Findings point to new insights into possible shared underlying causes of miscarriage
The risk of miscarriage varies greatly with a woman's age, shows a strong pattern of recurrence, and is increased after some pregnancy complications, finds a new study.
Miscarriage is a common pregnancy outcome, but the risk is challenging to estimate because of inconsistent recording
Norway is one of the few countries where miscarriage data has been consistently collected since 2008.
There were 421,201 pregnancies during the study period. After accounting for induced abortions, the overall miscarriage rate was 12.8%. The risk of miscarriage was lowest among women aged 25-29 (10%), and rose rapidly after age 30, reaching 53% among women age 45 years and over.
There was also a strong recurrence risk of miscarriage. After one miscarriage, the risk of another was increased by half, after two, the risk doubled, and after three consecutive miscarriages, the risk was four times greater
Previous pregnancy complications also predicted a higher risk of miscarriage. For example, if the previous birth ended in a preterm delivery, caesarean section, or if the woman had diabetes during pregnancy (gestational diabetes).
However, pre-eclampsia (abnormally high blood pressure) in the previous pregnancy was not associated with increased risk of miscarriage.
Women who themselves were born small also had an increased risk of miscarriage.
This is an observational study, and as such, can't establish cause, and the researchers point to some limitations, such as the possibility that early miscarriages which did not result in contact with specialist health-care services were not captured.