London - Heatwaves could cause women to go into labour early, according to researchers.
They found the risk of an early birth soars by 27 percent when temperatures rise over 32degC for between four and seven days.
The researchers looked at data from 300 000 births that took place in Montreal between 1981 to 2010 against summer temperatures recorded during this period.
Overall they found that extreme heat did not seem to increase the number of early births, defined as less than 37 weeks.
However, in women who were 37 or 38 weeks pregnant, with around two weeks to go until they reached full term, the risk of an early delivery increased by 17 percent following three days of 32C or more.
When the heat lasted for four to seven days, the risk went up to 27 percent.
Studies have shown that children born at 37 or 38 weeks suffer more respiratory problems, while early-term newborns are also at greater risk of death.
Lead author Dr Nathalie Auger, of the University of Montreal, said: “Small-scale studies suggest that heat-induced stress increases uterine contractility. We also suspect that dehydration reduces blood supply to the uterus, increasing the release of pituitary hormones that induce labour.” - Daily Mail