Cytogenetics: Advanced prenatal diagnosis for inherited diseases
Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic disorders.
Ultrasonography and blood tests are safe and now-a-days they also help in determining whether advanced prenatal genetic tests like chorionic villus sampling, amniocentesis, and percutaneous umbilical blood sampling are needed. Usually, these more invasive tests are done when couples have an increased risk of having a baby with a genetic abnormality such as a neural tube defect or a chromosomal abnormality, particularly when the woman is 35 or older.
Yet another diagnostic procedure termed as Pre-implantation genetic diagnosis (PGD) may be offered to couples who are using IVF (in vitro fertilization) to become pregnant and who are at increased risk of having a baby with a genetic or chromosomal disorder. Before an embryo is transferred to a woman’s uterus, it is tested for certain genetic disorders and mutations. Only embryos that do not test positive for the disorders are transferred.
Women are customarily offered a variety of genetic screening tests during their first trimester of pregnancy to evaluate the risk for genetic disorders for their unborn baby. The first trimester screening tests are usually carried out between the 10th and 13th week of pregnancy. They involve measuring the level of certain substances in the mother’s blood and obtaining an ultrasound. Genetic screening tests can be done during the second trimester as well. Information from these screening tests are used to help determine even the slightest possibility that the fetus might be born with genetic disorders such as Down syndrome, cystic fibrosis, Tay-Sachs disease, sickle cell anaemia, etc.
There are a variety of non-invasive and invasive techniques available for prenatal diagnosis. Each of them can be applied only during specific time periods during the pregnancy for greatest utility. The techniques employed for prenatal diagnosis include:
- Chorionic villus sampling
- Fetal Blood Sampling
- Genetic Sonogram
This is a non-invasive procedure that is harmless to both the fetus and the mother. Although an ultrasound examination can be quite useful to determine the size and position of the fetus, the size and position of the placenta, the amount of amniotic fluid, and the appearance of fetal anatomy, there are limitations to this procedure. Subtle abnormalities may not be detected until later in pregnancy, or may not be detected at all.
This is an invasive procedure which involves passing a needle through the mother’s lower abdomen into the amniotic cavity inside the uterus. For prenatal diagnosis, most amniocenteses are performed between 14 and 20 weeks gestation. However, an ultrasound examination is always carried out before amniocentesis in order to determine gestational age, the position of the fetus and placenta, and determine if enough amniotic fluid is present.
Chorionic villus sampling (CVS):
CVS is a diagnostic test that can confirm whether or not your baby has any genetic abnormalities. It involves removing and testing a small sample of cells from the placenta (the organ linking the mother’s blood supply to her unborn baby). It is only offered if there’s a high risk your baby could have a genetic or chromosomal condition. It is usually carried out between the 11th and 14th weeks of pregnancy, although it’s sometimes performed later than this if necessary.
Fetal Blood Sampling:
This involves collecting of fetal blood directly from the umbilical cord or fetus. The fetal blood is tested for signs of anaemia and other blood problems. Fetal blood sampling is usually done by a specially trained perinatologist, a doctor who specializes in the care of the fetus in high-risk pregnancies. It is done as part of diagnosing, treating, and monitoring fetal problems at various times during pregnancy.
This involves diagnosing foetal anomalies using ultrasound, anomaly scans and foetal echocardiography. It is performed at 15 to 22 weeks into the pregnancy. This ultrasound scan includes an examination of the developing fetus, the uterus, placenta, cervix and the regions of the ovaries. This screening aims to identify more than 75 percent of major structural malformations by 22 weeks.
If a couple knows prior to pregnancy that they carry a genetic mutation that could lead to a significant disease in their child, they have the opportunity to learn about their risk and the disease prior to pregnancy. They also have the opportunity to discuss their reproductive options with their physician. These options include testing for the disease when already pregnant or testing embryos prior to pregnancy via IVF with preimplantation genetic diagnosis (PGD). IVF with PGD allows couples to test embryos for genetic diseases prior to becoming pregnant and to select only healthy embryos for implantation.
At Milann, we have been offering genetic screening to all of our patients for many years and have thus helped numerous couples achieve healthy pregnancies. We urge women who are considering pregnancy in the future to reach out to our specialists and discuss screening options.