Particulate air pollution, fetal growth and gestational length: The influence of residential mobility in pregnancy

Abstract

Background: It remains unclear as to whether neglecting residential mobility during pregnancy introduces bias in studies investigating air pollution and adverse perinatal outcomes, as most studies assess exposure based on residence at birth. The aim of this study was to ascertain whether such bias can be observed in a study on the effects of PM10 on risk of preterm birth and fetal growth restriction.

Methods: This was a retrospective study using four pregnancy cohorts of women recruited in Connecticut, USA (N=10,025). We ascertained associations with PM10 exposure calculated using first recorded maternal address, last recorded address, and full address histories. We used a discrete time-to-event model for preterm birth, and logistic regression to investigate associations with small for gestational age (SGA) and term low birth weight (LBW).

Results: Pregnant women tended to move to areas with lower levels of PM10. For all outcomes, there was negligible difference between effect sizes corresponding to exposures calculated with first, last and full address histories. For LBW, associations were observed for exposure in second trimester (OR 1.09; 95% CI: 1.04-1.14 per 1μg/m(3) PM10) and whole pregnancy (OR 1.08; 95% CI: 1.02-1.14). For SGA, associations were observed for elevated exposure in second trimester (OR 1.02; 95% CI: 1.00-1.04) and whole pregnancy (OR 1.03; 95% CI: 1.01-1.05). There was insufficient evidence for association with preterm birth.

Conclusion: PM10 was associated with both SGA and term LBW. However, there was negligible benefit in accounting for residential mobility in pregnancy in this study.

Keywords: Exposure misclassification; Fetal growth; Pregnancy; Preterm birth; Residential mobility.

Figure 1

Adjusted log odds ratios for term LBW for a 1 μg.m⁻³ increase in PM₁₀ in each trimester (T1, T2, T3) and whole pregnancy (P) ascertained with first address, last address and updated histories. Results presented for each buffer distance (20km, 40km, 100km) and method of exposure assessment (closest monitor, inverse distance weighted).

Figure 2

Adjusted log odds ratios for SGA for a 1 μg.m⁻³ increase in PM₁₀ in each trimester (T1, T2, T3) and whole pregnancy (P) ascertained with first address, last address and updated histories. Results presented for each buffer distance (20km, 40km, 100km) and method of exposure assessment (closest monitor, inverse distance weighted).

Figure 3

Adjusted log hazard odds ratios for PTB for a 1 μg.m⁻³ increase in PM₁₀ in each trimester (T1, T2, T3), whole pregnancy (P), week of birth (lag 0) and the 6-week period prior to birth (lag 05). Exposure was ascertained with first address, last address and updated histories. Results presented for each buffer distance (20km, 40km, 100km) and method of exposure assessment (closest monitor, inverse distance weighted).

Figure 4

Adjusted log hazard odds ratios for PTB for a 1 μg.m⁻³ increase in PM₁₀ in each trimester (T1, T2, T3), whole pregnancy (P), week of birth (lag 0) and the6-week period prior to birth (lag 05). Exposure was ascertained with first address, last address and updated histories. Results presented for each buffer distance (20km, 40km, 100km) and method of exposure assessment (closest monitor, inverse distance weighted). Pregnancies were restricted to vaginal births.