Background
Few studies have examined maternal modifiers of temperature and adverse birth outcomes because of lack of data. We assessed the relationship between apparent temperature, preterm delivery (PTD) and maternal demographics, medical conditions, and behaviors.
Methods
A time-stratified case-crossover analysis was conducted using for 14,466 women who had a PTD (20 to less than 37 gestational weeks) from 1995 to 2009 using medical records from a large health maintenance organization in Northern California. Effect modifiers considered by stratification included several maternal factors: age, race/ethnicity, depression, hypertension, diabetes, smoking, alcohol use, pre-pregnancy body mass index, and Medicaid status. Difference by infant sex were also considered. Apparent temperature data for women who had a monitor located within 20 kilometers of their residential zip codes were included. All analyses were stratified by warm (May 1 through October 31) and cold (November 1 through April 30) seasons.
Results
Every 10°F (5.6°C) increase in average cumulatively weekly apparent temperature (lag06), a greater risk was observed for births occurring during the warm season (11.63%; 95% CI: 4.08, 19.72%) compared to the cold season (6.18%; −2.96, 16.18%), especially for mothers who were younger, Black, Hispanic, underweight, had Medicaid prior to giving birth, or had pre-existing or gestational hypertension or diabetes.
Conclusions
Our findings suggest that warmer apparent temperatures may exacerbate the risk of PTD, particularly for subgroups of women at higher risk.