Objectives Transportation noise has been associated with markers of obesity. We aimed to investigate whether road traffic and railway noise were associated with weight gain during and after pregnancy.

Methods Among the women participating in the Danish National Birth Cohort, 74 065 reported on weight before and during the pregnancy (gestational week 30) and 52 661 reported on weight before and 18 months after pregnancy. Residential address history from conception to 18 months after pregnancy was obtained in national registers, and road traffic and railway noise were modelled for all addresses. Associations between noise and gestational weight gain (GWG) and postpartum weight retention (PPWR) were analysed using the linear and log-binomial regression.

Results A 10 dB(A) higher road traffic noise was associated with an increase in GWG of 3.8 g/week (95% CI 2.3 to 5.3) and PPWR of 0.09 kg (95% CI 0.02 to 0.16). For PPWR, this association seemed confined to women who were overweight (0.17 kg, 95% CI 0.02 to 0.32) or obese (0.49 kg, 95% CI 0.26 to 0.73) before pregnancy. Further adjustment by nitrogen dioxide reduced GWG risk estimates and slightly increased PPWR risk estimates. Railway noise ≥65 dB(A) was associated with an increase in GWG of 4.5 g/week (95% CI −2.7 to 11.6) and PPWR of 0.26 kg (95% CI −0.09 to 0.60) compared with levels <55 dB(A).

Conclusions Our findings suggest that road traffic noise is associated with weight gain during and after the pregnancy, which adds to the literature linking transportation noise to adiposity.