Most first-trimester miscarriages are caused by chance chromosomal errors that happen when the embryo is first forming. (Chromosomes are parts of a cell that carry a person's genes.) This is usually a one-time event that does not repeat itself in a woman's next pregnancy.

Many miscarriages have no known cause.

After the first 12 weeks of pregnancy, or when the fetal heartbeat is seen on ultrasound, miscarriage risk drops significantly.3

Risk factors that may increase chances of a miscarriage include:

Increasing age, especially at age 35 and older.

A history of two or more miscarriages.

Nonsteroidal anti-inflammatory drug (NSAID) use (such as ibuprofen or naproxen) at the time of conception or during early pregnancy.

Alcohol or drug use during pregnancy.

Cigarette smoking during pregnancy.

Exposure to dangerous chemicals, such as benzene, arsenic, or formaldehyde, before or during pregnancy.

Heavy caffeine use during pregnancy.

Certain gynecological problems, such as uterine fibroids or other abnormalities of the uterus.

Disease or infection during pregnancy, including an autoimmune disease.

Physical trauma.

An immunologic cause—a woman's immune system rejects the pregnancy—which is a factor in a small number of miscarriages.
Recent research suggests that low folic acid levels may also increase the risk of miscarriage.
It is unusual for a woman to have three or more miscarriages. Repeat miscarriages can be caused by an underlying medical problem. Known causes of repeat miscarriage include polycystic ovary syndrome, a blood-clotting disorder called antiphospholipid antibody syndrome, an abnormal uterus, and a chromosome abnormality in either parent.

After a miscarriage, am I at risk for miscarrying again?

Miscarriage is usually a chance event, not a sign of an ongoing reproductive problem. If you have had one miscarriage, your chances for future successful pregnancies are good. Less than 1% of women have three or more miscarriages in a row (called recurrent miscarriages).

If you have had three or more miscarriages, talk to your health professional about testing and treatment for a possible underlying cause
Risk factors for miscarriage.

A history of miscarriages on your mother's side of the family.

Polycystic ovary syndrome, which can cause ovulation problems, obesity, increased male hormone levels, and an increased risk of diabetes.

A poorly controlled ongoing disease (such as diabetes or an autoimmune disease).

Certain bacterial or viral infections during pregnancy.

A blood-clotting disorder such as antiphospholipid antibody syndrome.

Problems with the structure of the uterus (such as a T-shaped uterus). Between 12% and 15% of women who have recurrent miscarriages have problems with the structure of the uterus.

A history of pregnancy with a birth defect.

A physical injury.

A chorionic villus sampling (CVS) or amniocentesis to test for birth defects or genetic problems. (CVS has a slightly higher risk of miscarriage [1 in 100] than amniocentesis [1 in 200].)

There are also known factors that do not increase the risk of miscarriage, such as exposure to computer monitors or electric blankets, sexual intercourse, and exercise.

Coping with a miscarriage

It is normal to go through a grieving process after a miscarriage, regardless of the length of your pregnancy. Guilt, anxiety, and sadness are common and normal reactions after a miscarriage. It is also normal to want to know why a miscarriage has happened. However, in most cases a miscarriage is a natural event that could not have been prevented.

To help you and your family cope with your loss, consider meeting with a support group, reading about the experiences of other mothers, and talking to friends or a counselor or member of the clergy. For more information, see the topic Grief and Grieving.

Your local bookstore or library may have books on coping with miscarriage. Also, your health professional will be able to address your questions and concerns about the miscarriage.

The intensity and duration of the grief varies from woman to woman, but most women find that they can return to the daily demands of life in a fairly short time. It is important to call your health professional if you have symptoms of depression that last for more than 2 weeks.15 The loss and the hormonal swings that result from a miscarriage can cause symptoms like postpartum depression.

A healthy, full-term pregnancy is possible for most women who have had a miscarriage, and even after having repeated miscarriages. If you want to become pregnant again, check with your doctor or nurse-midwife. Most health professionals recommend waiting until you have had at least one normal menstrual period before attempting to become pregnant after a miscarriage.