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Up to 1 in 4 known pregnancies may end in miscarriage

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Among women who know they are pregnant, up to 25 percent of those pregnancies will end in a miscarriage, according to the National Library of Medicine.

That percentage is at the top of the institution’s estimated number of knowingly pregnant women who will have a miscarriage (10 to 25 percent), but health experts say the total number of miscarriages is probably much higher because many — perhaps most — miscarriages occur early in pregnancy, usually before a person knows they are pregnant.

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As many as 50 percent of all pregnancies may end in miscarriage, according to the March of Dimes, an Arlington, Va.-based nonprofit group focused on improving the health of mothers and babies. The term “miscarriage” refers to the unexpected loss of a fetus before the 20th week of pregnancy and is considered a naturally occurring event. From the 20th week on, loss of the baby is identified as a stillbirth. Most miscarriages occur because the fetus is not developing normally. This can be the result of the fetus having too many or too few chromosomes, which are the cell structures that hold genes, the National Institutes of Health says.

Chromosomal abnormality is usually a chance occurrence, happening as the embryo divides and grows, rather than something that is passed from parent to child through genetics. About 50 percent of miscarriages are linked to extra or missing chromosomes, according to the Mayo Clinic.

Other possible contributing factors include such things as drug or alcohol abuse, exposure to environmental toxins, uncontrolled diabetes and smoking. But health-care providers often cannot determine what caused a miscarriage. The risk of having a miscarriage, however, increases with a woman’s age, becoming highest after age 40.

This article is part of The Post’s “Big Number” series, which takes a brief look at the statistical aspect of health issues. Additional information and relevant research are available through the hyperlinks.

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