Associations between Ambient Air Temperature, Low Birth Weight and Small for Gestational Age in Term Newborns in Southern Israel

Abstract

Background: Relatively few studies have examined the association between extreme ambient air temperatures (Ta) and pregnancy outcomes. We investigated the association between Ta, term low birth weight (tLBW) and small for gestational age (SGA) in singleton term infants, using a decade (2004-2013) of regional hospital data in southern Israel.Methods: We linked all births in Soroka University Medical Center in the southern district of Israel and insured by Clalit Health Services with pregnancy Ta, estimated by a hybrid satellite-based spatio-temporally model. Analyses were adjusted for calendar month, year, maternal age, gravidity, parity, ethnicity, sex, poverty index and population density.Results: The study population included 56,141 newborns, with 1,716 (3.1%) cases of tLBW and 8,634 (15.4%) cases of SGA. The average and the median daily Ta across the entire pregnancy were 19.9 (range: 14.6-24.9) degrees centigrade. The lowest Ta quartile was associated with higher risk of tLBW (OR = 1.38, 95%CI 1.16-1.64) while the highest Ta quartile was not significantly associated with tLBW (OR = 1.12, 95%CI 0.96-1.32), in comparison to the two intermediate quartiles. In addition, the lowest Ta quartile was associated with significantly higher risk of SGA (OR = 1.18, 95%CI 1.09-1.28) while the highest quartile was associated with significantly lower risk of SGA (OR = 0.91, 95%CI 0.85-0.99). When examining associations among tLBW, SGA and trimester-specific Ta exposures, we found decreased risk of SGA with high Ta quartile during the 1st trimester (OR = 0.82, 95%CI 0.73-0.92), and increased risk for SGA with low Ta quartile during the 3rd trimester (OR = 1.17, 95%CI 1.05-1.31), while all other associations were not statistically significant.Conclusion: Ta is negatively associated with SGA in singleton term births, with increased risk in low Ta and decreased risk in high Ta.