Birth by cesarean delivery raises allergy risk

Babies born by cesarean delivery are at higher risk for developing allergies than infants born vaginally, according to preliminary findings from a study funded by the Henry Ford Hospital, Detroit, Michigan, and the National Institute of Allergy and Infectious Diseases.

Researchers used a population-based birth cohort from the Wayne County (Michigan) Health, Environment, Allergy, and Asthma Longitudinal Study to identify 1,258 children born from 2003 to 2007 and evaluated them at 1, 16, 12, and 24 months for exposure to cockroach, dust mite, cat, and dog allergens in their homes.

Data were collected from the infants’ umbilical cord blood and stool, blood samples from both parents, mothers’ breast milk, and dust in the homes. It was also collected from family history of allergy or asthma, pregnancy variables, household pets, tobacco smoke exposure, babies’ illnesses, and medications used. Mode of delivery was confirmed from medical records.

When the infants’ blood samples were analyzed at 24 months for allergen-specific immunoglobulin E (IgE) antibodies, findings showed that babies born through cesarean delivery were 5 times more likely to have detectable allergens to dust mites, cats, and dogs than babies born vaginally.

Researchers hypothesize that babies’ exposure to bacteria in the maternal birth canal primes the development of their immune systems. Babies born by cesarean delivery lack certain microorganisms in their gastrointestinal tracts, which may make them more susceptible to developing IgE antibodies when exposed to allergens.

Although the study found an association between birth by cesarean and allergy risk, it did not prove cause and effect. However, researchers say their findings support the hygiene hypothesis that early exposure to microorganisms affects the development of babies’ immune systems and their sensitization to allergens by the time they are toddlers.

The study findings were presented at the annual meeting of the American Academy of Allergy, Asthma, and Immunology in San Antonio, Texas.