Cytogenetics: Advanced prenatal diagnosis for inherited diseases

Cytogenetics: Advanced prenatal diagnosis for inherited diseases

Prenatal diagnostic testing involves testing the baby before birth to spot certain abnormalities, including critical hereditary or spontaneous genetic disorders.

Ultrasonography and blood tests are safe and help doctors determine whether the couple will have to undergo advanced prenatal genetic tests like chorionic villus sampling, amniocentesis, and non-invasive umbilical blood sampling. Usually, doctors recommend these extensive tests when the baby in the womb is prone to genetic abnormalities such as a neural tube defect or a chromosomal abnormality. The chances of passing on the genetic abnormality are particularly higher when the woman is 35 or older.

Advanced science offers yet another diagnostic procedure called Pre-implantation genetic diagnosis (PGD) for couples with a history of genetic abnormalities. PGD is an ideal breakthrough if you are at an increased risk of having a baby with a genetic disorder. This procedure involves testing of embryos for genetic disorders and mutations before the embryologist transfers one into the uterus. Your doctor or embryologist will transfer only embryos that do not test positive for the disorders.

Doctors suggest specific tests for pregnant women during their 1st trimester to evaluate risk of genetic disorders in the foetus. 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. Sometimes women may need to undergo genetic screening tests during the second trimester as well. Information from these screening tests help us 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. You may require any of these techniques during specific time during the pregnancy for better outcomes in assisted conception.

 Types of prenatal diagnosis 

Ultrasonography

This is a non-invasive procedure that is harmless to both the foetus and the mother. Although an ultrasound examination can be quite useful to determine the size and position of the foetus and placenta, the amount of amniotic fluid, and the appearance of fetal anatomy, there are limitations to this procedure. Under rare situations, this test may not be able to detect subtle abnormalities until later in pregnancy, or after birth.

Amniocentesis

An invasive procedure involving extraction of amniotic fluid from the amniotic cavity inside the uterus through the mother’s lower abdomen. For couples who may have to undergo prenatal diagnosis, most obstetricians prefer carrying out amniocentesis between 14-20 weeks gestation. However, before extraction, you may have to undergo an ultrasound scan to know the gestational age, the position of the baby and placenta. It also helps to determine if enough amniotic fluid is present in the amniotic sac. 

Chorionic villus sampling (CVS)

CVS is a diagnostic test that can confirm whether or not your baby has any genetic abnormalities. This involves removing and testing a small sample of cells from the placenta (organ that supplies blood to the foetus). This test is only offered if the baby is at high risk of any chromosomal condition or disorder. Your obstetrician or gynaecologist may ask you to undergo CVS between the 11th and 14th week of pregnancy. In rare circumstances, your obstetrician may suggest this test again in the later stages of pregnancy, 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. Usually, a specially trained perinatologist, who specializes in foetal care in high-risk pregnancies, does a fetal blood sampling. It is done as part of diagnosing, treating, and monitoring fetal problems at various times during pregnancy. 

Genetic Sonogram

Genetic sonogram involves diagnosing foetal anomalies using ultrasound, anomaly scans and foetal echocardiography. Your doctor usually takes you through this test during 15 to 22 weeks of 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.

Why choose PGD?

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 the disease and its risk. They also have the opportunity to discuss their reproductive options with their physician. These options include testing for the disease when already pregnant. During an IVF cycle, pre-implantation genetic diagnosis (PGD) is done for screening embryos prior to implantation of the embryo. IVF with PGD helps in identifying and selecting only healthy embryos for implantation prior to pregnancy.

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.

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