Maternal short-term exposure to NO₂ during pregnancy and its relationship with Doppler markers of placental function

Maternal exposure to air pollution has been associated with poor obstetric outcomes. However, the available evidence on the impact of maternal exposure to air pollution on placental function is still scarce and is based on estimated ambient levels of air pollutants.

To evaluate the association between short-term maternal exposure to NO₂ based on the objective personal measure of NO₂ exposure and Doppler markers of placental function.

This study was based on a prospective cohort of 101 pregnant women, recruited at Hospital Sant Joan de Déu, Barcelona (Spain), between January 2017 and April 2018. NO₂ diffusion tubes were worn by pregnant women to measure personal exposure to NO₂ between weeks 28 and 32 of their pregnancy. Placental function was evaluated at the 32nd week of gestation by Doppler evaluation of mean uterine arteries pulsatility index (PI), umbilical artery PI, middle cerebral artery PI, cerebroplacental ratio (CPR) and ductus venosus PI. Linear regression models were applied to estimate the association of personal NO₂ exposure and Doppler markers of placental function (one at a time), controlled for relevant covariates.

Higher personal exposure to NO₂ was significantly associated with lower mean uterine artery PI. Each one-interquartile range (IQR) increase in the exposure to NO ₂ was associated with -0.07 (95% confidence intervals (CIs): -0.12, -0.02) decrease in uterine arteries PI. We also observed some suggestions for an inverse association between this exposure and CPR. A one-IQR increase in NO₂ was associated with -0.18 (95% CIs: -0.37, 0.01) decrease in CPR. The findings for the rest of Doppler markers were not conclusive.

Maternal exposure to NO₂ could interfere with Doppler markers of placental function, potentially indicating a certain degree of cerebral vasodilatation with a decrease of mean uterine arteries PI.