Let us know about Screening and tests during pregnancy to detect birth defects. After becoming pregnant, many questions may arise in a woman’s mind, such as whether the child will be okay? You may be more concerned if there is a family history of chromosomal abnormalities or if you are over the age of 35. This leads you to the obvious question: How to find out about birth defects during pregnancy?
However, the good news is that this is possible in two ways: screening and diagnostic tests.
Why is screening done during pregnancy for birth defects?
Prenatal screening is done to check whether the fetus is at risk of developing any genetic abnormalities. These tests are non-invasive and do not take much time to perform. Diagnostic tests, on the other hand, involve some risks and are invasive, making screening the first route for diagnosis. If the result is positive, diagnostic tests are considered to confirm the birth defect.
pregnancy screening test
Screening tests are done during the first and second trimester of pregnancy .
in the first quarter
The test is done during the first trimester between weeks 9 and 13 . These tests include:
1 . Blood test
You will need to undergo a simple blood test which will analyze the components like free B-HCG and PAPP-A (plasma protein A) in your blood. Both of these are biochemical markers that provide information about the fetus’s risk for Down syndrome , Patau syndrome, and Edwards syndrome .
2 . Nuchal Transparency
In this test , ultrasound is done to check the collection of fluid behind the neck of the fetus. The increased thickness means the fetus is at risk for trisomy 21 and other genetic abnormalities. Studies have shown that this method of screening has only an 80 percent detection rate and a five percent chance of false positives. If the blood test mentioned above is done then it increases to 90 percent.
The above tests not only help detect genetic abnormalities but also predict other pregnancy-related problems. For example, low PAPP-A in the mother, pre-eclampsia , death of the baby and problems with intrauterine growth.
in the second quarter
A number of tests are done together during the second trimester and are collectively known as quad marker tests . It measures the levels of four biomarkers that help show the risk of chromosomal abnormalities in the fetus. This test is done during the second trimester between the 14th and 18th weeks . However, it can be done even till the 22nd week .
1 . Alpha-fetoprotein
It analyzes the presence of a plasma protein that is produced in the fetal liver, known as alpha-fetoprotein (AFP) . Women with high levels of the protein are more likely to have children with neural defects such as spina bifida and anencephaly. On the other hand, women with low levels of AFP have a higher risk of having a baby with Down syndrome. However, this test should be done along with other tests to get an accurate information.
2 . Human Chorionic Gonadotropin
It originates in the placenta . Women who have increased levels are more likely to have children with Down syndrome.
3 .Estriol
This is a type of estrogen that is produced by both the fetus and the placenta. Abnormal levels in the test mean that the fetus has an increased risk of having Down syndrome, Edwards syndrome, or some other genetic abnormality.
4. Inhibin-A
It is a hormone found in the placenta. Studies have shown that the detection rate of Down syndrome and other chromosomal abnormalities has been dramatically improved by measuring this hormone. You can get the first and second trimester tests done together, which is known as an integrated screening test.
Pregnancy Diagnostic Tests
Birth defects are diagnosed by the process of elimination. Although the screening process is now over, there is always a possibility of getting a false positive result. Furthermore, diagnostic tests are usually invasive and in some cases even risky. This is why diagnostic tests are only done when screening tests indicate moderate to high risk.
in the first quarter
How can birth defects be detected early? This is a very good question. The tests mentioned below are planned between the 10th and 13th week of pregnancy and this is the earliest time when you can definitely detect birth defects.
1 . Chorionic villus sampling
For this test, a sample of chorionic villus is taken which is found in the placenta. It is similar to a projection in the placenta and is different because it contains the same genes as the fetus. It is used to detect chromosomal abnormalities such as Down syndrome or cystic fibrosis. However, it does not help in detecting neural tube defects. Some of the risks associated with this diagnostic test include miscarriage , infection, or defects in the baby’s feet and fingers. This test is absolutely accurate but sometimes shows false-positive results. Furthermore, the results are sometimes unclear, and amniocentesis is needed for further clarification. The timing of results may vary and may take a few days or even a few weeks.
in the second quarter
While chorionic villus sampling is one way to go about this, it cannot detect all birth defects. Additionally, if your uterus is tilted backward and the placenta is also located behind the uterus, a chorionic test is considered. Finally, if your screening is positive after 13 weeks, you can try the tests below. While amniocentesis is done between the 15th and 18th weeks, ultrasound is done between the 18th and 20th weeks .
1. Amniocentesis
Amniotic fluid contains a substance called alpha-fetoprotein or AFP. A needle is inserted into the uterus through the abdomen. Now, less than thirty milliliters of amniotic fluid that surrounds the fetus is removed and analyzed. This test is useful in detecting Down syndrome, muscular dystrophy, spina bifida, and sickle cell disease. It has an accuracy rate of 99.4 percent, and 1 in 200 women are at risk of miscarriage after taking the test. You will get results within three weeks.
2 . Level 2 Ultrasound
This form of ultrasound is similar to a regular ultrasound, but the results are more targeted. The focus is on specific sites such as the brain, heart and other organs. It is used to detect Down syndrome and is non-invasive, unlike amniocentesis and chorionic villus sampling. The result is available after the ultrasound is completed.
Amniocentesis and chorionic villus sampling are both invasive and you are not allowed to do any vigorous exercise for at least a few days after the test.
It is your choice to get any test done. However, most obstetricians say that it is better to do the test so that the fear and worry about birth defects during pregnancy goes away from your mind.
