A miscarriage (spontaneous abortion) is the loss of a fetus due to natural causes before 24 weeks of pregnancy.
Miscarriage is a common end to a high-risk pregnancy. A miscarriage occurs in about 15% of recognized pregnancies. Many more miscarriages may be unrecognized because they occur before women know they are pregnant. About 85% of miscarriages occur during the first 12 weeks of pregnancy. Most miscarriages that occur during this time are thought to occur because something was wrong with the fetus, such as a birth defect or a genetic disorder.
The remaining 15% of miscarriages occur during weeks 13 to 24. For about one third of these miscarriages, no cause is identified. The other two thirds of them result from problems in the women. A miscarriage may occur because women have structural abnormalities of the reproductive organs, such as a double uterus or an incompetent cervix, which tends to open (dilate) as the uterus enlarges. A miscarriage can also occur if women use cocaine, are injured, or have certain disorders. These disorders include an underactive thyroid gland (hypothyroidism), diabetes, infections (such as a cytomegalovirus infection or rubella), and connective tissue disorders (such as lupus). Rh incompatibility (when a pregnant woman has Rh-negative blood and the fetus has Rh-positive blood) also increases risk. Emotional disturbances in women are not linked with miscarriages.
A miscarriage is more likely for women who have had a miscarriage or preterm labor in a previous pregnancy. For women who have had three consecutive miscarriages during the 1st trimester, the chance of having another miscarriage is about 1 in 4. Before trying to become pregnant again, women who have had repeated miscarriages may want to be checked for genetic or structural abnormalities and for other disorders that increase the risk of a miscarriage. An imaging procedure (such as hysteroscopy, hysterosalpingography, or ultrasonography) may be performed to look for structural abnormalities. If the cause of a previous miscarriage is identified, treatment may correct the problem.
A miscarriage is usually preceded by spotting or more obvious bleeding and a discharge from the vagina. The uterus contracts, causing cramps. About 20 to 30% of pregnant women have some bleeding or cramping at least once during the first 20 weeks of pregnancy. About half of these episodes result in a miscarriage.
Early in a pregnancy, the only sign of a miscarriage may be a small amount of vaginal bleeding. Later in a pregnancy, a miscarriage may cause profuse bleeding, and the blood may contain mucus or clots. Cramps become more severe until eventually, the uterus contracts enough to expel the fetus and placenta.
Sometimes the fetus dies but no miscarriage occurs. In such cases, the uterus does not enlarge. Rarely, the dead tissues in the uterus become infected before, during, or after a miscarriage. Such an infection may be serious, causing fever, chills, and a rapid heart rate. Affected women may become delirious, and blood pressure may fall.
Diagnosis and Treatment
If a pregnant woman has bleeding and cramping during the first 20 weeks of pregnancy, a doctor examines her to determine whether a miscarriage is likely. The doctor examines the cervix to determine whether it is dilating. If it is not, the pregnancy may be able to continue. If it is dilating, a miscarriage is more likely.
Ultrasonography is usually also performed. It may be used to determine whether a miscarriage has already occurred or, if not, whether the fetus is still alive. If a miscarriage has occurred, ultrasonography can show whether the fetus and the placenta have been expelled.
If the fetus is alive and a miscarriage seems likely, bed rest is advised to help reduce bleeding and cramping. If possible, the woman should not work but should stay off her feet at home. Refraining from sexual intercourse is advised, although intercourse has not been definitely connected with miscarriages.
If a miscarriage has occurred and the fetus and the placenta have been expelled, no treatment is needed. If some of these tissues remain in the uterus, suction curettage is performed to remove them.
If the fetus dies but remains in the uterus, suction curettage is usually used to remove the fetus and the placenta. If the fetus dies late in the pregnancy, a drug that can induce labor may be given intravenously instead. Oxytocin stimulates the uterus to contract and expel the fetus. Afterward, curettage may be needed to remove pieces of the placenta.
After a miscarriage, women may feel grief, sadness, anger, guilt, or anxiety about subsequent pregnancies. Grief for a loss is a natural response and should not be suppressed or denied. Talking about their feelings with another person may help women deal with their feelings and gain perspective. Women who have had a miscarriage may wish to talk with their doctor about the likelihood of a miscarriage in subsequent pregnancies. Although having a miscarriage increases the risk of having another one, most women who have a miscarriage do not have problems in subsequent pregnancies.