Sex Selection / PGS / PGD
Embryo biopsy and advanced genetic testing allows us to know that an embryo has the correct number of chromosomes before it is transferred. The biopsy techniques have been perfected and studies have shown that biopsies done on the fifth day of culture do not measurably change the embryos’ potential to implant and grow into a baby. There are three different procedures possible after the biopsy has been done.
With sex selection, it is determined if the embryo carries a male chromosome or not. More specifically, it is determined if there are two X chromosomes, and therefore the embryo is a girl, or if there is one X and one Y, and therefore the embryo is a boy. With simple sex selection, the remainder of the chromosomes are not looked at so this procedure does not reduce the miscarriage rate or improve pregnancy rate. For example, since the number of autosomes (the 22 chromosomes that are not sex chromosomes) is not counted, sex selection would not detect an embryo with 3 chromosomes 21 – Down’s syndrome. We no longer do simple sex selection because of this. Standard PGS counts all the chromosomes and therefore also improves the delivery rate and reduces miscarriage rates.
Most labs will allow you to request that the sex not be reported if the ability to sex select is a problem for you.
PGS (Preimplantation Genetic Screening)
This technique will tell us if the embryo is 46 XX, 46 XY, or some abnormal count like trisomy 21 (Down’s syndrome). It cannot tell you if a particular gene is normal or abnormal. It can only tell you if a large part of one or more chromosomes is missing or duplicated indicating a major genetic abnormality. This technique will improve the pregnancy rate and reduce the miscarriage rate. It has primarily been used in older women though in many programs, the majority of women at all ages use PGS. With older women, the idea is that you don’t want to waste time with miscarriages so you want to know which embryos are normal and if none are normal, you can immediately start into the next cycle.
PGD (Preimplantation Genetic Diagnosis)
This was the original reason for doing embryo biopsies. In this situation, the couple is known to be at risk for having a baby, or another baby, with a genetic disease such as cystic fibrosis, or sickle cell, or fragile X, or one of several hundred other genetic diseases. You must know exactly what you are looking for. The lab must look at the mutations in the parents first and verify that they can make the diagnosis before an IVF cycle can be started. Because of the work involved, this is also the most expensive type of genetic testing but also the only one likely to be covered by insurance. In some cases, an insurance company will pay for this and the IVF cycle even when IVF is not a covered expense. It is much cheaper for them to do this than to pay for the care of a sick child. PGS is frequently done on the same sample to rule out a major chromosomal problem.