Miscarriage risk by age, and what those numbers count
Ten percent at the lowest, rising steeply after 30. The denominator matters.
Every pregnancy from 2009 to 2013 in Norway, 421,201 in all, linked across three national registers:
| Mother's age | Risk of miscarriage |
|---|---|
| 25 to 29 | 10%, the lowest point |
| 45 and over | 53% |
The risk rose rapidly after age 30. Having had a previous miscarriage also raised the risk, and the more there had been, the higher it went: one prior loss gave an age-adjusted odds ratio of 1.54, two gave 2.21, three gave 3.97.
An older Danish study covering 1978 to 1992 reported much higher figures at the top of the range, 74.7% at age 45 and over. The two are not reconcilable as a single number. The Danish study counted losses that led to hospital admission, in an era of much less early pregnancy testing, and used a different denominator. This guide leads with the Norwegian figures because they are recent and the ascertainment is more complete, and it declines to present 74.7% as "the" risk at 45.
Miscarriage after a positive test is common at every age. It is also, for most women, followed by a successful pregnancy. Neither of those facts makes it a small event, and nobody should tell you it is.