Miscarriage and Its Associations

Stephen Brown, M.D.

Disclosures

Semin Reprod Med. 2008;26(5):391-400. 

In This Article

Maternal Age

Many studies have documented that one of the strongest and most consistent associations with miscarriage is that of maternal age. A Danish registry study that examined the outcomes of more than 1.2 million pregnancies provides a powerful illustration of the impact of maternal age (Figure 2).[1] The increase in risk that occurs between the ages of 25 and 40 years is nearly threefold and is therefore larger than almost any other known effect.

Figure 2.

Relationship between fetal loss and maternal age in a Danish study of ∼1.2 million pregnancies.

As is discussed below, the incidence of fetal aneuploidy increases with maternal age, and this explains most of the strong association between maternal age and miscarriage. However, even after correcting for chromosome abnormality, increased age per se is still associated with an increased incidence of loss. Roughly 10% of pregnancies in women 36 years and older end in miscarriages with normal karyotype compared with ∼3% in women under 30 years.[2,3] Although unproved, it seems likely that this is due to the age-related increase in the incidence of such problems as uterine fibroids, endocrine abnormalities, and so forth. Given the dramatic association between miscarriage and maternal age, it is imperative that this effect be rigorously accounted for in all studies that seek to reveal associations between miscarriage and other factors. In light of the increases in average maternal age that have occurred in developed countries over the past several decades, it is likely that old estimates of the general frequency of miscarriage, based on younger populations, need to be revised.

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