Canadian researchers looked at 300,000 births and summer temperatures for a period of 30 years.
They found the risk of early term birth at 37 to 38 weeks was 27% higher when temperatures reached 90 degrees or more for several days.
However, hot weather had little effect on the risk of pre-term births.
In other health news, teens who listen to music that mentions brand names of alcoholic beverages are more likely to drink and abuse alcohol.
Researchers calculated the average teenager hears eight alcohol brand name references each day in popular music.
But those who listened to the most of this type of music were over three times more likely to have tried drinking and twice as likely to have engaged in binge drinking.
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