Ambient climatic factors and term birthweight: A study of critical windows of exposure in the Republic of Cyprus

Background: Reduced birthweight is associated with adverse perinatal and long-term outcomes. A few studies examined the association between climatic factors and birthweight with inconsistent results probably due to differences in exposure assessment, statistical models, climatic parameters, and study populations.

Methods: We obtained data from the Republic of Cyprus birth registry from 2007 to 2020, and matched climatic exposures (i.e., temperature, relative humidity, temperature variability, humidity variability) by the hospital district at birth. We used distributed lag models to examine the association between term birthweight, temperature, humidity, and their variability to identify critical windows. Our models were adjusted for coarse particulate matter level (≤10 μm [PM₁₀), and individual-level covariates. Subgroup analysis was conducted to examine effect modification by maternal age and education.

Results: We identified two critical windows of exposure to ambient temperature at early and late pregnancy. The cumulative change of birthweight per 5 °C increases in mean weekly temperature was -57.27 (2%) (95% Confidence Interval [CI]: 99.62 (3.1%), -14.92 (0.5%)) and -79.2 (2.5%) (95%CI: 117.03 (3.5%), -41.52 (1.3%)) grams during weeks 1-8 and weeks 28-37, respectively. There was no significant effect of humidity, temperature variability, or humidity variability on birthweight. Based on subgroup analysis, mothers with post-secondary education were more sensitive to temperature, but the marginal significance of differences in effect estimates may be linked with differences in sample size.

Conclusion: Our study suggests that higher ambient temperature exposure during early and late pregnancy is associated with lower birthweight in main and subgroup analysis. The findings demonstrate in a country highly impacted by climate change like Cyprus that rising temperatures may be associated with perinatal outcomes in susceptible populations during sensitive windows of exposure.