Cesarean births are not likely linked to an elevated risk of food allergy during the first year of life, an Australian study found.
Published online in the Journal of Allergy and Clinical Immunology, the findings may help assess the risks and benefits of cesarean delivery and reassure women who require it that their babies are not more likely to develop food allergy, according to Rachel L. Peters, PhD, an epidemiologist at the Murdoch Child Research Institute (MCRI) in Melbourne, and colleagues.
Dr. Rachel L. Peters
Dr. Peters’ group undertook the analysis to clarify a possible association between mode of delivery and food allergy risk, which has remained unclear owing to the absence of studies with both challenge-proven food allergy outcomes and detailed information on the type and timing of cesarean delivery.
“The infant immune system undergoes rapid development during the neonatal period,” Dr. Peters said in an MCRI press release, and the mode of delivery may interfere with the normal development of the immune system. “Babies born by cesarean have less exposure to the bacteria from the mother’s gut and vagina, which influence the composition of the baby’s microbiome and immune system development. However, this doesn’t appear to play a major role in the development of food allergy,” she said.
The HealthNuts study
In the period 2007-2011, the longitudinal population-based HealthNuts cohort study enrolled 5,276 12-month-olds who underwent skin prick testing and oral food challenge for sensitization to egg, peanut, sesame, and either shellfish or cow’s milk. It linked the resulting data to additional birth statistics from the Victorian Perinatal Data Collection when children turned 6.
Birth data were obtained on 2,045 babies, and in this subgroup with linked data, 30% were born by cesarean – similar to the 31.7% of U.S. cesarean births in 2019 – and 12.7% of these had food allergy versus 13.2% of those delivered vaginally.
Compared with vaginal birth, C-section was not associated with the risk of food allergy (adjusted odds ratio [aOR] 0.95, 95% confidence interval [CI], 0.70-0.30).
Nor did the timing of the C-section have an effect. Cesarean delivery either before labor or after onset of labor was not associated with the risk of food allergy (aOR, 0.83, 95% CI, 0.55-1.23) and aOR, 1.13, 95% CI, 0.75-1.72), respectively.
Compared with vaginal delivery, elective or emergency cesarean was not associated with food allergy risk (aOR, 1.05, 95% CI, 0.71-1.55, and aOR, 0.86, 95% CI, 0.56-1.31).
Similarly, no evidence emerged of an effect modification by breastfeeding, older siblings, pet dog ownership, or maternal allergy.
“This study is helpful because in addition to blood and skin tests, it also used food challenge, which is the gold standard,” Terri Brown-Whitehorn, MD, an attending physician in the division of allergy and immunology at Children’s Hospital of Philadelphia, said in an interview. “If no actual food is given, the other tests could lead to false positives.”
Dr. Terri Brown-Whitehorn
Dr. Brown-Whitehorn, who was not involved in the MCRI research, said the findings are not likely to affect most decisions about C-sections because most are not voluntary. “But if a mother had a first baby by emergency cesarean section, she might be given the option of having the next one by the same method.”
She said the current advice is to introduce even high-risk foods to a child’s diet early on to ward off the development of food allergies.
According to the microbial exposure hypothesis, it was previously thought that a potential link between cesarean birth and allergy might reflect differences in early exposure to maternal flora beneficial to the immune system in the vagina during delivery. A C-section might bypass the opportunity for neonatal gut colonization with maternal gut and vaginal flora, thereby raising allergy risk. A 2018 meta-analysis, for example, suggested cesarean birth could raise the risk for food allergies by 21%.
In other research from HealthNuts, 30% of child peanut allergy and 90% of egg allergy appear to resolve naturally by age 6. These numbers are somewhat higher than what Dr. Brown-Whitehorn sees. “We find that about 20% of peanut allergies and about 70% or 80% – maybe a bit less – of egg allergies resolve by age 6.”
This research was supported by the National Health & Medical Research Council of Australia, the Ilhan Food Allergy Foundation, AnaphylaxiStop, the Charles and Sylvia Viertel Medical Research Foundation, the Victorian Government’s Operational Infrastructure Support Program, and the Melbourne Children’s Clinician-Scientist Fellowship.
Dr. Peters disclosed no competing interests. Several coauthors reported research support or employment with private companies and one is the inventor of an MCRI-held patent. Dr. Brown-Whitehorn had no competing interests to disclose.