Early pregnancy loss is so common that many obstetricians consider it a normal part of reproduction.
Indeed, 20 percent of all pregnancies end in miscarriage, defined as the spontaneous end of a pregnancy during the first or early second trimester. Most occur within the first 12 weeks and some happen so early—before a missed period—that a woman may never know she was pregnant or that she miscarried. About 15 to 20 percent of miscarriages occur in the second trimester. “The majority of the time a miscarriage is a random, isolated event and we can’t pinpoint a cause,” says Henry Lerner, MD, clinical professor of obstetrics and gynecology at Harvard Medical School. Some 20 to 40 percent of miscarriages are due to more tangible factors, such as infections, an abnormally shaped uterus, inadequate hormone production, immunologic problems, or environmental toxins. These miscarriages tend to occur later in the first trimester or in the second trimester.
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