What is a miscarriage?
A miscarriage is the spontaneous loss of a pregnancy from conception to 20 weeks' gestation. The term stillbirth refers to the death of a fetus after 20 weeks' gestation. Miscarriage is sometimes referred to as spontaneous abortion, because the medical term abortion means the ending of a pregnancy, whether intentional or unintentional. Most miscarriages occur in the first trimester of pregnancy, from seven to twelve weeks after conception.
How common is miscarriage?
Miscarriage is very common. As many or even most miscarriages occur so early in pregnancy that a woman does not even realize that she is pregnant, it is difficult to estimate how frequently miscarriages occur. Some experts believe that about half of all fertilized eggs die before implantation or are miscarried. Of known pregnancies (in which a woman misses a period or has a positive pregnancy test), about 10% to 20% end in miscarriage.
What causes miscarriage?
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The majority of miscarriages are believed to be caused by genetic problems within the embryo that would prevent a baby from developing normally and surviving after birth. These fatal genetic errors are not usually related to genetic problems in the mother.
In other cases, certain illnesses or medical conditions can cause miscarriage or may increase the risk of miscarriage. Mothers who have diabetes or thyroid disease are at increased risk of miscarriage. Infections that spread to the placenta, including some viral infections, can also increase the risk of miscarriage.
In general, risk factors for miscarriage include the following:
- Older maternal age
- Cigarette smoking (>10 cigarettes/day)
- Moderate to high alcohol consumption
- Trauma to the uterus
- Radiation exposure
- Previous miscarriage
- Maternal weight extremes (BMI either below 18.5 or above 25 kg/m2)
- Anatomical abnormalities of the uterus
- Illicit drug use
- Use of nonsteroidal anti-inflammatory drugs (NSAIDs) around the time of conception may increase the risk of miscarriage
Women who had one miscarriage have an incidence of miscarriage of about 20%, whereas women who have three or more consecutive miscarriages may have a risk as high as 43%.
What are the types of miscarriage?
Miscarriages are sometimes referred to by tissue-specific names to reflect the clinical findings or the type of miscarriage. Examples include:
- Threatened abortion: a woman may experience vaginal bleeding or others signs of miscarriage (see below), but loss of the pregnancy has not yet occurred
- Incomplete abortion: some of the products of conception (fetal and placental tissues) have been expelled from the uterus, but some remain.
- Complete abortion: all of the tissue from the pregnancy has been expelled
- Missed abortion: the fetus has not developed, so there is no viable pregnancy, but there is placental tissue and/or fetal tissue contained within the uterus
- Septic abortion: a miscarriage in which there is infection in the presence of retained fetal and/or placental tissue.
What are signs and symptoms of a miscarriage?
Vaginal bleeding and pelvic pain are the hallmark symptoms of miscarriage. All vaginal bleeding during pregnancy should be investigated, although not all instances of bleeding result from a miscarriage. Bleeding in the first trimester of pregnancy is very common and does not typically signify a miscarriage. The pain tends to be dull and cramping, and it may come and go or be present constantly. Sometimes, there is passage of fetal or placental tissue. This material may appear whitish and covered with blood. The bleeding may be associated with the passage of blood clots. The amount of bleeding does not necessarily correlate with the severity of the situation, and miscarriage may be associated with bleeding that ranges from mild to severe.
How is miscarriage diagnosed?
An ultrasound examination is typically performed if a woman has symptoms of a miscarriage. The ultrasound can determine if the pregnancy is intact and if a fetal heartbeat is present. Ultrasound examination can also reveal whether the pregnancy is an ectopic pregnancy (located outside of the uterus, typically in the Fallopian tube), which may have similar symptoms and signs as miscarriage. Other tests that may be performed include blood tests for pregnancy hormones, blood counts to determine the degree of blood loss or to see whether infection is present, and a pelvic examination. The mother's blood type should also be checked at the time of a miscarriage, so that Rh-negative women can receive an injection of rho-D immune globulin (RhoGam) to prevent problems in future pregnancies.
What happens after a miscarriage?
There are no specific treatments that can stop a miscarriage, although women who are at risk and have not yet miscarried may be advised to rest in bed, abstain from sexual activity, and restrict all physical activity until any warning signs are no longer present. Once a miscarriage occurs, there is no treatment available. In many cases, the miscarriage will take its course, and unless there is severe pain and cramping or severe blood loss, no treatment is required. If a miscarriage does not completely clear the pregnancy tissue from the uterus, a procedure known as a dilatation and curettage (D&C) can be performed to remove the remaining pregnancy material. This treatment is used in the case of a missed abortion, for example, when the pregnancy material is not expelled from the uterus.
As mentioned above, women who are Rh-negative will receive a dose of rho-D immune globulin to prevent complications in future pregnancies.
If a miscarriage is due to infection, antibiotic treatment will be given.
Miscarriage is such a common occurrence that typically, unless known risk factors are present, no special testing is performed. For couples who have experienced more than two miscarriages, diagnostic studies to detect genetic, hormonal, or anatomical problems may be recommended. Some doctors recommend evaluation of the couple after the second miscarriage, particularly if the woman is over 35 years of age.
What is the outlook for future pregnancies after a miscarriage?
Most women who miscarry subsequently go on to have a successful pregnancy. The likelihood of a miscarriage in a future pregnancy increases with the total number of miscarriages a woman has previously experienced. In general, the risk of recurrence in women who have had a previous miscarriage is about 15%. The risk is about 30% in women who have had two miscarriages. Most women will have their menstrual periodwithin 4 to 6 weeks after a miscarriage. Your doctor can advise you when you may start trying to conceiveagain. While it is possible to conceive again after your menstrual period has returned, some doctors advise waiting a bit longer, such as another menstrual cycle or more, to provide enough time for physical and emotional recovery.
Can miscarriage be prevented?
There is no evidence that bed rest can help prevent miscarriage, but women who have vaginal bleeding during pregnancy are often advised to rest and limit sexual activity until there are no more potential signs of miscarriage. It is possible that some risk factors for miscarriage can be minimized by maintaining a healthy weight and avoiding the use of alcohol, illicit drugs, or tobacco. Screening for, and treatment of, any sexually-transmitted diseases (STDs) can also reduce the risk of a miscarriage. In most instances, the prevention of a miscarriage is outside of the woman's control.
