In 2 percent to 4 percent of couples with recurrent loss, one partner is found with a problem, a genetically balanced rearrangement of chromosomes. He or she is normal, but when the egg or sperm is formed, it can end up with an extra chromosome piece or a missing segment, resulting in an embryo that cannot survive. In such cases, a couple may choose in vitro fertilization, with genetic analysis of the resulting embryos performed to select a chromosomally normal one for implantation.
Structural abnormalities of the uterus are found in 10 percent to 15 percent of women who have recurrent miscarriages, though experts disagree over whether these problems impede a successful pregnancy. Likewise, the role of fibroids and endometriosis is controversial, and surgery to remove such extra tissue may not prevent another miscarriage.
A TREATMENT THAT CAN HELP
An autoimmune disorder that involves the production of antibodies to phospholipids, which are important components of blood vessel walls, can sometimes cause clots in the small blood vessels of the placenta. The resulting damage can cause recurrent miscarriage. In women with high levels of such antibodies, treatment with the blood thinner heparin and low-dose aspirin can reduce, though not necessarily eliminate, the risk of repeated miscarriage, Carson said.
Although there is no good evidence that a woman's immunity to her partner's tissues is responsible for repeated miscarriage, suggestive evidence indicates that an immune abnormality may occur that interferes with producing the intrauterine growth factors needed for a successful pregnancy. But there is no proven treatment for such a problem.
One popular notion to explain recurrent miscarriage is inadequate production of progesterone, the hormone released after ovulation that prepares the uterus for pregnancy. This idea has resulted in many efforts to support an incipient pregnancy by administering progesterone, a treatment that Carson described as harmless but not likely to be effective. Some researchers suggest that if a hormonal problem exists it may begin before the egg is released and that drugs to stimulate ovulation may be more helpful.
Even after the most thorough work-up, half to three-fourths of couples with recurrent pregnancy loss "will have no certain diagnosis," the report states. For such couples, the best medicine is good information and sympathetic counseling, combined with optimistic statistics. "Live birth rates between 35 percent and 85 percent are commonly reported in couples with unexplained recurrent pregnancy loss who undertake an untreated or placebo-treated subsequent pregnancy."
A combined analysis of the best studies available in 1995 showed that 60 percent to 70 percent of women with unexplained recurrent losses would have successful next pregnancies.
Of course, every woman contemplating pregnancy would be wise to follow the recommendations of the March of Dimes to start prenatal vitamin supplements before becoming pregnant. Throughout pregnancy, eat healthfully, exercise moderately, avoid alcohol, eat fish (but avoid seafood high in mercury), limit caffeinated drinks to two a day and check with the doctor before taking medications or dietary supplements.
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