Operational Medicine Medical Education and Training

Abnormal Pregnancy

Miscarriage (Spontaneous Abortion)

Miscarriage is the layman's term for spontaneous abortion, an unexpected 1st trimester pregnancy loss.

Since the term "spontaneous abortion" may be misunderstood by laymen, the word "miscarriage" is sometimes substituted.

Unruptured Cornual Ectopic Pregnancy

Abnormal Pregnancy

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Loss of a pregnancy during the first 20 weeks of pregnancy, at a time that the fetus cannot survive. Such a loss may be involuntary (a "spontaneous" abortion), or it may be voluntary ("induced" or "elective" abortion).

Abortions are further categorized according to their degree of completion. These categories include:

  • Threatened

  • Inevitable

  • Incomplete

  • Complete

  • Septic

Such losses are common, occurring in about one out of every 6 pregnancies.

For the most part, these losses are unpredictable and unpreventable. About 2/3 are caused by chromosome abnormalities incompatible with life. About 30% are caused by placental malformations and are similarly not treatable. The remaining miscarriages are caused by miscellaneous factors but are not usually associated with:

  • Minor trauma

  • Intercourse

  • Medication

  • Too much activity

Following a miscarriage, the chance of having another miscarriage with the next pregnancy is about 1 in 6. Following two miscarriages in a row, the odds of having a miscarriage with the next pregnancy is still about 1 in 6. After three consecutive miscarriages, the risk of having a fourth is greater than 1 in 6, but not very much greater.

Threatened Abortion

A threatened abortion means the woman has experienced symptoms of bleeding or cramping.

At least one-third of all pregnant women will experience these symptoms. Half will go on to abort spontaneously. The other half will see the bleeding and cramping disappear and the remainder of the pregnancy will be normal. These women who go on to deliver their babies at full term can be reassured that the bleeding in the first trimester will have no effect on the baby and that you expect a full-term, normal, healthy baby.

Treatment of threatened abortion should be individualized. Many obstetricians recommend bedrest in some form for women with a threatened abortion. There is no scientific evidence that such treatment changes the outcome of the pregnancy in any way, although some women may feel better if they are at rest. Other obstetricians feel that being up and active is psychologically better for the patient and will not change the risk of later miscarriage. Among these active women, strenuous physical activity is usually restricted, as is intercourse.

In an operational setting, bedrest may prove very useful. While you are not changing the outcome of the pregnancy (abnormal chromosomes will remain abnormal despite increased maternal rest), you may effectively postpone the miscarriage until a safer time. (days to possibly a week or two)

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Operational Obstetrics & Gynecology
2nd Edition

Bureau of Medicine and Surgery
Department of the Navy


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