Associations between aeroallergens, negative birth outcomes remain unclear

Some patterns have emerged regarding the effects of aeroallergens on pregnant women with respiratory allergies, but the clinical importance of these patterns remains unclear, according to study results.

“Climate change, as we all know, is one of the main important challenges in the 21st century. It affects air pollution and aeroallergens,” Irene Bartha, clinical research fellow in pediatric allergy in the department of women and children’s health at King’s College London, said during the presentation at the European Academy of Allergy and Clinical Immunology Hybrid Congress.

The burdens of these aeroallergens vary throughout the year, Bartha continued, with previous research indicating that exposures to aeroallergens affect perinatal outcomes such as preterm birth and low birth weight.

The retrospective study reviewed data from 32,579 pregnant women at a tertiary hospital in Madrid, Spain, between June 2010 and June 2018. This cohort included 583 patients with respiratory allergies such as allergic rhinoconjunctivitis and allergic asthma sensitized to aeroallergens.

“Mainly, 99% of them had allergic rhinitis, and 34% had asthma,” Bartha said.

The women with respiratory allergies had a median age of 35 years (interquartile range [IQR], 32-37), whereas the control group had a median age of 33 years (IQR, 30-37).

The researchers identified pollen allergens including Cupressus arizonica (Arizona cypress), Platanus acerifolia (London plane tree), Olea europaea (common olive) and timothy grass, which are present in Madrid. Bartha noted that pollen was the allergen that mainly sensitized the overall population, affecting 78.2% of those with respiratory allergies.

“We also included animal dander and house dust mite, but house dust mite is not as common in Madrid due to the climate and the geographical location,” Bartha said.

Overall, 14.8% of the respiratory allergy group and 9.9% of the control group experienced preterm birth (P < .0001), defined as birth before 37 weeks’ gestation. Similarly, 11.8% of the respiratory allergy group and 7.9% of the control group experienced low birth weight (P < .0001), defined as less than 2,500 g.

The researchers reported positive correlations between preterm delivery and pollen levels of Platanus acerifolia during the first trimester (P = .002) and timothy grass during the second trimester (P = .038). No statistical differences emerged in the control group.

Also, women with respiratory allergy experienced positive correlations between exposure to Platanus acerifolia in the first trimester and low birth weight (P = .01).

The researchers did not find any relationship between these aeroallergens and preterm delivery or low birthweight in singleton pregnancies. But there were positive correlations between exposure to Platanus acerifolia during the whole pregnancy (P = .005), Cupressus arizonica in the first trimester (P = .015) and timothy grass in the second trimester (P = .007) and both perinatal outcomes among twins.

“Respiratory allergy patients were older and had higher grades of preterm delivery and low birth weight,” Bartha said, adding that cofactors involving multiple gestations included female sterility and the need for in vitro fertilization, based on logistic regression.

In the control group, there were no statistical differences when preterm birth and low birth weight were compared among singleton pregnancies, but there was a positive correlation between timothy grass levels and low birth weight during the whole pregnancy (P = .029).

The researchers cautioned, however, that the positive aeroallergens all had low correlation coefficient values in both groups of women for preterm birth and low birth weight alike.

Despite the different patterns the researchers observed among women with and without respiratory allergies, they concluded that the clinical importance of these patterns is still unknown.

The researchers then hypothesized that immunological changes due to exposure to aeroallergens among pregnant women with allergies may play a key role in fertility and during pregnancy, particularly in multiple gestations. Other inflammatory mechanisms, however, could not be ruled out, the researchers continued.

“We still need further investigations,” Bartha said.