There is a worldwide trend towards increasing rates of Caesarean section. In the UK, Caesarean section accounted for 2% of all births in 1953, 18% in 1997 and 21% in 2001.1 Marked differences are reported in rates from different healthcare sectors, reaching almost 50% in some private hospitals.1 There is insufficient understanding of why women may request a Caesarean section in the absence of a medical reason. The convenience for the caregiver, the age, personal and birth experience and the working field of the gynaecologists influence the way they council their patients. However, both the physician and the mother should take into account all risks and benefits for the health of the mother and the infant. An increased risk of allergy in the offspring is one of the debated side effects of Caesarean section.
The clinical data on an increased risk for allergic manifestations during early childhood are conflicting. Two independent prospective cohort studies found a positive association between allergic sensitisation against food allergens and inhalant allergens with Caesarean section.2 ,3 In the German Infant Nutritional Intervention Program (GINI) study, healthy full-term neonates with at least one parent or sibling with self-reported allergic disease were enrolled.4 The analysis looking at the influence of mode of delivery was restricted to 889 infants exclusively breast-fed during the first 4 months of life in order to exclude the effect of formula feeding. The rate of Caesarean section was 17% (147/865). There was no difference between the two groups of infants with respect to maternal history of allergy (70.8% vs 70.1%), maternal asthma (15.0% vs 13.8%), parental education and rural place of residence. After adjustment for these and other possible confounders infants born by Caesarean section more often had episodes of diarrhoea (adjusted odds ratio (ORadj) 1.45, 95% CI 1.00 to 2.10, with the highest effect during the first 4 months of life) and sensitisation to food allergens both in adjusted (ORadj 2.05, 95% CI 1.10 to 3.8). No association with atopic dermatitis was found.2 In the second study, data from 2500 participants of the LISA cohort were analysed with a follow-up of 2 years.3 Caesarean delivery was associated with at least one episode of wheezing (ORadj 1.31, 95% CI 1.02 to 1.68), recurrent wheezing (1.41; 1.02 to 1.96), allergic sensitisation against food allergens (1.64; 1.03 to 263) and against inhalant allergens (1.75; 0.08 to 3.12). No association was found regarding atopic dermatitis. In a population-based cohort of 2803 children from Norway, a sevenfold increased risk for parentally perceived reaction to egg, fish, or nuts was also reported in 2-year-old children whose mothers were allergic.5 Egg allergy was confirmed four times more often. The effect was much weaker in children with a hereditary background. In the same cohort, an association between Caesarean section and persistent verified cow’s milk allergy was found.6 The effect was strongest in children with maternal allergy.
Surprisingly, neither the studies in young children up to the age of 2 years2,5,6 nor in older children and adults7⇓9,10–11 observed a significant association of the mode of delivery with atopic dermatitis. In contrast, the risk of allergic rhinitis and/or asthma was increased, at least in some of the studies. Although the effect size in most studies was modest, in the face of the high prevalence of allergic diseases in industrialised societies, this translates into a substantial excess burden of morbidity.