Residential radon exposure and hypertensive disorders of pregnancy in Massachusetts, USA: A cohort study.

Background: Exposure to ionizing radiation has been associated with hypertension, but the relationship between residential radon exposure and hypertensive disorders of pregnancy (HDP) has not been examined.

Methods: We used the Massachusetts Birth Registry of Vital Records from 2001 to 2015 including women with a singleton pregnancy without prior hypertension. The binary outcome (HDP) included gestational hypertension and pre-eclampsia cases and was assessed using birth certificate data. We obtained 141,665 basement radon measurements from Spruce Environmental Technologies, Inc. and modeled the monthly zip code basement radon level. We used a logistic regression model adjusted for sociodemographic covariates, maternal comorbidities, PM, season, temperature, and relative humidity. We examined effect modification by maternal age, race, and maternal education as an indicator of socio-economic status.

Results: Of 975,528 women, 3.7% (36,530) of them developed HDP. Zip code level radon ranged from 22 to 333 mBq/m. An interquartile range (IQR) increase in zip code radon level throughout pregnancy was associated with a 15% increase in the odds of HDP (95% CI 13% to 18%). In women less than 20 years old, an IQR increase in zip code level radon was associated with 38% increase in the odds of HDP (95% CI 24% to 50%), while the effect was smaller in older women. There was no effect modification by maternal race or education.

Conclusions: In this cohort, higher levels of residential radon are associated with increased odds of HDP. After stratifying by age, this effect was stronger in participants younger than 20 years old. Since the burden of hypertensive disorders of pregnancy is increasing and affects women's future cardiovascular health, identification of modifiable risk factors is of great importance.