In these twins, the odds of small for gestational age increased by 68% (95% CI: 27–123) and 51% (95% CI: 18–95) for each 10 mg/m³ increment in PM10 or NO2 during the third trimester.
The corresponding estimates for PM10 and NO2 on birth weight showed a reduction of 40.2 g (95% CI: 69.0 to 11.3) and 27.3 g (95% CI: 52.9 to 1.7), respectively.
These estimates are considerable higher than previously reported estimates in term born singletons.
An European multi cohort study in singletons observed that a 10 mg/m³ increased PM10 and NO2 (10 mg/m³) concentration during third trimester correspond to a decrease of 6 g (95% CI: 15 to 2) and 3 g (95% CI: 7 to 2) in birth weight (Pedersen et al., 2013).