What is a miscarriage?

Also known as a spontaneous abortion, a miscarriage is defined as the loss of your pregnancy before 20 weeks' gestation. It occurs in about 10 to 15% of all pregnancies. The most common cause of miscarriage is chromosomal abnormality in the embryo.

Miscarriage usually happens in the first trimester -- that is, during the first 12 weeks of pregnancy. After four months, it's much less likely to occur. However, the risk of miscarriage increases with age.

A miscarriage is the end of a pregnancy due to natural (and often unknown) causes before week 20. Many miscarriages seem to be the result of chromosomal abnormalities that affect the fetus's growth. Others may be due to the mother's anatomy or infection, among other causes. Miscarriages take place in about 15 percent of all known pregnancies. This means that the prevalence may be even higher for miscarriage since some women have one so early that it may be mistaken for menstruation.

A miscarriage essentially occurs when there's a hemorrhage in a layer of tissue in the uterus. The bleeding causes a breakdown of tissues next to the ovum, and that stimulates uterine contractions-contractions that result in the fertilized egg detaching from the uterine lining and thus being expelled by the mother. Sometimes, women aren't even aware the whole pregnancy/miscarriage even occurred.

Boston Women's Health Book Collective
Administration Specialist

An estimated 15 to 20 percent of known pregnancies end in miscarriage, the loss of a pregnancy before the twentieth week. Most clinically recognized miscarriages occur between the seventh and twelfth week after a woman's last menstrual period.

The vast majority of miscarriages cannot be prevented. Early losses often occur without a detectable embryo. Up to 70 percent of first-trimester miscarriages, and 20 percent of second-trimester miscarriages, are caused by chromosomal anomalies from either the sperm or the egg cell. Other known causes that are more likely to result in later miscarriages include infection, abnormalities of the uterus or cervix, smoking, substance abuse, exposure to environmental or industrial toxins, and autoimmune diseases. A serious physical trauma could cause a miscarriage. In rare cases, women miscarry after certain tests during pregnancy, such as chorionic villus sampling (CVS) or amniocentesis.Many women learn about a miscarriage at a routine prenatal visit before experiencing any physical symptoms. The first symptoms of miscarriage are usually spotting or bleeding, followed by cramps in your lower back or abdomen. Other signs include fluid or tissue passing from the vagina.

Roughly two out of five pregnant women experience some vaginal bleeding or spotting during pregnancy and only half of these women will miscarry. If you have any vaginal bleeding during pregnancy, your health care provider can help determine if the bleeding is likely to result in miscarriage or if it has another cause that does not threaten the pregnancy. If you are miscarrying, bleeding will become heavier and cramping can be painful as the cervix dilates.

If a blood test or sonogram indicates that you have had or are about to have a miscarriage, you may have a few options. Some women choose to allow the miscarriage to occur and complete itself naturally. Others find that scheduling a termination provides a sense of control and closure.

Once everything in your uterus has been expelled, bleeding will continue, lessening over several days. If bleeding increases or if you have foul-smelling discharge or a fever, contact your health care provider. If fetal tissue remains in your uterus, your provider can perform a D&E to remove it and thereby prevent infection.

If your blood type is Rh-negative, you will need a shot within 72 hours of the miscarriage.

Dr. Kevin W. Windom, MD
OBGYN (Obstetrician & Gynecologist)

A miscarriage is the spontaneous loss of a pregnancy. This is most commonly seen prior to 20 weeks pregnant.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.