Fetal growth and air pollution - A study on ultrasound and birth measures

- Largest study on ultrasound measures and air pollution to date.
- Individual data on potential confounders (also SES) and nitrogen oxides.
- Area with levels below current WHO air quality guidelines.
- Birth weight was reduced by 9 g per 10 µg/m3 increment of NOx.
- Small but statistically significant effects of air pollution on late fetal size.

Air pollution has been suggested to affect fetal growth, but more data is needed to assess the timing of exposure effects by using ultrasound measures. It is also important to study effects in low exposure areas to assess eventual thresholds of effects.The MAPSS (Maternal Air Pollution in Southern Sweden) cohort consists of linked registry data for around 48,000 pregnancies from an ultrasound database, birth registry and exposure data based on residential addresses. Measures of air pollution exposure were obtained through dispersion modelling with input data from an emissions database (NOx) with high resolution (100-500 m grids). Air pollution effects were assessed with linear regressions for the following endpoints; biparietal diameter, femur length, abdominal diameter and estimated fetal weight measured in late pregnancy and birth weight and head circumference measured at birth.We estimated negative effects for NOx; in the adjusted analyses the decrease of abdominal diameter and femur length were −0.10 (−0.17, −0.03) and −0.13 (−0.17, −0.01) mm, respectively, per 10 µg/m3 increment of NOx. We also estimated an effect of NOx-exposures on birth weight by reducing birth weight by 9 g per 10 µg/m3 increment of NOx.We estimated small but statistically significant effects of air pollution on late fetal and birth size and reduced fetal growth late in pregnancy in a geographic area with levels below current WHO air quality guidelines.