Women who wait less than 18 months between pregnancies may be more likely to deliver early.
A new study from the University of Cincinnati College of Medicine looked at the birth records of more than 400,000 babies.
Researchers found women who waited less than 18 months to get pregnant after having a child were less likely to make it to 39 weeks gestation.
Half of the women who waited less than a year delivered prematurely.
They also found rates of premature birth were higher among African American women.
Researchers say doctors should advise women to wait 18 months or more between pregnancies.