Antenatal Screening and Counselling
What are Birth Defects?
Birth defects are structural or functional abnormalities that are present at birth. These defects occur while a baby is developing in the mother's body. Some of these are clinically obvious at birth, however, a few get diagnosed much later in life.
What are the Screening Tests Ordered during Pregnancy?
Screening tests help to know about a pregnant woman's risk of having a baby with certain birth defects. These are done during the first and second trimesters of pregnancy.
First trimester screening tests
Screening tests in the first trimester are done between 11 and 14 weeks and include blood tests and ultrasound scans to detect the risk of Down syndrome and Trisomy 18. These results, along with the mother's age, detect Down syndrome in approximately 82-87% of the cases.
Second trimester screening tests
Screening tests in the second trimester are usually performed between 15 and 20 weeks. They involve detecting a protein and three particular hormones. The presence of these hormones alone indicates Down syndrome in 69% of the cases, and detecting all four (the protein and the three hormones) indicates Down syndrome in 81% of the cases.
Also, neural tube defects can be predicted in a good number of cases if the protein is detected in the blood.
The tests of the first and second trimester screenings can be combined to confirm birth defects such as Down syndrome in a relatively larger number (90-95%) of the cases. Positive screening tests are usually followed by diagnostic tests for further information.
Counselling for Birth Defects
Early pregnancy genetic counselling involves counselling a pregnant woman about her chances of having a child with a genetic disorder or birth defect as well as the different testing and treatment options available. Specially trained genetic counsellors provide information which helps to identify families at risk of genetic diseases and risks associated with specific chromosomal and foetal abnormalities.
Relevant genetic tests are ordered after reviewing the family history and medical records. The counsellor interprets the technical and scientific information of the genetic test results to the parents. The parents can then make informed decisions in consultation with their counsellor.
Candidates for Prenatal Genetic Counselling
It is always advisable to seek genetic counselling when planning for pregnancy. However, a meeting with the genetic counsellor after becoming pregnant is also helpful to minimise potential risks. Prenatal genetic counselling becomes all the more important for candidates:
- 33 years and older
- With a family history of any genetic disorder
- With abnormal ultrasound or blood test results
- Exposed to certain medications during pregnancy
- Affected with any infections during pregnancy
- Whose previous pregnancies were translated into miscarriages
- Who are infertile