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Miscarriage Risks

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Miscarriage refers to the loss of pregnancy that occurs during the first 20 weeks of pregnancy. Miscarriage is more common than many women may think. Approximately one out of every five pregnancies ends in a miscarriage.

After suffering a miscarriage, many women wonder if their actions were responsible for causing it. There are a number of miscarriage risk factors that may make some women more likely to experience pregnancy loss. However, it is important to remember that the majority of miscarriage is caused by chromosomal abnormalities of the fetus.


Older women who conceive are more likely than younger women to experience a miscarriage, since they are more likely to conceive embryos with chromosomal abnormalities. Women under the age of 35 have about a 15 percent chance of a miscarriage and women between 35 and 45 have a 20 to 35 percent chance of miscarriage. Women over the age of 45 have around a 50 percent chance of miscarriage.

Lifestyle Factors

There are certain lifestyle factors that may make you more likely to suffer a miscarriage. One lifestyle habit that can contribute to a miscarriage is alcohol. Drinking three or more alcoholic drinks per week is associated with a higher rate of miscarriage.

Smoking cigarettes is associated with both infertility and miscarriage of pregnancies. According to the American Society for Reproductive Medicine (ASRM), female smokers who are using IVF have higher rates of miscarriage. The effects of smoking are also more pronounced in older patients.

Consuming caffeine during pregnancy is also related to miscarriage, especially in early trimester pregnancies. A 2008 study by the Kaiser Permanente Division of Research found that women who consumed 200 mg or more caffeine each day (two or more cups of regular coffee) were twice as likely to have a miscarriage as women who consumed no caffeine. Women who consumed less than 200 mg of caffeine a day had a 40 percent increased risk.

Previous Miscarriage

Having two or more miscarriages places women at a slightly greater risk of having another miscarriage. Studies from large samples of pregnant women show that if a woman has had two miscarriages, her chance of having a third is 20 percent. For women who have had four previous miscarriages, her chance of having a fifth is 40 percent.

Thrombophilia and Miscarriage

Thrombophilia is a disorder that involves a genetic predisposition to form harmful blood clots, which can lead to stroke or heart attack. Thrombophilia can cause clotting of blood vessels in the placenta, which makes it difficult or impossible for the fetus to receive an adequate blood supply. This can result in a miscarriage.

Thrombophilia most commonly causes miscarriage in the second and third trimesters of pregnancy, and rarely cause miscarriage in the first 10 weeks of gestation.

Uterine Abnormalities

Abnormalities of the uterus cause about 10 to 15 percent of recurrent miscarriages. These uterine abnormalities include an abnormally shaped uterus or divided uterus, uterine fibroids, or uterine scars. Uterine abnormalities can cause miscarriage by limiting the growth of the fetus or restricting its blood flow. Women with fibroids that may be affecting their fertility can receive a treatment called a myomectomy, which removes the fibroids but preserves the uterus.

Other Risk Factors

Other risk factors that may be related to miscarriage include exposure to toxins (radiation, lead, mercury, cleaning solvents, and pesticides), poorly controlled diabetes, obesity, hormonal problems, certain infections, and certain invasive tests.


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