Environment/Climate Change
Heat waves and preterm and early-term birth: effect modification by maternal- and area-level vulnerability factors Amy Fitch* Amy Fitch Mengjiao Huang Matthew J. Strickland Andrew J. Newman Joshua L. Warren Howard H. Chang Lyndsey Darrow
Background: Extreme heat events are increasing in frequency and intensity and they disproportionately affect vulnerable populations. Previous research suggests that maternal exposure to extreme heat in the days before delivery is associated with preterm and early-term birth.
Methods: We examined possible effect modification of the relationship between acute heat wave exposure and two birth outcomes: preterm (<37 weeks) and early-term (37-38 weeks). Effect modifiers explored include area-level factors (e.g., social deprivation index (SDI)) and individual-level factors (e.g., maternal education). Live, singleton preterm or early-term births were identified from state vital records in eight states (CA, FL, GA, KS, NC, NJ, NV, OR) from 1990 to 2017. A novel, urban heat island-focused dataset was linked to births by zip code. Daily mean temperatures were used to identify heat waves. Heat waves were defined in multiple ways according to intensity and duration. We conducted time-stratified case-crossover (conditional logistic regression) analyses, pooling effect estimates across states using a fixed effects meta-analysis.
Results: Preliminary pooled results from three states (CA, NV, OR) suggested effect modification by SDI for early-term birth. For example, ORs (95% CI) for 4-consecutive days over the local 97.5th percentile mean temperature are 1.038 (1.024, 1.052) for high SDI and 1.014 (0.989, 1.039) for low SDI. There is no evidence of effect modification for preterm birth, OR 1.023 (0.999, 1.058) for high SDI and 1.025 (0.979, 1.073) for low SDI. These results are consistent with estimates for other heat wave definitions we explored. Results including the five additional states and other possible effect modifiers will be presented.
Conclusion: Preliminary results suggest that the effect of acute heat wave exposure on early-term birth is stronger in economically-disadvantaged communities.