Causes of Miscarriage

A miscarriage is a pregnancy that ends in the first 20 weeks. About 15 percent of known pregnancies will end in miscarriage, usually in the first trimester. After 20 weeks, it is called a stillbirth.


Most miscarriages are random events caused by chromosomal abnormalities in the fertilized egg - usually because the egg or sperm had the wrong number of chromosomes, preventing normal development. Other causes of miscarriage include an egg that does not implant properly or an embryo with structural defects. In some cases, chromosomal problems in the fertilized egg can lead to a blighted ovum - a situation where the placenta and gestational sac begin to develop, but the embryo either fails to develop or stops before there is a heartbeat. Once the heart has started beating, the chances of miscarrying drop dramatically.

A miscarriage can happen to any woman, but there are some factors known to increase the chances. Increasing age (in both the mother and the father) increases the odds of miscarriage. Certain diseases such as lupus, poorly controlled diabetes, and some hormonal disorders can increase the risk. Problems with the uterus or cervix and a family history of certain genetic problems can lead to miscarriage. Smoking, drinking, and recreational drugs can cause a miscarriage, as can some prescription and over-the-counter medications.

In some cases the loss of the pregnancy is discovered during a routine prenatal visit, when the uterus measures small or the practitioner can't find a heartbeat. It's not unusual for the embryo or fetus to stop developing a few weeks before there are symptoms such as bleeding; usually, though, spotting or bleeding will be the first sign of a miscarriage - though spotting does not always mean a miscarriage is about to happen.

If spotting appears, the practitioner should be notified right away. If it is a miscarriage, there may be abdominal pain, which can feel crampy or persistent, mild or sharp. There may be lower back pain or pelvic pressure. The placenta and embryonic or fetal tissue may be passed, which will look grayish and may contain blood clots. If this happens, this tissue should be saved if possible, in a clean container in case the practitioner wants it tested.

While distressing, it's important to remember that most first miscarriages are random events that will not be repeated. Chances are that a subsequent pregnancy will bring a much healthier and happier outcome.

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