What is Prenatal Genetic Screening? - Early Genetic Defect Detection

What is Prenatal Genetic Screening? - Early Genetic Defect Detection

Prenatal genetic screening is a useful tool to identify and diagnose genetic abnormalities in an unborn child. Your doctor may recommend genetic testing during pregnancy if you or your partner have a family history of genetic disorders. The tests are non-invasive and carry no associated risk.  The tests screen for abnormal chromosome numbers, likelihood of inheriting genetic disorders from the parent, and developmental abnormalities in the womb. Some tests can be performed on the potential parents before pregnancy, and some tests are performed in the first and second trimester of pregnancy. Prenatal genetic screening is recommended to pregnant women above 35, and couples who have a family history of genetic disorders. Pregnancies conceived through IVF are also recommended for prenatal genetic screening.

There are more than 1,000 chromosomal abnormalities that medical science has recorded. Prenatal genetic screening is a blanket term that covers a panel of tests to diagnose genetic abnormalities and potential future illnesses in the unborn child. Your obstetrician may recommend genetic testing during pregnancy if you or your partner have a family history of genetic disorders, or if you have a previous child with genetic disorders. The tests are non-invasive, and provide reliable, accurate information. An examination of the pregnant mother’s blood can give us a lot of information about the baby. The test can detect chromosomal abnormalities in the baby, such as a missing chromosome or an extra chromosome. It can also tell us whether the mother is at risk of carrying a baby with Down syndrome. Ultrasound tests are also more advanced, giving us the ability to accurately collect data on birth defects during the pregnancy.

Irregular results on a prenatal genetic screening does not necessarily mean your child has a genetic disorder. However, it is an indication that further diagnostic investigations need to be done. For further diagnostics, sample cells from the placenta, the amniotic sac or the umbilical cord must be tested. Prenatal genetic screening is a risk-free procedure for both pregnant mother and unborn child. Some diagnostic tests have been associated with risk of infection, bleeding and miscarriage.

Women who are currently pregnant or plan to get pregnant shortly can opt for prenatal genetic screening. Prenatal genetic counselling is particularly important for:

– Women above 35 who are pregnant or considering having a child

– Women who have a close relative with developmental delays or birth defects

– Women whose partners have a close relative with developmental delays or birth defects

– Pregnancies conceived through IVF

– Women who have had multiple unexplained miscarriages

– Women who have a previous child with a genetic disorder

– Women who have been exposed to medications, infections or any other hazards during pregnancy.

Screening tests are not diagnostic in nature, i.e. they do not confirm an abnormality in the foetus. Screening tests only indicate that there is a higher risk of genetic disorders. Your doctor will interpret the results of the screening tests and advise you to go for further diagnostic tests if they feel it is necessary. Some of the common prenatal genetic screening tests are:

Carrier screening – These are blood tests conducted on both parents. They will identify small changes in the parents’ genetic code that could increase the risk of the baby having a genetic disease, such as cystic fibrosis, sickle cell anaemia or spinal muscular atrophy. If both parents are carriers of the same genetic risk, the baby may have a more serious susceptibility to the disease. Usually the diseases tested for are single-gene conditions, i.e. diseases triggered by an abnormality in a single gene. These tests can be performed at any time during the pregnancy or even before the pregnancy.

Abnormal chromosome number – Chromosomes are inherited in pairs – Each pair has a chromosome from each parent. Sometimes during fertilisation, issues can arise. The foetus may end up with too many pairs, too few pairs or missing portions of certain chromosomes. This can cause genetic disorders like Down syndrome or Turner’s syndrome. The chromosome number can be detected using a cell-free fetal DNA screening. The foetus’s DNA is present in very small amounts in the mother’s blood after 10 weeks into the pregnancy. This DNA is isolated from the mother’s blood and tested.

Screening for Physical abnormalities – During pregnancy, the mother goes through periodic ultra-sound scans to make sure the baby is healthily developing inside the uterus. The ultrasound will look at key indicators like the baby’s heart development, skeleton, eyes, kidneys, arms and legs. This is done throughout the pregnancy but is crucial during the second trimester. The mother will also undergo blood tests like AFP screening. High levels of AFP in the mother’s blood may indicate problems in the physical development of the baby’s face, spine or abdomen.

Genetic counselling is a reliable way to understand how genetic disorders can affect the unborn child. The genetic counsellor is a doctor who interprets your prenatal genetic screening test results and your family medical histories to give you a picture of the potential risks your child faces. The genetic counsellor supports the couple through the testing process, and helps them decide what is right for them. They advise them on the degree of risk to be expected. Some couples choose to not act on the results of the screening, and wait until after birth to consider their options. Some couples also choose to go for further diagnostic tests, fetal surgery or in extreme cases, termination of the pregnancy.

The timing of the tests depends on the nature of the tests being performed. It is advisable to meet with a genetic counsellor early in the pregnancy, and conduct the tests at the time advised by the obstetrician. Carrier screening tests can be done at any point of time in the pregnancy. Cell-free fetal DNA screening is done after 10 weeks of pregnancy. First trimester screening is done between 11-14 weeks of pregnancy.

Prenatal screening tests are not perfect, but they are reasonably accurate. As with any type of testing, false positives and false negatives are possible. The screening test result is to be interpreted as an indicator of high risk, and not a confirmed diagnosis.

The non-invasive components of prenatal genetic testing, like the ultrasound tests and the NIPT panel, have virtually no risk. The results of these tests may require further investigation. In such case, when invasive tests like CVS (Chorionic Villus Sampling) or Amniocentesis are performed, there is a small risk of developing complications. The most common complications are minor bleeding, infection and leakage of amniotic fluid, physical injury to the baby, and miscarriage. The risk of miscarriage is notable low though (less than 1%).

If a genetic abnormality is detected, the parents are presented with several options:

-Further diagnostic tests to confirm or negate the results.

-Genetic counselling to understand the implications of the results.

-Decision-making regarding how to proceed with the pregnancy, vis a vis special care, medical interventions etc.

Each case is unique in this regard. The doctors are the best source of correct information on which to base your decisions.

For expert guidance and support regarding prenatal genetic screening, consult the specialists at Kauvery Hospital. With branches in Chennai, Hosur, Salem, Tirunelveli, and Trichy, our team is dedicated to providing comprehensive care and information to help you make informed decisions during your pregnancy. Contact us today to learn more about our services and schedule your consultation.

What is prenatal genetic screening?
It’s a set of non-invasive tests during pregnancy that checks for genetic abnormalities and potential disorders in the unborn child.

Who should consider prenatal genetic screening?
It’s recommended for pregnant women over 35, those with a family history of genetic disorders, IVF pregnancies, or with unexplained miscarriages.

What types of prenatal screening tests are available?
Common tests include carrier screening, cell-free fetal DNA tests, first trimester screenings, and ultrasound exams.

How accurate are these screening tests?
They are reasonably accurate but serve as indicators; abnormal results usually need further diagnostic tests for confirmation.

Are there any risks with prenatal genetic screening?
Non-invasive tests carry virtually no risk, but invasive tests like amniocentesis have a very small risk of complications.

What happens if an abnormality is detected?
Your doctor will advise further diagnostic testing and provide genetic counselling to help you understand your options.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai (Alwarpet & Vadapalani), Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

Chennai Alwarpet – 044 4000 6000 •  Chennai Vadapalani – 044 4000 6000 • Trichy – Cantonment – 0431 4077777 • Trichy – Heartcity – 0431 4003500 • Trichy – Tennur – 0431 4022555 • Hosur – 04344 272727 • Salem – 0427 2677777 • Tirunelveli – 0462 4006000 • Bengaluru – 080 6801 6801