Monday, December 17, 2007

Why Do Miscarriages and Stillbirths Happen?

The most common cause of pregnancy loss is a random chromosome abnormality that occurs during fertilization. For fertilization to occur, the chromosomes in the nucleus of both the egg and the sperm need to join into 23 pairs (46 total chromosomes). Sometimes this pairing does not happen correctly and that can impede the development of the fetus.

Other factors that could contribute to a miscarriage include:

• fertilization late after ovulation
• low or high levels of the thyroid hormone
• uncontrolled diabetes
• exposure to environmental and workplace hazards, such as radiation or toxic agents
• uterine abnormalities
• incompetent cervix, or when the cervix begins to open (dilate) and thin (efface) before the pregnancy has reached term
• certain medications (mostly prescription), such as the acne drug Accutane

Certain behaviors also increase the risk of a miscarriage. Smoking, for example, puts nicotine and other chemicals into the bloodstream that cause the blood vessels in the placenta to spasm, which decreases the blood flow to the uterus. Smokers also have a lower level of oxygen in their blood, which means the fetus gets less oxygen. Alcohol and illegal drugs have been proved to lead to miscarriages. There is no evidence that stress or sexual activity contributes to miscarriage.

Some of the common causes of a stillbirth include:

• pre-eclampsia and eclampsia, disorders of late pregnancy that involve high blood pressure, fluid retention, and protein in the urine
• uncontrolled diabetes
• abnormalities in the fetus caused by infectious diseases - such as syphilis, toxoplasmosis, German measles, rubella, and • influenza - or by bacterial infections like listeriosis
• severe birth defects (responsible for about 20% of stillbirths), including spina bifida
• postmaturity - a condition in which the pregnancy has lasted 41 weeks or longer
• chronic high blood pressure, lupus, heart or thyroid disease

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