If you are having IVF treatment, preimiplantation genetic testing can improve your chances of having a healthy baby. These tests are done on embryos in early stages of development to find the healthiest embryos for transfer in an IVF cycle. Your doctor may recommend PGD or PGS for several reasons. Some fertility centers also offer genetic testing for family balancing.
Genetic testing is performed on embryos produced in an IVF cycle. In these tests, a few cells are removed from embryos for testing, called an embryo biopsy, and the embryos are frozen. The embryo cell samples are sent to the genetics laboratory for testing. Your reproductive endocrinologist will receive a report identifying the genetic quality of each embryo that was tested. The report will help your doctor select the best quality embryos for transfer in your next cycle.
Preimplantation Genetic Diagnosis (PGD)
PGD is used to test for specific genetic diseases. Your doctor will recommend this test if you and/or your partner are a carrier for a genetic disease. Some of the diseases that can be tested for are hemophilia, cystic fibrosis, Tay-Sachs disease, sickle cell anemia, fragile X syndrome, hereditary breast or ovarian cancer syndrome (BRCA1 and BRCA2), Huntington disease, hereditary cardiomyopathy, Gaucher disease, and Duchenne muscular dystrophy. PGD can also be used for HLA matching, if you are hoping to have a child who can donate bone marrow to another of your children.
Preimplantation Genetic Screening (PGS)
PGS tests for the correct number of chromosomes in the embryo. Chromosomal abnormalities cause the majority of failures to implant in IVF treatment and of miscarriages. Too many or too few chromosomes also cause diseases such as Down syndrome or Edwards syndrome. PGS also tests for translocations, a condition where the embryo may have the correct number of chromosomes but they are arranged incorrectly.
Chromosomal abnormalities in embryos are common even in young women, and they increase as women get older. Over age 40, 70 to 90 percent of a woman’s embryos will have chromosomal abnormalities due to the age of her eggs. If you have had recurrent miscarriages, failed IVF cycles, or unexplained infertility, or if you are age 35 or older, your fertility specialist may recommend PGS. PGS also identifies the sex of an embryo, so it may be used for family balancing or to select healthy embryos which will not carry a sex-based genetic defect, such as Jacobs syndrome or Klinefelter syndrome.
It’s important to remember that many syndromes and birth defects are not genetically linked, so genetic testing cannot discover them. But there are many diseases and abnormalities which PGD and PGS can identify.
Increasing Your Chances of a Healthy Baby
In IVF, all embryos are visually inspected by a trained embryologist and given a grade, based on the number and arrangement of cells and other criteria. But genetic defects aren’t visible to the eye, so embryos that appear to be healthy may in fact be poor quality. Genetic testing allows your reproductive endocrinologist to transfer healthier embryos, increasing your chance that the embryo will implant and decreasing your odds of miscarriage. A recent study found that implantation rates increased by 23 percent when using embryos whose quality was confirmed by genetic testing. Some fertility centers are transferring fewer embryos, in some cases only one, because higher quality embryos are more likely to implant, so fewer embryos are needed to result in a pregnancy. Single-embryo transfer greatly decreases your chance of twins or high-order multiples like triplets.