Women who gain weight during a first pregnancy and then do not take it off prior to their second pregnancy may be at higher risk even if they are still within a normal weight range when they become pregnant for the second time, the researchers report.

Doctors from the Harvard School of Public Health and the Karolinska Institute in Stockholm collaborated on the study.

It is still unknown whether the extra weight itself causes the increased pregnancy risk. The root cause might be some other factor contributing to both the added weight and the added risk.