Miscarriage is pregnancy loss that occurs before 20 weeks, before the fetus is able to survive outside the womb. About 15 percent of recognized pregnancies end this way (1). As many as 50 percent of all pregnancies may end in miscarriage, because many losses occur before a woman realizes she is pregnant (2).
Why do miscarriages occur?
The causes of miscarriage are not thoroughly understood. When a woman has a first-trimester miscarriage, her health care provider often cannot determine the cause. However, most miscarriages occur when a pregnancy is not developing normally. Usually, there is nothing a woman or her provider can do to prevent it.
Among factors known to cause first-trimester miscarriages, the most common is a chromosomal abnormality in the fetus. Chromosomes are the tiny thread-like structures in each cell that carry our genes, which dictate all traits from eye color to the workings of our internal organs. Each person has 23 pairs of chromosomes, or 46 in all, with one chromosome per pair coming from the mother and one from the father. Up to 70 percent of first-trimester miscarriages are caused by chromosomal abnormalities in the fetus (3).
Most chromosomal abnormalities result from a faulty egg or sperm cell. Before pregnancy, immature egg and sperm cells divide to form mature cells with 23 chromosomes. Sometimes, the cell splits unevenly, resulting in egg or sperm cells with too many or too few chromosomes. If a cell has the wrong number of chromosomes, the embryo has a chromosomal abnormality and is usually miscarried. Chromosomal abnormalities become more common with aging, and women over age 35 are at higher risk of miscarriage than younger women.
Chromosomal abnormalities also can result in a blighted ovum: a pregnancy sac that contains no fetus, either because the embryo did not form or because it stopped developing very early. In early pregnancy, the woman may notice that her pregnancy symptoms have stopped and she may develop dark-brown vaginal bleeding. An ultrasound examination will show an empty pregnancy sac. A blighted ovum will eventually result in miscarriage, though miscarriage may not occur for weeks. Because waiting for a miscarriage can be upsetting, doctors often offer the woman the option of emptying the uterus with a procedure called a D&C (dilation and curettage). However, waiting for a miscarriage to occur naturally should not harm a woman's health or chances for a healthy future pregnancy. A woman and her provider choose the approach that is best for her.
Other factors that can contribute to early miscarriage include hormonal problems, infections, and maternal health problems (such as poorly controlled diabetes, systemic lupus erythematosus, or thyroid disease). One study found that women with an infection called bacterial vaginosis were nine times more likely to have a miscarriage than uninfected women (4).
A mother's lifestyle may increase her risk of a first-trimester miscarriage. Women who drink alcohol, smoke cigarettes, or use illicit drugs may increase their risk for first-trimester miscarriage (5). A recent study found that women who consume 200 milligrams or more of caffeine every day are twice as likely as women who consume no caffeine to have a miscarriage. The March of Dimes recommends that women who are pregnant or trying to become pregnant consume no more than 200 milligrams of caffeine per day (equal to about one 12-ounce cup of coffee a day) (6). Another study suggested that women who use pain-relieving medications, such as non-steroidal anti-inflammatory drugs (such as ibuprofen) and aspirin, around the time of conception may also increase their risk of miscarriage (7).
Second-trimester miscarriage often is caused by problems with the uterus or by a weakened cervix that dilates prematurely. As with first-trimester losses, maternal infections and chromosomal abnormalities can cause later miscarriages. Chromosomal abnormalities appear to cause about 20 percent of second-trimester miscarriages (3). Certain maternal immune system problems (such as lupus) also can cause these losses.
What are the symptoms of miscarriage?
Vaginal bleeding, sometimes accompanied by menstrual-like cramps or more severe abdominal pain, can be a sign that a miscarriage is about to occur. However, many women experience spotting in early pregnancy and do not miscarry. A woman should contact her provider if she experiences any bleeding, even light spotting, in pregnancy. Her provider may do an internal examination to see if her cervix is dilated (a sign that a miscarriage is likely), and sometimes an ultrasound examination and blood tests.
What treatment is needed if a woman has a miscarriage?
Most women who have an early miscarriage do not need treatment. The uterus empties itself like a heavy period. However, a doctor may recommend a D&C in certain cases, such as if a woman is bleeding heavily, if she may have an infection, or if an ultrasound examination shows that there is tissue remaining in the uterus.
What tests are done following a miscarriage?
Doctors usually do not perform any tests following a first miscarriage that occurs in the first trimester. The cause of these early losses is often unknown, though chromosomal abnormalities are usually suspected. If a woman has a miscarriage in the second trimester or has two or more miscarriages in the first trimester, tests usually are recommended to help determine the cause. These can include:
- Blood tests (called a karyotype) to check for chromosome abnormalities in both parents and certain hormonal problems and immune system disorders in the mother
- Testing for chromosomal abnormalities in tissue from the miscarriage (if tissue is available)
- Ultrasound examination of the uterus
- Hysteroscopy (viewing the uterus through a special scope inserted through the cervix)
- Hysterosalpingography (an X-ray of the uterus)
- Endometrial biopsy (suctioning a small piece of uterine lining to check hormone effects)
What causes repeat miscarriages?
While miscarriage usually is a one-time occurrence, about 1 to 2 percent of couples experience two, three or more miscarriages in a row (3). In some cases, these couples have an underlying problem that is causing the miscarriages.
Couples who have experienced two or more miscarriages should have a complete medical evaluation. However, testing reveals the cause of repeat miscarriages in no more than 50 percent of couples (1).
Known causes of repeat miscarriage include:
- Chromosomal problems: Recent studies suggest that chromosomal problems usually occur only once, more recent studies suggest that chromosomal problems may cause nearly 50 percent of repeated losses (1). Most parents who suffer repeated miscarriages have normal chromosomes; however, there is a 2 to 4 percent chance that either partner carries a chromosomal rearrangement that does not affect his or her health, but can cause chromosomal abnormalities in the fetus that can result in miscarriage (1). Both parents should have a blood test (karyotype) to check for these chromosomal rearrangements.
- Uterine abnormalities: Abnormalities of the uterus cause 10 to 15 percent of repeated miscarriages (1). These miscarriages can occur in the first or second trimester. Some women are born with a uterus that is abnormally shaped, or partly or completely divided. Others develop noncancerous tumors (fibroids) or have scars in the uterus from past surgery. These abnormalities can limit space for the growing fetus or interfere with the blood supply to the uterus. Some uterine abnormalities can be surgically corrected, improving the outlook for future pregnancies. A weakened (sometimes called incompetent) cervix (opening of the uterus) can lead to miscarriage, usually between 16 and 18 weeks of pregnancy. Repeated miscarriage due to weakened cervix sometimes can be prevented by placing a stitch around the cervix early in the next pregnancy (a procedure called cerclage).
- Hormonal causes: When a woman's body produces too much or too little of certain hormones, the risk of miscarriage may increase. Low levels of the hormone progesterone, which is crucial to support an early pregnancy, may cause between 25 and 40 percent of early miscarriages, though this remains unproven (1). Women who have low levels of progesterone in repeated menstrual cycles, diagnosed by blood tests and endometrial biopsy, have what is called a luteal phase defect. Treatment with progesterone suppositories or injections of human chorionic gonadotropin may help prevent another miscarriage; however, studies have not yet proven that these treatments are effective. At least a third of women with multiple miscarriages appear to have polycystic ovary syndrome, characterized by hormonal abnormalities and multiple cysts on the ovaries.
- Immune system problems: While everyone produces proteins called antibodies to fight off infections, some people produce antibodies (called autoantibodies) that can attack their own tissues, causing a variety of health problems. Some types of autoantibodies (such as anticardiolipin) cause blood clots that can clog blood vessels in the placenta. Studies suggest that this and related antibodies (called antiphospholipid antibodies) cause between 3 and 15 percent of repeat miscarriages (1). Special blood tests can measure antibody levels. Treatment with low doses of aspirin and the blood-thinning drug heparin result in a healthy baby in 70 to 75 percent of affected women (1). A genetic abnormality called the factor V Leiden mutation, which affects blood clotting, also may play a role in repeat miscarriages. Researchers are investigating whether treatment with aspirin and heparin also may help prevent these losses.
- Infections and other factors: Certain symptomless infections of the genital tract may play a role in a small number of repeated miscarriages. However, routine testing (in women with no symptoms) for infections is not currently recommended. Workplace exposure to certain industrial solvents, by the pregnant woman or her partner, may cause miscarriage. Couples should discuss chemicals in their workplace with their health care provider.
Even if the cause of their repeated miscarriages cannot be found, couples should not lose hope. Even without treatment, about 60 to 70 percent of women with repeated miscarriages will have a successful next pregnancy (1).
How long does it take to recover from a miscarriage?
It takes weeks to a month or more for a woman to recover physically, depending upon how long she was pregnant. Some pregnancy hormones remain in the blood for one to two months after a miscarriage. Most women experience a menstrual period four to six weeks after a miscarriage.
Often, it takes much longer to recover emotionally. Couples may experience intense grief as they mourn their loss. A woman may experience many emotions including numbness, sadness, guilt, depression, anger, and difficulty concentrating. She and her partner may handle their grief in different ways, creating tension between them at a time when they need each other most. They should not hesitate to ask their health care provider for a referral to a counselor who is experienced with dealing with pregnancy loss. Many couples also benefit from support groups.
How long should a woman wait after a miscarriage before attempting another pregnancy?
A woman should not attempt to become pregnant again until she is physically and emotionally ready and she has completed any tests recommended to determine the cause of the miscarriage. Medically, it appears safe to conceive after a woman has had one normal menstrual cycle (if she is not undergoing tests or treatments for the cause of her miscarriage). However, it may take much longer before a woman feels emotionally ready to attempt pregnancy.
Resources
Parents or other family members who have experienced the loss of a pregnancy may want to read the bereavement information provided on this Web site.
