Owning a dog while pregnant appeared to shape children’s immune systems well into adolescence, a researcher reported.

In a cohort of 1,193 mother-child pairs in southeast Michigan, the area under the curve for immunoglobulin E levels over ages 10-14 (“IgE trajectory”) was 28.8% lower in children with prenatal pet exposure vs children whose mothers kept no pets (P<0.001), reported Jasmine Alsukhon, MD, of the Henry Ford Health System in Detroit.

The association was mainly driven by dog ownership, which was associated with 26.7% lower IgE trajectory (P=0.0005). Cat ownership, on the other hand, was not significantly associated with IgE trajectory, she said at the virtual American College of Allergy, Asthma & Immunology meeting.

“The association of prenatal pet exposure with IgE trajectory was previously described in these same subjects through the age of 2 and this persisted through their teen years,” Alsukhon said in an online presentation of her findings.

Higher IgE is associated with increased allergen sensitization and subsequent conditions like atopic dermatitis and asthma.

Although it’s unclear whether this benefit would occur if parents acquired a pet after their child’s first year of age, the findings support the “hygiene hypothesis,” commented Jay Portnoy, MD, of Children’s Mercy Hospital in Kansas City, Missouri, who was not involved in the research.

Dogs, in particular, bring bacteria from outside into the home, which could influence a child’s microbiome early on in development. Dog ownership in pregnancy has also been linked to reduced risk of eczema in children.

“Exposure to pets also increases exposure to bacteria that could drive the immune system to mature and avoid developing allergies,” Portnoy told MedPage Today in an email.

The so-called Wayne County Health, Environment, Allergy and Asthma Longitudinal Study (WHEALS) started enrolling pregnant women in the Henry Ford Health System in 2003. Throughout the study, children averaged three IgE measurements, Alsukhon said.

Mothers’ mean age was 29.7 at delivery, and close to half were African American (45%). About 30% of mothers had allergy histories, 16% smoked, and 31% had environmental tobacco exposure during pregnancy.

A significantly higher proportion of mothers in the pet exposure group smoked compared to the non-exposed group (16% vs 9%, P<0.001), Alsukhon reported.

Lastly, children born to African-American mothers saw less of a reduction in IgE levels compared to children born to mothers of other races and ethnicities (11.3% vs 33.6%), while children delivered through cesarean delivery had lower IgE trajectories compared to children delivered vaginally (46.2% vs 18.1%), Alsukhon reported.