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Prenatal Testing
Why is prenatal testing done?
Prenatal testing is offered to women during pregnancy to determine if the fetus has a possibility to be born with a genetic condition or birth defect. Performing prenatal testing may be important to women who might want to explore who know their babies are already at risk and want to make the best decisions for better outcome of their baby. Different prenatal testing options are available according to the trimester that the mother is in.
So, who is prenatal testing offered to?
Even though prenatal testing is offered to all women, as the age of a mother increases, the chances of having a baby with chromosomal abnormality increases. So, the age of a mother is the most common reason for prenatal testing. Family history or a previous child with a genetic condition, parents who are known carriers of a specific genetic mutation, abnormal ultrasound findings and screening tests are some other reasons that women may be offered screening tests.
Remember screening tests are not "diagnostic (disease proving)"
Screening tests only identify women who have an increased chance of having a baby, with certain chromosomal abnormalities. They dont "identify" birth defects such as genetic diseases. Results that reveal levels over a "cut-off" are called positive results and these women then undergo further testing. These tests are able to screen many cases at risk but please note, that these too can miss a high risk case where the woman may get a "negative screening" result.
Another type of testing is diagnostic testing, it can determine exactly if the fetus/baby has a certain genetic condition or birth defect.
Screening Tests
An ultrasound and a mother's blood test sample.
An ultrasound in the first trimester is done around 6-9 weeks to confirm pregnancy, estimate the gestational age (baby's age), and check for the presence of a fetal heartbeat. This ultrasound may be repeated in the first trimester to perform a nuchal-translucency scan. This test is done between 11 and 14 weeks of pregnancy. It measures the thickness of the fluid buildup at the back of the baby's neck (nuchal fold) to screen for certain chromosomal abnormalities, such as Down Syndrome.
The blood test measures the levels of two pregnancy-related substances: Pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG). Maternal blood tests are also conducted as part of routine prenatal care. They assess various factors, such as blood type, Rh factor, hemoglobin levels, immunity to certain factors (e.g Rubella), and may screen for conditions like anemia (low blood cell count) or gestaional diabetes (diabetes in pregnancy).
Cell-Free DNA Testing (cfDNA): This is a non-invasive prenatal screening test is offered to assess the risk of chromosomal abnormalities, including Down syndrome (Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21, resulting in intellectual and developmental delays, distinctive facial features, and potential health concerns), trisomy 18 (Edwards syndrome, is a chromosomal disorder characterized by the presence of an extra copy of chromosome 18, leading to severe developmental and medical complications), trisomy 13 (Patau syndrome, is a chromosomal disorder caused by an extra copy of chromosome 13, resulting in significant intellectual and physical disabilities). It involves analyzing the fragments in the mother's blood. cfDNA testing is usually offered around 10 weeks later in the first trimester.
The results of the ultrasound, Nuchal Translucency Measurement, and blood test are used together to assess the risk of chromosomal abnormalities.
Mother's blood sample only. This includes Quad Marker Screening: this blood test is usually performed between 15 and 20 weeks. It measures markers including alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin-A.
Anatomy Ultrasound also knows as fetal anomaly scan is performed between 18 and 22 weeks of pregnancy. It examines the baby's anatomy, including the organs, limbs, spine and brain to identify and structural abnormalities.
Glucose Challenge Test (GCT) is a test done to screen gestational diabetes (diabetes during pregnancy). It involves drinking a glucose solution followed by a blood test to measure blood sugar levels at a specific time.
Antibody Screening: This blood test checks for the presence of antibodies in the mother's blood that may indicate potential risks for baby, such as Rh sensitization (Rh incompatibility) or other blood-related conditions.
Group B Streptococcus (GBS) Screening: This test is typically performed around 35 to 37 weeks of pregnancy. It involves taking a swab from the vagina and rectum to check for the presence of Group B Streptococcus bacteria, which can cause infections in newborn during delivery.
