Wednesday, April 06, 2016

Can PGD/PGS help to reduce the risk of a miscarriage?

Woman who miscarry after IVF treatment are often quite distraught . They worry about whether they'll be able to have healthy baby.

Miscarriage is a complex issue , which is hard to analyse for many reasons. For one, there are so many old wife's tales which shroud it , that women get confused and are not sure whom to believe.  This is because it is surprisingly common, which means that everyone and their grandmother has an opinion about what causes a miscarriage and how to prevent it, and are more than happy to share it. Because it causes so much emotional distress, women who have miscarried  are very vulnerable and find it hard to think straight. They are happy to clutch and straws and false hope.

Even doctors don't agree about what the cause of a miscarriage is in every patient. Because there are so many moving parts involved in a pregnancy loss, we often cannot pinpoint the right diagnosis in an individual patient .

While we do know that the commonest reason for a miscarriage is a genetic problem in the fetus, this is actually a "waste-paper basket" diagnosis, because it doesn't specify what the defect is in that particular embryo.

Inspite of this, many patients come to the apparently logical conclusion that " if we do IVF, genetically analyse the embryos using PGD, and then selectively transfer only the euploid
( chromosomally normal) embryos , then we will be able to reduce the risk of another miscarriage."  This sounds extremely sensible, but unfortunately doesn't work out well in real life.  Even women who've had IVF PGS with the transfer of euploid embryos can and do miscarry.

The reason for this is that the commonest reason for a miscarriage is not always aneuploidy.  An
aneuploid embryo is one where the number of chromosomes is abnormal,  and while these embryos will miscarry, aneuploidy is only one of the many causes for a miscarriage. The problem is that this is the only cause which PGS will allow us to pick up as far as the genetic reasons for a miscarriage go.

There are lots of other genetic reasons for a miscarriage . Thus, many embryos are euploid ( their chromosomes appear completely normal ) but they nevertheless still harbor defects at the gene level,  which prevent the embryo from growing beyond a particular phase, and result in a miscarriage.   Our genetic technology is still not mature enough to test for these, because the tests we have are still very crude.  This is why it's important that patients have realistic expectations , and doctors should not allow the promise of PGS to be over sold. Over promising causes a lot of heart burn , and when the patient does miscarry after PGD , this will end up in giving PGS/ PGD a bad reputation .

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