Narrator:    This is Science Today. Infants born more than one week past their due dates have a higher risk of both impaired health and death. Dr. Andrew Caughey, an obstetrician at the University of California, San Francisco, conducted two studies along with the University of California, Berkeley that focused on the risk of pregnancies progressing beyond 41 weeks of gestation. In the first study, the researchers focused on the risk of infant death for babies born at 41 and 42 weeks.

Caughey:    We found that if they baby was born at 41 or 42 weeks of gestational age, the probability of neo-natal death was higher than if you've delivered at 38, 39 or 40 weeks of gestational age.

Narrator:    In a second study, the researchers found that the risk of cesarean deliveries and poor health outcomes for both mom and baby increased as early as 40 weeks.

Caughey:    In pregnancy, it does appear that there's an optimal time and that optimal time is right around that due date for the average patient. So, we think it's somewhere in the 39 to 40 week gestational age for the average patient.

Narrator:    For Science Today, I'm Larissa Branin.