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Threatened Miscarriage

Threatened Miscarriage Overview

Any bleeding other than spotting during early pregnancy is considered a threatened miscarriage. (A miscarriage may also be referred to as a spontaneous abortion.) Vaginal bleeding is common in early pregnancy. About one of every four pregnant women has some bleeding during the first few months. About half of these women stop bleeding and have a normal pregnancy.

The bleeding and pain associated with threatened miscarriage are usually mild. In the best case, the cervical os (mouth of the womb) is closed. (A health care professional can determine if the cervical os is open by performing a pelvic exam.) Typically, no tissue has been passed from the womb. The womb and Fallopian tubes may be tender.

When a miscarriage is inevitable, the cervical os is open (dilated). Bleeding is often heavier, and abdominal pain and cramping often occur.

If a miscarriage is incomplete, the cervical os is open, and the pregnancy is being expelled. Ultrasound reveals some material that remains in the womb. Bleeding is heavy and abdominal pain is almost always present.

With a complete miscarriage, bleeding and abdominal pain have occurred but have usually stopped. Products of conception have been passed. The early fetus has been passed and was not alive. Ultrasound reveals an empty womb.

Threatened Miscarriage Causes

Although the actual cause of the miscarriage is frequently unclear, the most common reasons include the following:

  • An abnormal fetus is almost always the cause of miscarriages during the first 3 months of pregnancy (first trimester). Problems in the chromosomes cause an abnormal fetus and are found in more than half of miscarried fetuses. The risk of defective chromosomes increases with the woman's age.
  • Miscarriage during the fourth through sixth months of pregnancy (second trimester) is usually related to an abnormality in the mother rather than in the fetus.
    • Chronic illnesses, including diabetes, severe high blood pressure, kidney disease, lupus, and underactive or overactive thyroid gland, are frequent causes of a miscarriage. Prenatal care is important because it screens for some of these diseases.
    • Inadequate hormone production is an occasional cause of miscarriages.
    • Acute infections, including German measles, CMV (cytomegalovirus), mycoplasma (atypical pneumonia) and other unusual germs can also cause miscarriage.
    • Diseases and abnormalities of the internal female organs can also cause miscarriage. Some examples are an abnormal womb, fibroids, weakness in the mouth of the womb (cervix), abnormal growth of the placenta (also called the afterbirth), and being pregnant with multiples.
    • Other factors, especially certain drugs, including excessive caffeine, alcohol, tobacco, and cocaine, may be the cause.
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