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Spontaneous interruption of pregnancy called miscarriage. Medical synonym for miscarriage is spontaneous abortion.

World Health Organization (WHO) defines this unsurvivable state as an embryo or fetus weighing 500 grams or less, which typically corresponds to a fetal age (gestational age) of 20 to 22 weeks or less. Miscarriage occurs in about 15% to 20% of all recognized pregnancies; in most cases it occurs before the 13 week of pregnancy. With the development of highly sensitive assays for hCG levels that can detect an early pregnancy even prior to the expected next period, researchers have been able to show that about 65%-70% of all pregnancies (recognized and not-recognized) are lost. Because the loss occurs so early, many miscarriages occur without the woman ever having known she was pregnant.

About 15% of fertilized eggs are lost before the egg even has a chance to implant in the uterus wall. Women would not be able to identify this type of miscarriage. Another 15% of conceptions are lost before eight weeks’ gestation. Once fetal heart function is detected in a given pregnancy, the chance of miscarriage is less than 5%.

Miscarriage Causes


Most common causes of miscarriage in the first third of pregnancy (first trimester) are:

  • chromosomal abnormalities,
  • collagen vascular disease (such as lupus),
  • hormonal dysfunctions,
  • diabetes,
  • infections,
  • uterus abnormalities,
  • stress.

Chromosomal abnormalities. Certain genetic abnormalities are known to be more prevalent in couples that experience repeated pregnancy losses. These genetic traits can be screened for by blood tests prior to trying to conceive.

Half of the fetal tissue from1st trimester miscarriages contain abnormal chromosomes. This number drops to 20% with 2nd trimester miscarriages.

Chromosomal abnormalities also become more common with aging, and women over age 35 have a higher rate of miscarriage than younger women. Advancing maternal age is the most significant risk factor for early miscarriage in otherwise healthy women.

Collagen vascular diseases are illnesses in which a person’s own immune system attacks their own organs. These diseases can be potentially very serious, either during or between pregnancies. In these diseases, a woman makes antibodies to her own body’s tissues. Examples of collagen vascular diseases associated with an increased risk of miscarriage are systemic lupus erythematosus, and antiphospholipid antibody syndrome. Blood tests can confirm the presence of abnormal antibodies and are used in the diagnose of these conditions.

Hormonal dysfunctions. Hormones (mainly estrogens and progesterone) are crucial in pregnancy development and any dysfunction can be a cause for pregnancy interruption. Some hormonal diseases can provoke hormonal disturbances – Cushing’s Syndrome, thyroid disease, and polycystic ovary syndrome (PCOS). It also has been suggested that inadequate function of the corpus luteum in the ovary (which produced progesterone necessary for maintenance of the very early stages of pregnancy) may lead to miscarriage – “luteal phase defect”.

Diabetes generally can be well managed during pregnancy, if a woman and her health care practitioner work closely together. However, if the diabetes is insufficiently controlled, not only is the risk of miscarriages higher, but the baby can have major birth defects. Other problems can also occur in relation to diabetes during pregnancy. Good control of blood sugars during pregnancy is very important.

Infections are recognized as an increased risk for miscarriage. Fetal or placental infection by the offending organism then leads to pregnancy loss. Examples of infections that have been associated with miscarriage include infections by Listeria monocytogenes, Toxoplasma gondii, parvovirus B19, rubella, herpes simplex, cytomegalovirus, and lymphocytic choriomeningitis virus.

Uterus abnormalities (congenital defects, tumors). Normal pregnancy development needs normal uterus size and structure. In some women there can be a tissue bridge (uterine septum), that acts like a partial wall dividing the uterine cavity into sections. The septum usually has a very poor blood supply, and is not well suited for placental attachment and growth. Therefore, an embryo implanting on the septum would be at increased risk of miscarriage.

Some fibroids also can provoke miscarriage. Fibroid tumors are benign growths of muscle cells in the uterus. While most fibroid tumors do not cause miscarriages, some can interfere with the embryo implantation and the embryo’s blood supply, thereby causing miscarriage.
Some post-operation uterus scars also can be a problem for normal pregnancy development.
Sometimes surgical procedures also can be a cause for miscarriage such as amniocentesis, cervical procedures even appendectomy.

Stress. There isn’t enough evidence to show whether or not stress is a risk factor for spontaneous abortion, but it’s a good idea to take time during the day to relax.

Check “Miscarriage symptoms, risk factors and prevention” on next page.

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