Background There are few published studies evaluating the impact of perinatal residence change on infant outcomes and whether these associations differ by socioeconomic status.

Methods We conducted a population-based cohort study using Washington State birth certificate data from 2007 to 2014 to assess whether women who moved during the first trimester of pregnancy (n=28 011) had a higher risk of low birth weight, preterm birth and small for gestational age than women who did not move during the first trimester (n=112 367). ‘Non-first-trimester movers’ were frequency matched 4:1 to movers by year. We used generalised linear models to calculate risk ratios and risk differences adjusted for maternal age, race, marital status, parity, education, smoking, income and insurance payer for the birth. We also stratified analyses by variables related to socioeconomic status to see whether associations differed across socioeconomic strata.

Results Moving in the first trimester was associated with an increased risk of low birth weight (6.4% vs 4.5%, adjusted risk ratio 1.37 (95% CI 1.29 to 1.45)) and preterm birth (9.1% vs 6.4%, adjusted risk ratio 1.42 (95% CI 1.36 to 1.49)) and a slight increased risk of small for gestational age (9.8% vs 8.7%, adjusted risk ratio 1.09 (95% CI 1.00 to 1.09)). Residence change was associated with low birth weight and preterm birth in all socioeconomic strata.

Conclusion Moving during the first trimester of pregnancy may be a risk factor for adverse birth outcomes in US women. Healthcare providers may want to consider screening for plans to move and offering support.