Pollen Exposure during Pregnancy may Lead to Asthma in Infants

Exposure to high levels of pollen during pregnancy escalates the risk of having a child with asthma, according to a new study.

Asthma is an inflammation of the air passage, leading to a narrowing of the airways that carry air from the mouth and nose to the lungs. It is one of the most common chronic conditions, affecting one in 20 American children.

Previous studies have shown that babies born during pollen season are more prone to develop allergies compared to other babies.  For the current study, a team of researchers led by Dr. Adrian Lowe from the Umea University in Sweden looked at 110,000 pregnant women living in the Stockholm area.

Factors like mother's smoking habits, the infant's gender and season of birth were taken into consideration. Of the total children, about 940 were hospitalized for asthma during the first year.

Researchers found exposure to high levels of pollen during the last 12 weeks before giving birth increasing the baby's risks of being hospitalized for asthma (35 percent) in the first year.

"Season of birth is associated with a range of differences in cord blood cytokine production profiles  and pollen may influence these patterns. It is likely that pollen sensitised mothers exposed to high levels of pollen during pregnancy are at increased risk of symptoms and asthma exacerbations. This may in turn change the intrauterine environment, predisposing the child to a Th2 type response," the authors wrote.

"Alternatively, symptomatic mothers during high pollen periods may have increased risk pregnancy complications, including pre-eclampsia, preterm birth and impaired foetal growth, which could influence the risk of wheezing illness."

Surprisingly, researchers found pregnant women who smoked heavily and were exposed to high levels of pollen during the first three months of pregnancy having a lowered risk compared to non-smoking mothers.

The findings of the study have been published in Allergy, Asthma & Clinical Immunology.