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A miscarriage is a pregnancy that ends before the fetus is considered “viable” (before 20 weeks of gestation). A fetus is viable if it can live outside the mother’s womb. Pregnancy losses after the 20^th week of gestation are known as preterm deliveries.

A woman’s reproductive system includes the uterus, cervix, two ovaries, two fallopian tubes and the vagina. The fallopian tubes are narrow tubes that connect the ovaries to the uterus. Once a month, an egg is released by one of the ovaries, and travels down the fallopian tube, where it may be fertilized by sperm.

Once the egg and sperm join, they rapidly begin to develop new cells. This bundle of cells, called the embryo, normally implants on the inner wall of the uterus. Once implanted, the embryo continues to grow inside a sac of amniotic fluid, contained within the placenta. After several weeks, the embryo is called a fetus.

In a miscarriage, the woman’s body expels all or some of the fetus, the placenta and the fluid surrounding the fetus. The medical term for miscarriage is spontaneous abortion. It is also referred as early pregnancy loss.

According to the National Institutes of Health (NIH), up to 50 percent of all fertilized eggs die and are spontaneously aborted, usually before a woman even realizes that she is pregnant. Among known pregnancies, the rate of miscarriage is approximately 25 percent, according to the American Society for Reproductive Medicine (ASRM). Miscarriage usually occurs between the 7^th and 12^th week of pregnancy (during the first trimester).

In many cases, chromosomal abnormalities in the fertilized egg prevent it from developing normally and the pregnancy terminates naturally. Typically, such problems are the result of errors that occur by chance as the embryo divides and grows.

In other cases, complications may occur during the delicate process of early human development that may prevent an embryo from continuing gestation. For example, the egg may not implant properly in the uterus or the embryo may have structural defects that do not allow it to continue growing inside the mother’s uterus (womb).

In all cases, spontaneous expulsion of the pregnancy is preceded by death of the embryo or fetus. Sometimes a miscarriage may be accompanied by an infection in the uterus (septic miscarriage). This is a serious condition that can result in shock and organ failure, which requires prompt medical treatment.

When a woman experiences the loss of two or more consecutive pregnancies in the first or second trimester OR the loss of three or more pregnancies before 20 weeks gestation, she is experiencing recurrent miscarriage. Other terms for this condition include: recurrent spontaneous miscarriage, recurrent spontaneous abortion and recurrent pregnancy loss.

According to the ASRM, less than 5 percent of women will experience two consecutive miscarriages, and only 1 percent will experience three or more miscarriages.

A woman who experiences recurrent miscarriage is typically subject to more diagnostic tests than a woman who has a single, first trimester miscarriage. However, in 50 to 75 percent of couples who experience recurrent miscarriage, no explanation is found, according to the ASRM. Treatment options for recurrent miscarriages depend on the cause of the miscarriages and usually differ from standard miscarriage treatment options.

Couples may be comforted to know that, according to the ASRM, pregnancy is successful in 60 to 70 percent of women who experience unexplained recurrent pregnancy losses.