Sevelsted A, Stokholm J, Bønnelykke K, Bisgaard H. Cesarean section and chronic immune disorders. Pediatrics. 2015;135(1):e92-8.
- Almqvist C, Cnattingius S, Lichtenstein P, Lundholm C. The impact of birth mode of delivery on childhood asthma and allergic diseases–a sibling study. ClinExp Allergy. 2012;42(9):1369-76.
- Tollånes MC1, Moster D, Daltveit AK, Irgens LM.Cesarean section and risk of severe childhood asthma: a population-based cohort study. J Pediatr. 2008;153(1):112-6.
- Rutayisire E, Huang K, Liu Y, Tao F. The mode of delivery affects the diversity and colonization pattern of the gut microbiota during the first year of infants’ life: a systematic review. BMC Gastroenterol. 2016;16(1):86.