Pregnant women undergo screening tests during the first and the second trimester to detect any birth defects or genetic disorders in the foetus. To detect birth defects during pregnancy, screening tests are performed based on the stages of pregnancy. Pre natal tests rarely miss any birth defect making it a reliable diagnostic tool for doctors to rely upon.
First Trimester Screening
The screening during the early stages of the pregnancy is a combination of diagnostic tests between the 11th and the 13th week of the pregnancy. It checks for birth defects related to the heart or chromosomal disorders such as Down syndrome. It includes a blood tests and an ultrasound.
- Maternal Blood Screen is a basic blood test that gauges the protein levels in the body. This test usually traces two proteins human chorionic gonadotropin (hCG) and pregnancy associated plasma protein. If the protein levels are too low or too high, it may signify chromosomal aberration in the foetus.
- Ultrasound uses high frequency sound waves to form an image of the foetus on the screen. The ultrasound can determine the due date, determine causes of bleeding if at all, monitor the overall development of the foetus, measure the amniotic fluid, check the condition of the placenta that supplies nutrients for the survival of the foetus and determine the sex of the foetus. Sex determination is illegal in many countries.
- Chronic Villi Sampling is performed up to the 12th week of pregnancy. CVS can determine genetic abnormalities. A catheter or needle is inserted into the womb and chronic villi are extracted. The chronic villi contain the same DNA as the foetus. This test is relatively safe but if not performed with precision and skill, it may lead to a miscarriage. Some studies state that the test itself may be responsible for limb deformities in the foetus. Ensure you consult with your doctor for a safe CVS.
Second Trimester Screening
The second trimester screening is completed between 15 to 18 weeks of pregnancy. The diagnostics tests for birth defects during pregnancy include maternal serum screening, anomaly ultrasound and amniocentesis.
- Maternal Serum Screening is a blood test conducted to check if the foetus has birth defects like chromosomal disorders, neural tube defects. It is commonly called the triple screen test or a quad screen test depending on the number of proteins the mother is tested for.
- Anomaly Ultrasound is recommended after the foetus has completed 18 to 20 weeks of pregnancy. The ultrasound checks for the size, position and development of the baby along with detecting birth defects.
- Amniocentesis is a test where a sample of the amniotic fluid is collected from the embryo sack. The fluid is then tested to check for protein levels in the baby, a fluctuation will signify a possible birth defect or genetic problems such as Tay-Sachs disease or cystic fibrosis. Amniocentesis is suggested to women who have received an abnormal result in other screening procedures.
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