Preimplantation Genetic Diagnosis and Human Implantation—A Review
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Reduction of multiples and frozen embryos PGD of aneuploidy may also help reduce the number of multiple pregnancies. In the two latest studies involving a test and a control group, significantly fewer embryos were trans- ferred in the PGD groups than in control groups (Gianaroli et al., 1999; Munné et al., 1999, 2003; Werlin et al., 2003). In addition, because many embryos are abnormal, after PGD there are fewer chromosomally normal embryos remain- ing in excess of those for replacement. Therefore there are very few embryos freezable, which will alleviate the problem of accumulating, storing and eventually disposing of unwanted frozen embryos
This is why PGD is becoming more and more routine (originally it was used only where one or both parents carried a serious genetic disease). Most embryos are abnormal -- not just "not perfect", but not capable of developing beyond the first days or weeks of pregnancy. In young women about half are normal; in women over 40 about 10% are normal (with wide individual variation of course). In IVF without PGD, this means that in order to have a reasonably good chance of producing one baby, 2-5 embryos are transferred (number depending mostly on the mother's age).
But the laws of chance and unpredictable individual variation result in some high order multiple pregnancies which often end disastrously. While PGD doesn't provide a 100% guarantee of a baby, it greatly reduces the problem of multiples, and of the emotional strain of miscarriages in women who have usually already been through a lot of strain over years of unsuccessful efforts to have a baby.