Researchers examined 56 million births from 1969 to 1988 and correlated that data to weather data in the areas where the births occurred. They found a spike in deliveries on days where the mercury topped 90 degrees Fahrenheit.  “That rise, then fall, indicates a forward shift or an acceleration of deliveries and ultimately a loss of up to two weeks gestation for those births,” said study author Alan Barreca, an associate professor in environmental economics at the University of California, Los Angeles.