The loss of a pregnancy before the 20th week of gestation is a miscarriage. Between 10 and 25 percent of clinically diagnosed pregnancies end in miscarriage. Because miscarriage can occur before a woman even realizes she is pregnant, the actual percentage of pregnancies that end is miscarriage is much higher. Women are most likely to miscarry between the fourth and sixth weeks of pregnancy. After the eighth week, the chances of miscarrying drop to less than five percent, and continue to decline for the rest of the pregnancy.
What Happens During a Miscarriage?
What happens during a miscarriage depends on when the miscarriage occurs and what causes it. Early miscarriages are often caused by embryonic chromosomal abnormalities resulting from malformed sperm or egg cells or a cell division problem during the blastocyst stage of development. This issue usually results in chemical pregnancy, or a pregnancy that ends before implantation even occurs. Chemical pregnancies account for approximately 50 to 75 percent of all miscarriages. The only sign of this type of miscarriage may be some light bleeding. When an egg implants and develops a placenta and a membrane but fails to develop an embryo, it is called a blighted ovum, which results in a miscarriage before the 12th week. A miscarriage due to intrauterine fetal demise occurs when the egg has implanted into the uterine lining and there is an embryo present, but it is already dead. In a molar pregnancy, miscarriage results when a fertilized egg implants into the uterine lining and an embryo begins to develop, but a colony of cysts also develop on the placenta, leading to the death of the embryo. Depending on whether the fetal tissue is completely expelled or not, any of these scenarios can lead to either an incomplete miscarriage or a complete miscarriage. An incomplete miscarriage occurs when the embryo or fetus is no longer viable, but it has not yet been expelled by the body. A complete miscarriage occurs when the body naturally expels all the fetal tissue. In the case of an incomplete miscarriage, medical intervention may be necessary, as the presence of the nonviable fetal tissue can be dangerous to the mother.