About 10-15% of women who get pregnant experience miscarriage at least once in their life. Many factors can cause miscarriage, but recent evidence suggests the role of maternal age and pregnancy history. The objective of this study is to evaluate the effects of maternal age and pregnancy history on miscarriage.

This is a prospective register-based study that included a total of 421,201 Norwegian women who were pregnant during 2009-13. The primary outcome of the study was the risk of miscarriage according to the age and pregnancy history of the women.

The risk of miscarriage was the lowest in women aged 25-29 (10%) and rose speedily after the age of 30. The risk of miscarriage in women aged 45 and over was 53%. The risk of miscarriage was also strongly associated with pregnancy history. The age-adjusted ratio of miscarriage was 1.54 after one miscarriage, 2.21 after two miscarriages, and 3.97 after three miscarriages. The risk of miscarriage was also high if the previous pregnancy ended up in preterm delivery (OR 1.22), stillbirth (1.30), and cesarean section (1.6). 

The research concluded that the risk of miscarriage was strongly associated with maternal age and pregnancy history. Pregnancy complications, like miscarriage, preterm delivery, or stillbirth, were linked with an increased risk of miscarriage.

Ref: https://www.bmj.com/content/364/bmj.l869