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- At best, about 90% of abnormal embryos can now be detected using PGD techniques.
- A relatively large number of eggs or embryos may be found to be abnormal and therefore leave few embryos for replacement. In some cases (11%), no eggs or embryos may be normal. In these cases, embryo replacement will not be recommended. Though this is a disappointing outcome, it is likely that without PGD the IVF cycle would not have resulted in a pregnancy or that an abnormal fetus would have resulted.
- The cells to be removed are studied with specialized new techniques. Such procedures may fail due to technical malfunctions.
- Not all chromosomal or genetic abnormalities can be determined with these procedures, since only a restricted number of chromosomes can be diagnosed at one time during the course of a single procedure.
- It is possible that a normal embryo may be incorrectly identified as being abnormal and not be replaced, or that an abnormal embryo is incorrectly identified as being normal and replaced into the uterus. (PGD is not currently considered a replacement for prenatal testing. Prenatal diagnosis is recommended to confirm the prognosis).
- Genetic and developmental damage (0.1%) to the embryo may accidentally occur during removal of the cell(s).
- Unknown technical circumstances in the laboratory may cause failure of the testing process, making results unavailable. Failure of the testing process has no effect whatsoever on your embryos. In this case, embryos will be selected for transfer based on existing criteria.
- Analysis of a single cell has limitations. Occasionally, chromosome anomalies are present in one cell, but not in other cells of the same embryo, or vice-versa, resulting in mosaicism. This may lead to transfer of an abnormal embryo, or discard of a normal embryo.
- PGD for translocation testing can determine the presence or absence of a certain chromosomal disorder, but cannot detect genetic disease nor predict genetic malformation.
- Even with a successful PGD procedure, pregnancy may not occur.
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