Genetic Counseling
Genetic Counseling
Genetic counseling
Genetic counseling is the information provided by the counselor as to how certain genetic disease might affect you and your family and what is the risk of transmission to your children. The doctor will first collect your and family history.
It is done in those cases-
- If There Is Family History Of Hereditary Disease In Your Family
- if There Is History Of Affection Of Birth Defect Or Genetic Disease In The Previous Child
- If There Is History Of Certain Findings On Ultrasound In The Present Pregnancy Which Can Point Towards A Genetic Disorder.
- Abnormal Screening Results Or Invasive Testing Results
After counseling, a repeat scan or certain tests might be prescribed.
What does the genetic test involve?
Genetic tests usually involve extracting a placental sample(CVS), amniotic fluid (Amniocentesis) or a blood sample (Fetal blood sampling) from the baby by an invasive testing and the material is sent to the laboratory for further analysis.
What is a genetic condition?
Genetic conditions are problems that can occur either because of a problem with the chromosomes such as Down’s syndrome, or with the individual genes for example, beta thalassemia.
What causes genetic disorders?
A genetic disorder can happen if the parents carry the defective genes(carriers) and pass on to their babies or when a defect in the gene occurs in the baby alone for unknown reasons
NIPT-non invasive prenatal testing
Prenatal screening for trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), and selected sex chromosome aneuploidies can be performed using next-generation sequencing of cell-free DNA (cfDNA) in maternal blood. This is possible because cfDNA from the fetal-placental unit can be detected in maternal blood as early as five weeks of gestation and is completely cleared from maternal blood soon after delivery
Why is NIPT performed?
NIPT- Non invasive prenatal testing is a blood test performed for the expectant mother, a relatively new modality of screening for common chromosomal abnormalities in pregnancy.
In this test, the mothers blood sample is taken and the baby’s chromosomes (genetic material) are looked for using advanced DNA technology. The test is based on the fact that the genetic material- the DNA, from the placenta is shed into the mothers blood circulation. The placenta has the same chromosomal make up as that of the baby and testing the placental genetic material would reflect the baby’s genetic material. So, let’s get answers for some commonly asked questions about NIPT.
What are chromosomes and chromosomal abnormalities?
The genetic material in the cells of our body are responsible for the structure and functioning of the body. This genetic material is organised into 46 units called chromosomes. Of the 46, 23 comes from the egg(mother) and 23 from the sperm(father).
Sometimes, due to various reasons, there can be additional chromosomes. Most commonly, the additional chromosome is either the 21st, 18th or 13th chromosome. Addition of an extra chromosome is called trisomy. Trisomy 21 is called Down syndrome. Trisomy 18 is called Edwards syndrome, trisomy 13 is called Patau syndrome. So the baby has 47 chromosomes instead of 46. This leads to abnormal structure and functioning of the body.
What is Down’s syndrome?
The most common chromosomal abnormality, the Down’s syndrome is caused due to 3 copies of chromosome 21 rather than the usual 2 copies. It can lead to various degree of structural problems in various organs like heart, intestine, brain and varying degree of learning disability.
What is Edwards syndrome?
Edwards syndrome is caused due to 3 copies of chromosome 18 rather than the usual 2. It causes severe intellectual disability, structural problems of the heart, small head and jaw, clenched fist, to name a few. Most babies with Edwards syndrome die before birth or within a few weeks after birth.
What is Patau syndrome?
Patau syndrome is caused due to 3 copies of chromosome 13 rather than the usual 2. It causes severe structural problems. It causes severe growth restriction for the baby, abnormal structure of brain, small eyes, cleft in the lip and palate, low tone of the muscles, abdominal wall defects to name a few.
What is the commonly used screening modality for the common chromosomal abnormalities?
The commonly used screening is called the combined screening which is a combination of ultrasound scan of the developing baby and blood test for the expectant mother. The risk for chromosomal abnormalities is assessed which could be Low risk, Intermediate risk or high risk.
Can one get a NIPT instead of combined screening?
The answer is NO*. The NIPT checks only for the three common chromosomes namely the 21st, 18th and 13th chromosomes. There are several structural abnormalities that occur without any chromosomal abnormalities, few others occur due to genetic abnormalities not detectable by NIPT. Therefore, it is important to have scan at 11-13 weeks, that can detect structural abnormalities in the baby. The scan also provides an opportunity to assess the risk of developing high blood pressure in the coming weeks of pregnancy.
So, who should get the NIPT test done?
1. One can get the NIPT test done in addition to the scan when the scan is normal with intermediate risk for chromosomal abnormality and if one is not sufficiently reassured about the risk. The detection rates of Down’s syndrome with combined screening is about 90-92 percent and for NIPT is 99 percent.
2. When the risk for downs syndromes shows high risk without any structural abnormalities* in the fetus.
When a structural abnormality is detected on scan and is suspected be due to chromosomal defect, can NIPT be performed to confirm this?
When a structural anomaly is detected, Karyotyping of the chromosomes is recommended, which looks into all the 46 chromosomes and not just the three common ones. In addition, a chromosomal microarray test could be performed to detect submicroscopic changes in the chromosomes. This would be possible by performing an amniocentesis and performing a Karyotype and microarray. In fetuses with structural abnormalities, only 70% of the chromosomal abnormalities are caused due to the common trisomies 21, 18 and 13. Therefore, performance of detailed genetic tests like chromosomal microarray* after amniocentesis could add more clinically relevant genetic information in these fetuses.
Can NIPT be performed in twins?
Yes** it can be performed to screen for trisomy 21( Down syndrome). Studies have shown that the accuracy of the NIPT in twin pregnancy is similar to singleton pregnancies for screening for Down syndrome. If the NIPT shows low risk, it is reassuring as the detection rates for Down’s syndrome is about 99 percent. If NIPT shows high risk, confirmatory test ( CVS/ amniocentesis) needs to be performed for both the twins to accurately determine which of the twins or if both the twins are affected.
Currently there is insufficient evidence for screening for Edward syndrome and Patau syndrome in twin pregnancy.
Can NIPT be performed in triplets?
Currently there is insufficient evidence for use of NIPT as screening tool for common trisomies in triplet pregnancy.
How is NIPT performed?
About 5 ml of blood is withdrawn from mother. The sample is sent for testing for the lab. The results are available within 10 days. The results of the test are expressed as either high risk, where the chance of baby having chromosomal problem is high or low risk where the chance of baby having chromosomal problem is low.
If the NIPT shows high risk does that mean that baby really has chromosomal abnormality?
***Once, high risk on NIPT for Down’s syndrome, the probability of that baby really has Down’s syndrome is about 91 percent and the other 9 percent could be normal.
Once, high risk on NIPT for Edwards syndrome, the probability of that baby really has Down’s syndrome is 84 percent.
Once, high risk on NIPT for Patau syndrome, the probability of that baby really has Down’s syndrome is 87 percent.
This is the reason why confirmatory diagnostic tests- either a chorionic villus sampling ( CVS) or amniocentesis needs to be performed.
Low risk on NIPT, what next?
When the fetus has no structural abnormalities and the result on NIPT is low risk, then the probability of baby having chromosomal abnormality is very low, therefore it’s reassuring for the couple and treating Doctors.