Academic journal article Environmental Health Perspectives

A Population-Based Case-Control Study of Extreme Summer Temperature and Birth Defects

Academic journal article Environmental Health Perspectives

A Population-Based Case-Control Study of Extreme Summer Temperature and Birth Defects

Article excerpt

BACKGROUND: Although hyperthermia is a recognized animal teratogen and maternal fever has been associated with birth defects in humans, data on the relationship between high environmental temperatures and birth defects are limited.

OBJECTIVE: To determine whether pregnancies are potentially vulnerable to the weather extremes anticipated with climate change, we evaluated the relationship between extreme summer temperature and the occurrence of birth defects.

METHODS: We performed a population-based case-control study by linking the New York State Congenital Malformations Registry to birth certificates for the years 1992-2006. We selected nonmalformed infants from a 10% random sample of live births as controls. We assigned meteorologic data based on maternal residence at birth, summarized universal apparent temperature (UAT; degrees Fahrenheit) across the critical period of embryogenesis, and estimated adjusted odds ratios (aOR) and 95% confidence intervals (CI) with multivariable logistic regression, controlling for confounders available on the birth certificate.

RESULTS: Among 6,422 cases and 59,328 controls that shared at least 1 week of the critical period in summer, a 5-degree increase in mean daily minimum UAT was significantly associated with congenital cataracts (aOR = 1.51; 95% CI: 1.14, 1.99). Congenital cataracts were significantly associated with all ambient temperature indicators as well: heat wave, number of heat waves, and number of days above the 90th percentile. Inconsistent associations with a subset of temperature indicators were observed for renal agenesis/hypoplasia (positive) and anophthalmia/microphthalmia and gastroschisis (negative).

CONCLUSIONS: We found positive and consistent associations between multiple heat indicators during the relevant developmental window and congenital cataracts which should be confirmed with other data sources.

KEY WORDS: birth defects, climate change, congenital cataracts, heat, temperature. Environ Health Perspect 120:1443-1449 (2012). [Online 27 June 2012]

Hyperthermia is a well-known animal teratogen, and maternal fever has been associated with birth defects in human studies (Edwards 2006; Edwards et al. 1995; Graham 2005; Graham et al. 1998; Warkany 1986). In all species, the teratogenic effect of the hyperthermic insult depends on timing, intensity, and duration of exposure, and the central nervous system appears to be most vulnerable. Most anomalies detected in animal studies have been observed in clinical and epidemiologic studies of maternal fever and febrile illness, including neural-tube defects, microphthalmia, congenital cataracts, abdominal wall defects, congenital heart defects, microcephaly, limb defects, craniofacial malformations, and renal defects (Edwards 2006). In a meta-analysis of epidemiologic studies of maternal first trimester hyperthermia and neural-tube defects, a statistically significant overall odds ratio (OR) was reported (Moretti et al. 2005). Furthermore, associations with maternal fever were attenuated after adjustment for the use of antipyretics, suggesting that the fever was teratogenic and not the underlying illness (Czeizel et al. 2007; Hashmi et al. 2010; Oster et al. 2011; Vogt et al. 2005).

There is a paucity of data on the teratogenicity of external heat-generating sources or hot environments, which may increase maternal core temperature during pregnancy, and the exposure assessments for these studies are typically based on postpartum maternal interviews about environmental conditions during early pregnancy. Existing data support a possible association of neural-tube defects with hot tub and sauna use during early pregnancy (Chambers 2006; Suarez et al. 2004), but not with hot environments (Suarez et al. 2004). In studies of congenital heart defects, no associations were observed for hot tub, bath, or sauna use or exposures to hot environments in early pregnancy (Judge et al. …

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