The impact of high apparent temperature on spontaneous preterm delivery: a case-crossover study

Abstract

BackgroundDespite the prediction that temperatures are expected to increase in the future, little is known about the health effects of increasing temperatures on pregnant women. The objective of this study was to investigate the impact of apparent temperature on spontaneous preterm delivery (PTD).MethodsA case-crossover study of 14,466 singleton spontaneous preterm deliveries occurring between January 1, 1995 and December 31, 2009 among Kaiser Permanente Northern California (KPNC) members was conducted. Preterm deliveries were identified through KPNC's Electronic Health Records (EHR) data. Data on gestational age at delivery, infant sex, and maternal address were also extracted from KPNC's EHR and linked to meteorologic and air pollution monitoring data based on residential zip code.ResultsAn 11.6% (95% CI: 4.1, 19.7) increase in spontaneous PTD was associated with a 10 °F (5.6 °C) increase in weekly average (lag06) apparent temperature, during the warm season. During the cold season, increases in apparent temperature did not significantly impact the overall effect of spontaneous PTD (6.2%, (95% CI: -3.0, 16.2) per 10 °F (5.6 °C) increase in weekly average (lag06) apparent temperature). Significant differences in the relationship between apparent temperature and spontaneous PTD emerged for region, gestational age and infant sex, during the cold season. No significant differences emerged for air pollutants.ConclusionsOur findings provide evidence for an increase in the odds of spontaneous PTD associated with increases in apparent temperature, especially during the warm season.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-017-0209-5) contains supplementary material, which is available to authorized users.

Regan et al. Reply to “Sibling Comparison Design in Birth-Spacing Studies”

“…This exclusion is analogous to case-crossover designs, which have proven to be valuable tools in further evaluating the potential impacts of other perinatal exposures. 8,9 In the absence of randomized trials, we agree with Hutcheon and Harper 6…”

First Trimester Maternal Vitamin D Status and Risks of Preterm Birth and Small-For-Gestational Age

“…We also included season at blood draw, skin color and ethnicity, since these were hypothesized to be strongly related to vitamin D status and there is increasing evidence of an association with perinatal outcome. Seasonal variations in respiratory and viral infections, as well as in the temperature, impact on preterm birth [37][38][39][40], while skin color is related to ethnicity, which has an independent effect on preterm birth and SGA; recent research suggests that skin tone may also be directly relevant to the investigation of perinatal outcomes [41][42][43].…”

Time series analysis of total and direct associations between high temperatures and preterm births in Detroit, Michigan

“…The strong association between short-term temperature exposure and PTB in Detroit, Michigan, USA was consistent with several other studies’ observed associations between PTB or diminished gestational age and temperature exposures within the week prior to delivery at regionally high temperatures. Regions in which these associations have been found include Central Australia (8.3% at 40°C daily maximum temperature),11 Northern California, USA (11.6% increase for a 5.6°C increase in weekly average AT in the warm season),34 Alabama, USA (32.4% increase with two consecutive days of daily mean temperatures above the 98 th percentile),39 Barcelona, Spain (5-day reduction in average gestational age with heat index above the 99 th percentile),8 Rome, Italy (1.9% increase per 1°C increase in maximum AT in the prior 2 days and 19% increase during heat waves),40 Brisbane, Australia (13% to 100% increase during heat waves), in an aggregated sample of 12 US cities (12% to 16% increase with 2.8°C increase in prior week),12 in Southern China (7% increase with previous-week temperatures above 95 th percentile)10 and in a multi-city USA sample (2% increased PTB risk with extreme heat in the prior 4 days) 41…”

“…Case-crossover analysis is commonly used in studies of PTB and temperature 12 13 34. Because PTB is not a rare event in this particular population, the case-crossover ORs would not approximate risk ratios.…”