Background Delivery by caesarean section has been identified as a risk factor for asthma. Meta-analyses have reported a 20% increased risk for childhood asthma or its common symptom – wheezing. However, asthma is a heterogeneous disease with distinct phenotypes portrayed as various wheezing trajectories. We sought to assess the relationship between mode of delivery at birth and three commonly identified wheezing trajectories of childhood, as well as additional asthma-related outcomes.

Methods Data were drawn from the UK Millennium Cohort Study and included 8744 participants who were singleton, born at term and healthy at the time of birth. Participating families were interviewed at infancy and at ages 3, 5, 7 and 11 years. Wheezing trajectories were examined through parental report of wheezing in the past year, which was coded as ‘transient’ (resolved by age 5) ‘persistent’ (both before and after age 5) or ‘late-onset’ (appearing starting age 5) compared to no report of wheezing. Relative risk ratios were estimated using multinomial logistic regression. Cross-sectional asthma-related outcomes of recent wheezing, severe recent wheezing, ever having asthma and asthma medication use were estimated using logistic regression.

Results Most of the children were born through unassisted vaginal delivery (72%); instrumental vaginal delivery, planned caesarean and emergency caesarean accounted for 10%, 9% and 10% of births respectively. The proportion of children exhibiting transient, persistent and late-onset wheezing was 11.6%, 11.1% and 12.9% respectively.

Children born by a medically interventional delivery had similar odds of experiencing transient wheezing compared to no wheezing as those born by unassisted vaginal delivery. The same was true for late-onset wheezing compared to none. The risk of experiencing persistent wheezing was higher in children born by planned caesarean compared to those born by unassisted vaginal delivery (RRR=1.33, 95% CI (1.02, 1.75)). Confounders accounted for were mother’s age, education, marital status, socioeconomic position, smoking and parents’ asthma in addition to child’s sex, ethnicity, gestational age, birthweight and being firstborn. After adjustment, the elevated risk for persistent wheezing in the planned caesarean group remained unchanged and marginally significant (RRR=1.32 95% CI (1.00, 1.75)).

No consistent pattern of association between mode of delivery and additional asthma-related cross-sectional outcomes was found.

Conclusion Birth by planned caesarean section may be a risk factor for persistent wheezing in childhood, but not for the transient or late-onset trajectories of wheezing. However, the strength of evidence is low due to multiple comparisons and the absence of a consistent trend of associations with additional asthma-related outcomes.