Preterm birth during an extreme weather event in Québec, Canada: a "natural experiment".

To clarify the relationship between preterm birth (PTB) and extreme weather events, we evaluated PTB during a January 1998 ice storm that had led to a provincial emergency in the middle of winter in the province of Québec, Canada. Singleton live births for three periods (1993-1997, 1998, 1999-2003) were obtained (N = 855,320). PTB was defined as gestational age <37 completed weeks.