Age and the Risk of Miscarriage

As women, we hear a lot about the difficulty of getting pregnant as we age, but staying pregnant can often be the bigger challenge, especially as our fertility begins to wane.

The risk of miscarriage rises as a woman ages, with a dramatic rise starting after age 37, with the steepest increase occurring after age 40. By age 45, less than 20% of all recognized pregnancies are viable.

The man’s age matters too. Having a partner over the age of 40 significantly raises the chances of a miscarriage.

Over half of miscarriages are caused by genetic abnormalities. As women age, chromosomal defects in their eggs become increasingly common. On average, a woman in her early 20s will have chromosomal abnormalities in about 17% of her eggs; this percentage jumps to nearly 80% by a woman’s early 40s. And as men age, chromosomal defects and point mutations–changes to a single nucleotide in their DNA–become increasingly common.

How The Chances of Miscarriage Vary By Age

Anne-Marie Nybo Anderson, of the Danish Epidemiology Science Centre, led the largest population-based study ever conducted on age and miscarriage. She tracked every  “reproductive outcome”–pregnancies, miscarriages, births, stillbirths, and induced abortions– from a total of over a million pregnancies.

The risk of pregnancy loss rose sharply by a woman’s late 30s and reached nearly 100% by age 45.

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Most of the rise in fetal losses came from an increase in miscarriage. However, rates of ectopic pregnancy also rise considerably with age:

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As do stillbirths:

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Somewhat reassuringly, while stillbirth risk increases after a woman’s late 30s, it remains less than 1% through age 45.

Anderson’s study’s findings are similar to another well-studied sample, that of U.S. pregnancies conceived via IVF:

CDC Data, 2010 ART cycles,
CDC Data, 2010, All Non-Donor IVF cycles in the U.S.

As you can see, the overall risk of miscarriage for IVF pregnancies in the US is slightly lower than that shown in the Denmark sample.

While IVF helps many couples overcome their fertility problems, it largely cannot overcome the age-related increase in genetic abnormalities. Without genetically normal sperm and eggs, a viable pregnancy is impossible.

The lower miscarriage rate is instead due to selection effects. The miscarriage rates are only from women who successfully manage to become pregnant through IVF, a select group. Not all women who undergo IVF have a successful egg retrieval. And of those eggs , not all will develop normally. The embryos ultimately transferred are chosen based on early signs of normal development, raising the odds of an ongoing pregnancy.

Men‘s Age and The Chances of Miscarriage

Most studies on miscarriage only consider the woman’s age on miscarriage, utterly ignoring any influence of her partner’s age.

This is not because of sexism. Instead, the reasons are largely practical: Women tend to marry men who are about their age, so it is hard to separate the risks of a woman’s age from the risks of her partner’s age; they are too confounded.

Despite this problem, several studies involving couples discordant for age now paint a clear and consistent picture: older prospective fathers raise the risk of miscarriage by about 25-50%. One study found an a 60% increase in the odds of a miscarriage if the father was over 40. Another found a roughly 25% increase in the risk of miscarriage for fathers over the age of 35.

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from Slama et al., 2005. Influence of Paternal Age on the Risk of Spontaneous Abortion. American Journal of Epidemiology

Other studies report similar effects; all finding that the risk rises most markedly for men over 40 (see here and here).

Men and Women’s Combined Age

Having a young partner may offset some of the risk associated with being older, for both men and women. Men whose partners are young, under 30, appear to have relatively low chances of miscarriage regardless of their own age, according to a large retrospective European study.

For women, though, having a young partner does not erase the effect of their own age. Women over 35 with relatively young partners, under 40, faced double to triple the odds of miscarriage compared to women under 30.

For women in their 30s,  having a younger partner lowers the chances of a miscarriage. Compared to a women in her early 30s with a partner of the same age or younger, a woman in her early 30 with a partner over 40 has roughly triple odds of a miscarriage. A woman over 35 with a partner over 40 has four times the odds of miscarriage.

Risk of Miscarriage After Confirmation of a Fetal Heartbeat

On a more positive note, women in their late 30s and early 40s have a good chance of a continuing pregnancy once a fetal heartbeat has been confirmed.

After confirmation of a heartbeat at 7-10 weeks, the risk of a subsequent miscarriage for women over 40 drops to about 10%. After 20 weeks, the risk of a pregnancy loss is less than 1%.

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The Bottom Line

The risk of miscarriage rises substantially with age, especially after age 40, for both men and women. Couples may suffer from the compound effect of their ages. Once a pregnancy is past the first trimester, however, the odds of a miscarriage are low, even for older couples.

Author: Amy Kiefer

As a former research scientist and proud mama of three little munchkins, I love digging into the research on all things baby-related and sharing it with my readers.

10 thoughts on “Age and the Risk of Miscarriage”

  1. Thanks for the information – great site altogether, and much needed!

    In this post, and in general in the studies you read and report, are weeks reported from LMP or from presumed date of conception?

  2. Amy- As someone about to start trying for number 2 at 39, I’m curious if these statistics are for age at time of conception or due date. Thanks!

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