Temporal variation in the acute effects of air pollution on blood pressure measured at admission to labor/delivery

Same day or recent air pollution exposure increases blood pressure in pregnant women. Temporal blood pressure variation associated with hourly air pollution is unstudied. We randomly selected 500 women (249 normotensive, 191 with hypertensive disorders, and 60 with chronic hypertension) with singleton pregnancies and blood pressure measured at labor/delivery admission from a large cohort, the Consortium on Safe Labor. Community multiscale air quality models estimated hourly air pollutant exposures for the admission hour (lag 0) and for the 24 h preceding labor/delivery admission (lags 1–24). Linear regression estimated the effect of 10 % increase in pollutants on blood pressure at each time point, adjusting for maternal characteristics, labor type, and time of day. Women with chronic hypertension had higher systolic blood pressure with exposure to particulate matter <10 μm (by 1.0–1.3 mmHg at 0–4 h), sulfur dioxide (by 0.7–0.9 mmHg at 0–3, 16–20, and 22–23 h) and with some air toxics. Diastolic blood pressure was higher in normotensive women with ozone exposure (by 0.1–0.4 mmHg at 0–1 and 23–24 h). Similar effects for systolic blood pressure were seen among women with hypertensive disorders (by 0.6 mmHg at 19–20 h), but most pollutants were associated with lower blood pressure in these women. Substantial variation in the impact of hourly air pollutant measures on blood pressure was observed during the day prior to labor/delivery admission, both by mothers’ hypertensive status and by the lag time prior to BP measurement. Effects were largest near admission (lags 0–4) and among women with chronic hypertension.