A woman's age and previous pregnancy complications influence her odds of miscarriage, a new study says.
The findings suggest that miscarriage and other pregnancy complications share underlying causes that require further investigation, according to the researchers.
"More focused studies of these associations might lead to new insights," they wrote in the March 20 issue of the BMJ.
Miscarriage is a common problem, but it's difficult to estimate a woman's risk because of inconsistent data collection, according to researchers, led by Maria Magnus, of the Norwegian Institute of Public Health.
Norway is one of the few countries where miscarriage data has been consistently collected since 2008.
In this study, the researchers analyzed data on more than 421,000 pregnancies in Norway between 2009 and 2013.
The overall miscarriage rate was about 13 percent. Miscarriage was lowest among women aged 25 to 29 (10 percent). It rose rapidly after age 30, reaching 53 percent among women aged 45 and older.
The study also found that after one miscarriage, the risk of another increased by half. After two miscarriages, the risk doubled. After three consecutive miscarriages, the risk quadrupled.
Women with previous pregnancy complications such as preterm delivery, cesarean section or gestational diabetes also had a higher risk of miscarriage. Preeclampsia (abnormally high blood pressure) in the previous pregnancy was not associated with increased risk of miscarriage, the authors said in a journal news release.
Women who were small at birth also had an increased risk of miscarriage, according to the study.
However, because this is an observational study, it can't establish cause and effect.
The March of Dimes has more on miscarriage.