Chromosome Errors Cause Most Miscarriages

The ticking of your biological clock involves not only an increased incidence of infertility with the advancing years, but also a dramatic increase in miscarriage. Over 25 percent of pregnancies in women over age thirty-six end in miscarriage, and that figure below percent for women over forty. More than 90 percent of miscarriages are caused by chromosomal and genetic errors in the embryo. We’ve already discussed in the previous chapter how we can prevent trisomy 21 (Down syndrome) pregnancies with PGD. The same PGD technique can be attempted to prevent recurrent miscarriage.

Women with recurrent miscarriage usually produce embryos that have an abnormal number of chromosomes. However, an occasional embryo from such patients will be normal. Rather than just allowing these otherwise fertile women to get pregnant spontaneously and miscarry over and over again, we can do IVF, obtain as many as fifteen or more embryos, and test them each before transfer back into the woman’s uterus. The one or two embryos that are actually normal can be placed into her uterus so that she can then carry a normal, healthy full-term pregnancy, without the fear of one heartbreaking miscarriage after another.

There is a lot of confusion about miscarriage. In order to really understand miscarriage, you would have to perform a karyotype (i.e., analysis of chromosomes) on the products of conception immediately if there is an early sign on ultrasound of fetal demise. Waiting until the natural passing of the products of conception will make diagnosis impossible. Often, the fetal karyotype will show a normal 46XX, but this is simply caused by contamination with maternal cells. This occurs because the products of conception are passed so late after the fetal demise that the DNA of the fetus is completely degenerated, and the only living cells to grow and culture in the karyotype test are the mother’s. That is why there has been a misconception over the previous decades that only 50 percent or less of miscarriages are caused by chromosomal error. Dr. Mary Ann Perle of New York University has shattered that myth. Detailed testing with an early D and C and careful dissection the moment the fetal heartbeat stops, before the tissue has had a chance to degenerate, demonstrates that most miscarriages are caused by chromosomal and genetic errors in the embryo itself, and not by problems in the uterus or in the woman’s general system.

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