A threatened abortion is a condition that suggests a miscarriage might take place before the 20th week of pregnancy.

A small number of pregnant women have some vaginal bleeding, with or without abdominal cramps, during the first trimester of pregnancy. This is known as a threatened abortion. Most of these pregnancies go on to term with or without treatment. Spontaneous abortion occurs in just a small percentage of women who have vaginal bleeding during pregnancy.

When spontaneous abortion occurs, the usual cause is fetal death. Such death is typically the result of a chromosomal or developmental problem. Other possible causes include:

• Defects in the mother's anatomy
• Endocrine factors
• Immune system factors
• Infection
• Systemic disease in the mother

About half of all fertilized eggs abort on their own, usually before the woman knows she is pregnant. The rate of spontaneous abortion is very low among known pregnancies. These usually occur 7 - 12 weeks into the pregnancy.

Risks of threatened abortion are higher in:

• Women over age 35
• Women with a history of 3 or more spontaneous abortions
• Women with systemic disease (such as diabetes or thyroid dysfunction)

• Abdominal cramps with or without vaginal bleeding
• Vaginal bleeding during the first 20 weeks of pregnancy (last menstrual period was less than 20 weeks ago)

Note: With true miscarriage, low back pain or abdominal pain (dull to sharp, constant to intermittent) typically occurs and tissue or clot-like material may pass from the vagina.

Pelvic exam shows a cervix that isn't thinned (effaced) or open (dilated). Either of these can suggest that a miscarriage will soon occur.

Other tests include:

• Beta HCG (quantitative) test over a period of days or weeks to confirm whether the pregnancy is continuing or the fetus has died
• CBC to find out the amount of blood loss
• Serum HCG to confirm that the woman is pregnant
• Ultrasound to detect fetal heartbeat
• WBC with differential to rule out infection

This disease also can change the results of the serum progesterone test.