Sasha Milbeck, National Center for Health Research
The rate of Caesarean sections (C-sections) in the United States is on the rise and has increased over 50% since the 1990s.  In 2018, 31.9% of all births were C-sections  which is 3 times higher than the World Health Organization’s “ideal rate” for use as a necessary medical procedure to reduce maternal and newborn mortality.  As the rate of C-sections has grown, the incidence of certain chronic and immune system-related medical conditions has also greatly increased. Experts are asking whether this is a coincidence or do babies born via C-section have weaker immune systems?
This article will describe research studies that have linked C-sections with numerous health disorders. It is important to note that just because a connection exists, it does not mean that a baby born via C-section will develop a particular medical condition.
How Bacteria Support Your Immune System
A key difference between babies born vaginally compared to those born via C-section is bacteria. When babies are born, they are exposed to numerous microorganisms from their mother and the environment, and those microorganisms help develop the baby’s immune system and microbiome. In vaginal delivery, babies pass through their mother’s birth canal and are exposed to the mother’s fecal and vaginal bacteria.
This bacterial exposure is thought to help babies develop their immune system through a theory called “oral tolerance.”  The theory of oral tolerance suggests that the immune system is less sensitive to antigens (toxins and foreign substances such as bacteria) that your body has already experienced. The theory suggests that this early exposure helps the baby develop a healthy immune system and microbiome.
The microbiome is the collection of microorganisms that live in our intestines, skin, and the vagina, and help support our normal daily functions. Microbiome research is a very new research field, and numerous studies have associated a healthy microbiome with disease prevention and immune system support. [6,7] To learn more about the different microorganisms that live in and interact with your body, click here.
Since babies born via C-section do not pass through the birth canal and are not exposed to the same bacteria as babies born vaginally, their microbiome develops differently and has different strains of bacteria. In 2019, the largest ever study of newborns’ microbiomes was published in the scientific journal Nature.  The study analyzed nearly 600 births in the United Kingdom and found that children born vaginally have very different gut microbiomes compared to babies born via elective (those that are not medically necessary) C-section. The study found that C-section babies lack strains of gut bacteria found in healthy children and adults, and instead, their guts have higher amounts of harmful microbes that are common in hospitals and operating rooms. These differences could possibly put babies born via C-section at greater risk for certain immune diseases and health conditions.
Health Issues Among Babies Born Via Caesarean Section
Numerous recent research studies suggest that babies born via C-section are at higher risk for developing medical conditions. In this article, we will summarize recent research and provide you with information you can use to make informed health decisions.
Immune Disorders in Babies Born Via C-Section
A major study published in 2020 in the Journal of Clinical Epidemiology compiled over 30 years of data from two Danish registries, and examined the development of chronic immune and inflammatory diseases in over 2 million children born by C-section and vaginal delivery. Both female and male babies born via C-Section were significantly more likely to develop diabetes, arthritis, Celiac disease, and inflammatory bowel disease, compared to babies delivered vaginally. The babies were followed until they were 40 years old, and the increased risk of these inflammatory diseases was still present 40 years after delivery.
The findings of the Danish study are consistent with numerous smaller studies conducted in the United States that reported correlations between C-Sections and allergic/immune disorders. A study from 2005 reported on nearly 9,000 children in Oregon diagnosed with common nasal allergies, asthma, allergic skin reactions or eczema, and food allergies.  Children born via C-Section were significantly more likely to develop nasal allergies compared to those delivered vaginally. Females born via C-Section were more likely to develop asthma than those delivered vaginally. More research is needed before any conclusions can be made about the impact of C-Section on boys’ asthma.
Asthma in Babies Born Via C-Section
Nearly 2000 studies (including the 2005 study mentioned above) were reviewed to determine if babies born via C-section were more likely to develop asthma.  The results showed that C-sections (overall, elective, and emergency) significantly increased the risk of childhood asthma. The authors suggest two possible causes for the results: 1. Babies born via C-section are not in contact with mother’s vaginal and fecal bacteria. These bacteria might be necessary for the growth and development of the immune system and asthma prevention. 2. During vaginal delivery, babies squeeze through the birth canal and empty their lungs of amniotic fluid, in preparation for breathing air. Babies born via C-section are born with extra fluid in their lungs, which makes them more likely to develop respiratory problems.  While there is an association between C-section delivery and childhood asthma, there are numerous other possible causes for asthma. To learn more about how habits can predispose children to asthma, click here.
Obesity and Diabetes in Babies Born Via C-Section
Women born via C-section were also found to be more likely to develop obesity and Type II Diabetes as adults. A 2020 study published in the Journal of the American Medical Association compiled data from more than 33,000 women who were born between 1946 and 1964 who participated in the Nurses’ Health Study II.  Of the women in the study, 3.3% were born by C-section (whether medically necessary or not). Results showed that a Type II Diabetes diagnosis was significantly more likely in women born by C-section compared to those born vaginally. Women born by C-section were also more likely to develop obesity. Researchers suggest that since babies born via C-section have differences in their gut bacteria, they may have fewer bacteria shown to protect against obesity, such as Bifidobacteria and Bacteroides. 
Infection in Babies Born Via C-Section
While most studies in the past linked C-sections to risks of specific health conditions, a November 2020 study compiled data from over 7 million births in Denmark, Scotland, England, and Australia from 1996 to 2015, and investigated whether type of delivery was associated with infection-related hospitalizations in early childhood.  The results demonstrated that children born via C-section were more likely to develop all types of clinical infections, especially gastrointestinal (related to the stomach and intestines), respiratory, and viral infections. The increased risk continued until the children were 5 years old. The authors suggest that differences in microbiomes between babies born via C-section compared to vaginal birth could be a potential explanation for the study findings. Bacteria from the mother and the environment both colonize the baby’s microbiome at birth and can affect the baby’s development of a healthy immune system.
Numerous studies have linked C-sections with health conditions. Because many of these studies are small and presenting initial results, no conclusions have been made about whether C-sections actually result in a greater risk for medical conditions. For many mothers and babies, a C-section is still the safest option for delivery, but it is well established that many C-Sections performed in the U.S. are not medically necessary. If you are considering a C-section, talk to your physician about the possible impact on your baby’s healthy immune system.
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