Miscarriage, technically called spontaneous abortion, is defined as the loss of a pregnancy before 20 weeks of gestation. It has been estimated to occur in up to 20 percent of all pregnancies. The actual number, however, is probably higher. Many miscarriages occur very early, going unnoticed before a woman is even aware that she is pregnant.
More than 80 percent of miscarriages occur in the first 12 weeks of pregnancy. At least half of these early miscarriages are thought to be caused by abnormalities with the fetus's chromosomes. Most of the time, the chromosome problems that cause a miscarriage are not inherited from the parents. In other words, the chromosome defect in the fetus is not caused by a similar defect in the chromosomes of the mother or father. Rather, these errors usually happen by chance as the fertilized egg begins to divide. The fetus would not have been able to survive when a miscarriage occurs due to a chromosome defect. Miscarriage early in pregnancy can occur as many as several weeks after the embryo or fetus has actually died.
The mother's health may be another cause of miscarriage. These usually occurs later in pregnancy. They include infection, chronic diseases such as diabetes or high blood pressure, and problems with the immune system. Abnormalities of the uterus or cervix can also cause miscarriage. Among these problems are cervical incompetence, in which the cervix begins to dilate too early in pregnancy. This type of miscarriage almost always happens in the second trimester.
Recurrent or repeated miscarriage is defined as three or more miscarriages in a row. (You may hear this referred to as habitual abortion.) The causes of this are much the same as those for a single miscarriage. Although tests can be done to find the reason for repeated miscarriage, the tests can be costly and the treatment options are somewhat limited. Even so, many couples go on to have a successful pregnancy later.
Miscarriage is not caused by exercising, having sex, working, or lifting heavy objects. Nausea and vomiting in early pregnancy, even if severe, will not cause a miscarriage. (In fact, there is some evidence that women who have these symptoms are less likely to miscarry.) Finally, it is unlikely that a fall, a blow, or a sudden fright can cause miscarriage.
One of the first signs of miscarriage is vaginal bleeding. Up to 25 percent of all pregnant women have bleeding at some point in pregnancy, about half of those will have a miscarriage. Bleeding that is a sign of miscarriage may be scant or heavy. It may be constant, or it may come and go. Bleeding may be followed by cramping abdominal pain and, in some women, lower backache. Although there may be other reasons for these symptoms (see "Spotting or bleeding" and "Pelvic pain"), you should contact your doctor if you have any type of bleeding or severe pain in pregnancy.
If you come to your doctor's office with bleeding, the first thing she or he will want to do is to perform a pelvic exam to check whether your cervix has begun to dilate. If it has, this situation is called threatened abortion; a miscarriage will not necessarily happen, but there is a chance that it might. Your doctor will also check whether the membranes surrounding the fetus have ruptured. If they have, and your cervix is dilated, then a miscarriage is certain.
If you have passed tissue, your doctor may suspect that a miscarriage has already occurred. If the tissue is available, he or she may be able to examine it to see whether it contains any fetal tissue or is actually a clot or a piece of placenta. An ultrasound exam is often used to try to determine whether there is a live fetus inside the uterus. With this test, your doctor will try to see the sac that surrounds the fetus or, using a special kind of ultrasonography, check the fetal heartbeat. If the fetus is not alive but has not been passed out of your body, this is called a missed abortion.
In cases of threatened abortion, bed rest and pain medication may be prescribed until the bleeding or pain has passed. If bleeding or pain is severe, you may need to be hospitalized. When the fetal membranes have broken, a miscarriage often occurs soon afterward. If it doesn't, however, and there is continued bleeding, pain, or a fever, the mother is at risk for developing a serious infection.
Because of this, the fetal tissue must be removed from the uterus. In this procedure, which is done under anesthesia, the cervix is gradually dilated and the tissue is gently scraped or suctioned out. If you have had a miscarriage or a procedure to empty the uterus, call your doctor right away if you have signs of miscarriage such as heavy bleeding, fever, chills, or severe pain. These could be a sign of an infection.
Most women who have had a miscarriage go on to have successful pregnancies in the future. Women with repeated miscarriages (three or more in a row) have a 70 to 85 percent chance of carrying another pregnancy to term. It is usually advised, however, to wait awhile before becoming pregnant again. Your care provider will be able to give you advice as to when to attempt pregnancy after a miscarriage.