A pregnancy that ends before 20 weeks is called a miscarriage. Most miscarriages happen before the end of the first trimester (before 12 weeks). Many occur before a woman even knows she is pregnant. In the past, a woman who miscarried several times might never know why it happened. Today, more and more women are finding out the causes of their recurrent miscarriages.
The American College of Obstetricians and Gynecologists currently defines recurrent miscarriage as two to three, or more, consecutive pregnancy losses in the first trimester or early second trimester.
Miscarriages are not uncommon. It is estimated that every woman has a 10 to 15 percent chance of having a confirmed pregnancy (identified by a pregnancy test or a missed period) end in miscarriage.
For women who have had one miscarriage, their chances of carrying the next pregnancy to full term remain about the same as if they had never had one. The chance of miscarrying again after two miscarriages increases with each loss. The risk for recurrent miscarriage increases with age. Women 40 years or older with previous recurring miscarriages have a much higher risk compared to younger women.
There are many different reasons for miscarriage, including fetal chromosomal defects, hormonal problems or abnormalities of the uterus. But the cause is unknown in up to 75 percent of recurrent miscarriages, according to the American Society for Reproductive Medicine (ASRM). Some doctors are hesitant to begin testing and treatment until after three successive miscarriages, or after a second miscarriage if the woman is older than 35, because much of the testing and treatment is controversial, and the reasons that treatments work are not well understood.
It is also likely that a woman who suffers recurrent miscarriages will go on to have a healthy baby. According to the ASRM, 60 to 70 percent of couples with unexplained recurrent pregnancy losses will go on to have a healthy pregnancy. The group recommends a healthy lifestyle and folic acid supplementation, as well as smoking cessation, weight control, and reducing alcohol and caffeine. Informative and sympathetic counseling appears to play an important role in these patients' success.
Ask your doctor about the following possible causes of miscarriage.
Problems with the genes or chromosomes of the fetus are the most common causes of miscarriage with first pregnancy losses. These are usually not problems inherited from parents, but occur spontaneously, by chance, in the embryo. They are less commonly the cause for women with recurrent miscarriage.
Uterine abnormalities are associated with both first and second trimester pregnancy losses. Congenital abnormalities include double uterus and uterine septum. Other abnormalities include uterine polyps, fibroids and scar tissue inside the uterine cavity.
Incompetent cervix complicates about 1 percent of pregnancies. Women with an incompetent cervix often have rapid miscarriages between 16 and 18 weeks. This condition can be successfully treated with a stitch to help hold the cervix closed.
There are no infections that are known to cause recurrent miscarriages.
Exposure to certain solvents, either by the pregnant woman or her partner, sometimes may cause miscarriage. Couples should discuss any chemicals in the workplace with their doctor.
By doing a biopsy of the lining of the uterus, doctors can test for a luteal phase defect, which means that the body secretes too little progesterone during the luteal phase of the menstrual cycle. This is thought to be a factor in some cases of recurrent miscarriage. The relationship between luteal phase defect and recurrent pregnancy loss remains a subject of controversy, however, according to the American College of Obstetricians and Gynecologists. There is no conclusive data that treating a woman with progesterone or fertility medication is effective against recurrent pregnancy loss.
Maternal endocrine disorders such as uncontrolled diabetes or severe thyroid abnormalities have also been linked to miscarriage.
Smoking is a cause of recurrent miscarriage. Women should not smoke and also should avoid alcohol during pregnancy.
According to the ASRM, there is some evidence that certain abnormalities in the DNA from a man's sperm may increase miscarriage risk. It is not known, however, how often sperm defects contribute to recurrent miscarriage.
Immunology is the study of how the body recognizes something foreign or different and makes antibodies to protect itself. An immune problem called antiphospholipid syndrome is the cause for recurrent miscarriage in 3 to 15 % of women. The College recommends that women with recurrent miscarriage be tested for lupus anticoagulant and anticardiolipin antibodies (cardiolipins are a type of phospholipids).
A woman with antiphospholipid antibodies and lupus-like anticoagulant can be treated with low-dose aspirin and heparin. This therapy can increase blood flow to the placenta by inhibiting the tendency for clotting.
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