Prenatal air pollution exposure and growth: The role of placental mtDNA content

In this study, we used 333 mother-newborn pairs from the Spanish INMA study (Sabadell: n = 120; Gipuzkoa: n = 152; Valencia: n = 61). We used temporally adjusted land-use regression models to estimate exposure to nitrogen dioxide (NO 2 ). We estimated growth curves for femur length (FL), head circumference (HC), abdominal circumference (AC), biparietal diameter (BPD), and estimated fetal weight (EFW) during pregnancy (weeks 12-20, 12-32 and 20-32). DNA was extracted from placental tissue cells. Relative placental mtDNA content was measured using quantitative real-time polymerase chain reaction. Each 10 μg/m increment in prenatal NO 2 exposure was associated with a relative decrease in placental mtDNA content of 4.3% (95% confidence interval (CI): -7.4, -1.1%). BPD at 12-32 and 20-32 weeks was significantly associated with prenatal NO 2 exposure (during weeks 0-12, 0-20, 12-20 and 0-32). HC at 12-32 and 20-32 weeks was significantly associated with prenatal NO 2 exposure during weeks 20-32 and weeks 0-32. The other fetal growth parameters were not significantly associated with prenatal NO 2 exposure. Each interquartile range increase in placental mtDNA content was significantly associated with an increase of 5.2% (95% CI: 0.4, 7.8%) in BPD at weeks 20-32. Our results give an implication that prenatal air pollution exposure can impair fetal head growth. Furthermore, we showed that placental mtDNA content can play a role in this adverse effect.