I believe most of the moms to be are worry about health of their unborn child. We are lucky nowadays to have some opportunities to do genetic and other screenings and discover if your baby might have a risks for genetic disorders.
On my post I would like to tell you some information about available tests.
What is genetic screening?
Many genetic abnormalities can be diagnosed before birth. Your doctor or midwife may recommend genetic testing during the pregnancy if you or your partner have a family history of genetic disorders and/or you have had a fetus or baby with a genetic abnormality.
Examples of genetic disorders that can be diagnosed before birth include the following:
- Cystic fibrosis
- Duchenne muscular dystrophy
- Hemophilia A
- Sickle cell anemia
- Polycystic kidney disease
- Tay-Sachs disease
What do genetic screening methods include?
Genetic screening methods may include the following:
- Ultrasound scan
- Alpha-fetoprotein test (AFP) or multiple marker test
- Chorionic villus sampling (CVS)
- Percutaneous umbilical blood sampling (withdrawing a small sample of the fetal blood from the umbilical cord)
First Trimester Prenatal Screening Tests
First trimester screening is a combination of fetal ultrasound and maternal blood testing performed during the first trimester of pregnancy. This screening process can help to determine the risk of the fetus having certain birth defects. Screening tests may be used alone or in combination with other tests.
There are three parts of first trimester screening:
- Ultrasound test for fetal nuchal translucency (NT). Nuchal translucency screening uses an ultrasound test to examine the area at the back of the fetal neck for increased fluid or thickening.
- Two maternal serum (blood) tests. The blood tests measure two substances found in the blood of all pregnant women:
- Pregnancy-associated plasma protein screening (PAPP-A)–a protein produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality.
- Human chorionic gonadotropin (hCG)–a hormone produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality.
When used together as first trimester screening tests, nuchal translucency screening and maternal blood tests have a greater ability to determine if the fetus might have a birth defect, such as Down syndrome (trisomy 21) and trisomy 18.
If the results of these first trimester screening tests are abnormal, genetic counseling is recommended. Additional testing such as chorionic villus sampling, amniocentesis, cell-free fetal DNA, or other ultrasounds may be needed for accurate diagnosis.
After you have turned at least 9 weeks of your pregnancy you can have NON INVASIVE genetic tests performed by blood drawing labs in your health provider facility. One of the tests is – the “Panorama” is made for women of any age and ethnicity. It is not meant for women who are carrying more than one baby (twins or triplets), or for women who have used a donor egg, or have received a bone marrow transplant. Most women who have the Panorama screening test will find out their baby is at low risk for the conditions tested. This means that the chance of the baby having one of these conditions is very low, which can be reassuring. When the test result shows a high risk, it is important to talk with your healthcare provider about your next steps. One of the great benefits of this test is gender reveal if you would mention it before the test to your health provider. You can know who are you carry on in your womb around 10 weeks of your pregnancy. I have used this test and was pretty excited to know that we will have a girl. Check your medical insurance before screening to know if you are eligible for free test.
Second Trimester Prenatal Screening Tests
Second trimester prenatal screening may include several blood tests, called multiple markers. These markers provide information about a woman’s risk of having a baby with certain genetic conditions or birth defects. Screening is usually performed by taking a sample of the mother’s blood between the 15th and 20th weeks of pregnancy (16th to 18th is ideal). The multiple markers include:
- Alpha-fetoprotein screening (AFP). This blood test measures the level of alpha-fetoprotein in the mothers’ blood during pregnancy. AFP is a protein normally produced by the fetal liver and is present in the fluid surrounding the fetus (amniotic fluid), and crosses the placenta into the mother’s blood. The AFP blood test is also called MSAFP (maternal serum AFP).Abnormal levels of AFP may signal the following:
- Open neural tube defects (ONTD), such as spina bifida
- Down syndrome
- Other chromosomal abnormalities
- Defects in the abdominal wall of the fetus
- Twins–more than one fetus is making the protein
- A miscalculated due date, as the levels vary throughout pregnancy
- hCG. This is human chorionic gonadotropin hormone (a hormone produced by the placenta)
- Estriol. This is a hormone produced by the placenta
- Inhibin. This is a hormone produced by the placenta
Abnormal test results of AFP and other markers may indicate the need for additional testing. Usually an ultrasound is performed to confirm the dates of the pregnancy and to look at the fetal spine and other body parts for defects. An amniocentesis may be needed for accurate diagnosis.
Multiple marker screening is not diagnostic. This means it is not 100 percent accurate, and is only a screening test to determine who in the population should be offered additional testing for their pregnancy. There can be false-positive results–indicating a problem when the fetus is actually healthy or false negative results–indicating a normal result when the fetus actually does have a health problem.
When a woman has both first and second trimester screening tests performed, the ability of the tests to detect an abnormality is greater than using just one screening independently. Nearly all cases of Down Syndrome can be detected when both first and second trimester screening are used.
What is an amniocentesis?
An amniocentesis is a procedure used to obtain a small sample of the amniotic fluid that surrounds the fetus to diagnose chromosomal disorders and open neural tube defects (ONTDs), such as spina bifida. Testing is available for other genetic defects and disorders depending on the family history and availability of laboratory testing at the time of the procedure. An amniocentesis is generally offered to women between the 15th and 20th weeks of pregnancy who are at increased risk for chromosome abnormalities, such as women who are over age 35 years of age at delivery, or those who have had an abnormal maternal serum screening test, indicating an increased risk for a chromosomal abnormality or neural tube defect.
How is an amniocentesis performed?
An amniocentesis is a procedure that involves inserting a long, thin needle through the mother’s abdomen into the amniotic sac to withdraw a small sample of the amniotic fluid for examination. The amniotic fluid contains cells shed by the fetus, which contain genetic information.
Women with twins or other multiples need sampling from each amniotic sac, in order to study each baby. Depending on the position of the baby, placenta, amount of fluid, or patient’s anatomy, sometimes the amniocentesis cannot be performed. The fluid is sent to a genetics laboratory so that the cells can grow and be analyzed. Alpha-fetoprotein, a protein made by the fetus that is present in the fluid, is also measured to rule out an open neural tube defect, such as spina bifida. Results are usually available in about 10 days to two weeks, depending on the laboratory.
What is a chorionic villus sampling (CVS)?
Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of some of the placental tissue. This tissue contains the same genetic material as the fetus and can be tested for chromosomal abnormalities and some other genetic problems. Testing is available for other genetic defects and disorders depending on the family history and availability of laboratory testing at the time of the procedure. In comparison to amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test between 16 to 18 weeks of their pregnancy, to screen for neural tube defects.
How is CVS performed?
CVS may be offered to women who are at increased risk for chromosomal abnormalities or have a family history of a genetic defect that is testable from the placental tissue. CVS is usually performed between the 10th and 12th weeks of pregnancy. Although exact methods can vary, the procedure involves inserting a small tube called a catheter through a woman’s vagina and into her cervix.
Women with twins or other multiples usually need sampling from each placenta. However, because of the complexity of the procedure, and positioning of the placentas, CVS is not always feasible or successful with multiples.
California Prenatal Screening Program
I live in Northern California and found out that there is an option for future moms to do a genetic screening for $207.
- Quad Marker Screening – One blood specimen drawn at 15 weeks – 20 weeks of pregnancy (second trimester test).
- Serum Integrated Screening – Combines a first trimester blood test screening result (10 weeks-13 weeks 6 days) with a second trimester blood test screening result (15 weeks-20 weeks).
- Sequential Integrated Screening – Combines first and second blood test results with Nuchal Translucency (NT) ultrasound results. This type of ultrasound is done by clinicians with special training. It measures the back of the fetus’ neck. This measurement helps screen for Down syndrome (trisomy 21). (Note: the Screening Program does not pay for NT ultrasounds).
The Prenatal Screening Program provides pregnant women with a risk assessment for open neural tube defects (NTD), Down syndrome (trisomy 21), trisomy 18 and SLOS (Smith-Lemli-Opitz Syndrome) through one or two blood tests. The screening test indicates risk, but does not diagnose fetal birth defects. http://www.cdph.ca.gov/programs/PNS/Pages/default.aspx
For women with screening results indicating a high risk for a birth defect, the Program provides free follow-up diagnostic services at State-approved Prenatal Diagnosis Centers (PDCs) (PDF). Services offered at these Centers include genetic counseling, ultrasound, and amniocentesis. Participation in the screening testing and follow-up services is voluntary. The cost of the testing through the Prenatal Screening Program is $207.
Hope this information helped you to know more about prenatal DNA screening
Sources: I have used infornation on Stanford Children’s Health http://www.stanfordchildrens.org/ including images for this post
California Prenatal Screening Program http://www.stanfordchildrens.org/