The number of caesarean sections (CS) in the US was at 4.5% in 1965, the year it was first measured. Thereafter the rate increased steeply to a high of 32.9% in 2009 so that one in three mothers gave birth by caesarean section. The rate dropped to 32.8% in 2010. This trend in increased CS is seen worldwide and has occurred concurrent with a rising epidemic of
- autoimmune diseases (Crohn’s, multiple sclerosis and type 1 diabetes)
- allergic diseases (asthma, allergic rhinitis and atopic dermatitis).
C-section and asthma
The effect of CS has been associated with a significant increased rate in asthma, particularly in females, and allergic rhinitis.
An article in the Journal of Pediatrics reported on a population-based cohort study in Norway involving over a million children (1,756,700) born between 1967 and 1998. It was noted that the rate of CS had increased from a low of 1.7% in 1967 to a high of 11% in 1985 and 12% in 1998. The rate of asthma had also increased during those years. The objective was to find out if there was a link between CS (either planned or emergency) and the risk of asthma. Vaginal delivery (spontaneous or instrumental) acted as the control.
In this study the children were followed up to the age of 18 years or to the year 2002. Children excluded from the study were those who
- were in multiple gestation pregnancies
- had birth defects
- died before the age of one.
The researchers found that children delivered by C-section had a 52% increased risk of asthma compared with vaginal delivery’s 19% risk. In this comparison, the risk was lower (42%) if the C-section was planned but higher (59%) for an emergency C-section. (See table below.)
A C-section increased the risk of asthma, particularly for infants born at an earlier gestational age as well as with an emergency C-section. Thus the two factors that have a major influence on the risk of asthma due to a C-section include:
- early gestational age
- emergency C-section.
The explanation of the positive association between cesarean delivery and the risk for childhood asthma may be either due to lack of contact with the bacterial flora in the maternal birth canal or the increased risk for respiratory distress and transitory tachypnea in new born children.
C-section and atopy
A study in the Journal of Allergy and Clinical Immunology found evidence of the link between CS and atopy that is, hayfever and allergic sensitization. Pistiner and others found that birth by C-section increased the risk for allergic sensitization and hayfever among children whose parents had allergies or a history of allergic disease.
Pistiner and colleagues studied 432 children for the first 9 years of their lives. These children had parents with a history of allergic disease. After discounting factors such as exposure to cigarette smoke, birth weight and maternal age at birth, they found that children born by C-section had double the risk of becoming sensitized to common allergens and were 1.8 times more likely to develop hay fever or allergic rhinitis than those born vaginally.
This study did not see an increased risk of asthma in children born by C-section. The researchers suggested that lack of contact with microbes that would be present in a vaginal birth may explain the increased risk.
A more recent study on the association of CS and allergies involved 2216 children of age 8. After adjusting for confounders it was found that in children with a family history of allergies, if born by C-section, had a more than two-fold increase in the odds of being atopic. (OR 2.62) No such association was seen in children who did not have a family history of allergies (OR 1.16) The researchers concluded that CS are associated with both asthma and atopic sensitization in childhood particularly in children with a family history of allergies.