Maternal Periconceptional Exposure to Extreme Ambient Heat and Risk of Neural Tube Defects in the Offspring in Georgia, 1994-2017 Open Access
Beagle, Lauren (Spring 2023)
Abstract
Background: Rising global temperatures have been associated with various health outcomes, including birth defects. Neural tube defects are the second most common type of birth defect in the US, and there has been limited, conflicting research on how maternal exposure to extreme ambient heat in early pregnancy may impact their occurrence. There is an increasing need to understand population health impacts of extreme ambient temperature exposure to guide recommendations and policy.
Methods: We conducted a case-control study using fetal death and birth records in Georgia from 1994-2017. All cases of neural tube defects, specifically anencephaly and spina bifida, were included and matched 4:1 to controls (pregnancies without birth defects) based on maternal county of residence and birth year. Daily county-level ambient temperature data from 2 weeks prior to 6 weeks post-last menstrual period were linked to birth certificate data by county of residence. Four heatwave metrics (2 categorical, 2 dichotomous) were created using different combinations of the duration and intensity of hot days (based on daily apparent temperature exceeding the county-specific 95th percentile). Data were analyzed using conditional logistic regression, adjusting for possible confounders as identified by previous literature.
Results: The study consisted of 673 cases (343 anencephaly, 330 spina bifida) and 2,692 controls. Overall, there was a positive association with maternal exposure to an increasing number of extreme heat days and consecutive extreme heat days during both pre- and post-conception and odds of the offspring developing a neural tube defect. During the defined exposure window, the adjusted odds ratios for neural tube defects were 1.40 (95% CI 1.11, 1.77) for mothers with 13+ days of extreme heat exposure compared to women with no days of extreme heat exposure and 1.36 (1.09, 1.70) for women with 6+ consecutive extreme heat days compared no days of extreme heat exposure.
Conclusion: This study provides epidemiological evidence demonstrating a modest positive association between periconception extreme heat exposure and risk of neural tube defects. Further studies should examine this association, considering individual-level exposures and the role of other possible effect modifiers that were not available in this study, such as folic acid supplement intake.
Table of Contents
Introduction………………………………………………….…………………………………….1
Methods……………………………………………………………………………….…………...3
Results………………………………………………………………………………….………….5
Discussion…………………………………………………………………………….…………...7
Conclusion…………………………………………………………………….……………...….13
Figures………………………………………………………………………………….………..14
Table 1. Distribution of demographic characteristics between infants with any neural
tube defect, anencephaly or spina bifida and matched controls in Georgia, USA (1994–2017) …………………………………………………………………………………….14
Table 2. Association of exposure to extreme heat of varying durations during
preconception and post conception to risk of neural tube defects (combined and by specific type) in Georgia, USA (1994-2017) ……………………………………………16
Table 3. Association of exposure to extreme heat of varying durations during
preconception and post conception to neural tube defects (combined and by specific type) in Georgia, USA solely following the mandatory folic acid fortification policy of staple grain products (1998-2017) ……………………………………………………………...19
References………………………………………….…………………………………………….22
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