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A major cause of miscarriage is an abnormality in the developing fetus resulting from genetic error. One study reports that 50-60% of all miscarriages in the first three months of pregnancy are due to chromosomal abnormalities.
Abnormal Hormone Levels
Abnormal hormone levels may cause miscarriage because the uterine lining does not develop sufficiently for the implantation and nourishment of the fertilized egg. Women with thyroid and adrenal gland problems and women with diabetes are at a higher risk for miscarriage due to hormonal imbalances. In addition, an elevated prolactin level can disrupt normal uterine lining development.
Structural problems of the uterus may cause miscarriage, usually by interfering with the implantation of the fertilized egg. Uterine myomas (fibroids) are non-cancerous growths in the uterine wall. Fibroids can cause infertility if they are blocking the opening of the fallopian tube(s) or if their position is affecting the normal functioning of the uterine lining. A septum, a fibrous wall which divides the uterine cavity, can cause poor implantation and easily pregnancy loss. DES exposure, resulting in a T-shaped uterus also contributes to pregnancy loss.
Another cause of miscarriage is an incompetent cervix, meaning the cervical muscle is weak and that it cannot remain closed as the developing fetus reaches a certain weight and puts pressure on the cervical opening.
Infections such as German measles (rubella), herpes simplex, ureaplasma, cytomegalovirus and chlamydia can affect fetal development and in some cases, result in miscarriage. RESOLVE has a Fact Sheet on "Infections and Infertility."
Toxins in the air around you can also result in fetal damage or miscarriage, especially if you experience regular exposure after 20 weeks of pregnancy. Studies indicate that the use of marijuana, tobacco, caffeine and alcohol all can affect fetal development and result in miscarriage. Most doctors suggest that women limit or avoid their use during pregnancy.
One category of immunologic problems that can cause miscarriages are the antiphospholipid antibodies. Blood tests are used to detect the presence of these antibodies. If present, medication that helps thin the blood may be used. The choices are: baby aspirin (81 mg) daily, often starting at ovulation and extending into the pregnancy, and/or Heparin, a drug given by injection and used to thin the blood.
Another category of immunologic causes of miscarriage are those that prevent the woman's normal protective response to the embryo.