Pros And Cons Of Prenatal Genetic Screening
Not all genetic testing has to be done during pregnancy. If two partners both belong to an ethnic group with a higher risk of certain genetic disorders, then the couple may undergo a test to see if they carry certain genes. This is called a carrier screening. Many genetic conditions such as Tay-Sachs, sickle cell disease, and cystic fibrosis require that both parents be carriers of the gene or genes.
This information can affect family planning choices, including whether to have children or to undergo IVF with preimplantation genetic screening.
Couples who discover that their baby has a genetic defect are generally referred to a genetic counselor to help them understand the condition and their options.
Genetic screening in pregnancy can determine the risk for birth defects and genetic conditions, but an actual diagnostic test can tell for sure. Couples who discover that their baby has a genetic defect are generally referred to a genetic counselor to help them understand the condition and their options.
Second Trimester Maternal Serum Screening
Second trimester screening, sometimes called a maternal serum screen or triple test, is done between 14 and 18 weeks into the pregnancy. It is usually offered to women who missed the combined first trimester screening test, or if it was not available where they were living.
It involves a blood test to look for hormones that could indicate the baby has Down syndrome or a neural tube defect. There will usually be a cost, but you can claim some of it back from Medicare.
If your baby is at increased chance, you will be offered a diagnostic test, which is optional, to confirm whether or not the baby has Down syndrome.
In addition to the MSS test, most pregnant women have a morphology scan at 18 to 22 weeks into the pregnancy to check on the babys growth and to see how the pregnancy is progressing. This can sometimes show signs of Down syndrome.
When Is The Right Time To Undergo Genetic Testing
Women have several options for genetic testing. You dont necessarily have to be pregnant to decide to have genetic screening. If you and your partner share a similar family history of conditions such as Down syndrome, Tay-Sachs, or cystic fibrosis, for example, then you may both wish to undergo carrier screening before deciding whether to become biological parents.
As we said earlier, most women undergo first-trimester screening. This is optional, but your obstetrician may recommend it. Its generally done after week 10 of pregnancy and strongly recommended if your pregnancy is considered high-risk.
If you didnt undergo first-trimester screening, you may opt for a maternal serum quad screening during your second trimester. This involves a blood draw and an analysis of certain protein markers in your blood that indicate if the fetus has trisomy 13 , trisomy 18 , or trisomy 21 . Neural tube defects, such as spina bifida are also part of the test. The quad screen may be completed any time between weeks 16 and 23 of pregnancy with the optimal time frame at weeks 1618 of gestation.
If you and your partner share a similar family history of conditions such as Down syndrome, Tay-Sachs, or cystic fibrosis, for example, then you may both wish to undergo carrier screening before deciding whether to become biological parents.
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What Does The Result Of Genetic Testing Convey
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If the Test Is Positive – That means that the baby is at higher risk of having the disorder when compared with the normal population. It does not mean that the baby definitely has the disorder.
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If the Tests Are Negative – That means that the baby is at a lower risk of having the disorder when compared to the normal population. It does not rule out the possibility that the baby has the disorder.
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Diagnostic Tests Results – Diagnostic testing provides a more definite result and is an option for all pregnant women.
The doctors and the genetic counselor will discuss what the screening test results mean and help in deciding the next steps.
Each woman and each pregnancy is different, and if family history or doctors detect certain illnesses, genetic abnormalities can occur. Choosing to have carrier screening and diagnostic testing is a personal choice. If a parent is considering prenatal genetic screening, it is good to have counseling with a genetic counselor who will help in guiding through the testing process and discussing the results.
What Are Some Of The Most Common Genetic Diseases
Cystic Fibrosis
Cystic fibrosis is a life-threatening condition that causes lung damage and digestive problems. About 30,000 people in the U.S. have the disease, which mostly affects Caucasians of Northern European descent. Organizations like the National Institutes of Health, the American College of Obstetricians and Gynecologists, and the American College of Medical Genetics have recommended nationwide genetic testing for CF for all adults since 2002. According to a recent study in the New England Journal of Medicine, the number of babies born with cystic fibrosis in Massachusetts dropped by about 50 percent in the four years after this recommendation was made and testing came into wider use compared to the four years before.
Sickle Cell Disease
This genetic condition is most common in people of African and Mediterranean backgrounds, causes a blood disorder that leads to anemia, a weakened immune system, and other health complications.
Thalassemia
Thalassemia is another blood disorder common to people of African and Mediterranean descent. It typically causes anemia and bone growth and liver problems in severe cases, some babies born with the condition may not survive.
Tay-Sachs Disease
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Who Should Undergo Genetic Testing
All pregnant women, regardless of risk level or age, are recommended for first-trimester screening. Besides this, genetic testing is usually offered to couples with a family history of certain conditions, or a higher risk is identified for a baby with a genetic health condition or birth defect. Whether to undergo genetic testing is a personal decision of the couple.
What Are Kick Counts And How Do You Do Them
Kick counts is a way for you to track how often your baby moves. By about 5 months of pregnancy, you should start to feel your baby move in your belly. Your baby can turn from side to side and sometimes head over heels. Tell your provider if:
- Youre at about 20 weeks of pregnancy and havent felt your baby move.
- Youre worried that your baby isnt moving.
- You notice a change in how often your baby moves, especially if movement decreases.
Your provider may ask you to do kick counts to see when and how often your baby moves. Here are 2 ways to do kick counts:
You can do kick counts into your third trimester. If your provider is concerned about your babys movements, they may do other tests to check on your babys health.
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What Are Screening Tests
Screening tests are used to find people at higher chance of a health problem.
This means they can get earlier, potentially more effective, treatment or make informed decisions about their health.
Screening tests are not perfect. Some people will be told that they or their baby have a higher chance of having a health condition when in fact they do not have the condition.
Also, a few people will be told that they or their baby have a lower chance of having a health condition when in fact they do have the condition.
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When Are Screenings Done
Genetic screening tests can be done at two times during your pregnancy a test between weeks 11 and 14 is called a first trimester screening, and a test between weeks 15 and 22 is called a quad screening. For genetic screening tests to provide accurate results, its important to know when your baby was conceived
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Path To Improved Health
Most prenatal screenings occur when you are 15-20 weeks pregnant. The primary screenings are optional. But all pregnant people are offered the tests. Some choose not to do the screenings. There are three primary screenings that begin with a blood test: triple screen, quad screen, and penta screen. The blood tests look for different proteins in the blood.
- Triple screen: this test measures three substances in a pregnant persons blood. These substances include alpha-fetoprotein , human chorionic gonadotropin , and unconjugated estriol.
- Quad screen: A quad screen measures four things in a pregnant persons blood. This includes AFP, hCG, unconjugated estriol and inhibin A.
- Penta screen: A penta screen measures all of the above, plus the substance hyperglycosylated human chorionic gonadotropin.
- Cell-free DNA: this newer blood test can be performed after 10 weeks of pregnancy. This blood test may be more sensitive than the others. It collects DNA from the baby that is present in the mothers bloodstream. It uses these DNA fragments to predict the babys risk for birth defects.
None of these blood screenings pose a risk to mom or baby. If you choose to do a screening, you and your doctor can decide which one is best for you.
What Prenatal Tests Do You Get All Through Pregnancy
These prenatal tests may be done several times during pregnancy:
- Blood pressure check. Your provider checks your blood pressure to make sure you dont have preeclampsia. Preeclampsia is high blood pressure that can happen after the 20th week of pregnancy. Preeclampsia can cause serious problems during pregnancy.
- Urine test. Your provider checks your urine for infections, like a bladder or kidney infection, and other conditions, like preeclampsia. Having protein in your urine may be a sign of preeclampsia.
- Blood tests. Your provider checks your blood for certain infections, such as syphilis, hepatitis B and HIV. Your blood test is also used to find out your blood type and Rh factor and to check for anemia. Anemia is when you don’t have enough healthy red blood cells to carry oxygen to the rest of your body. Rh factor is a protein that most people have on their red blood cells. If you dont have it and your baby does, it can cause Rh disease in your baby. Treatment during pregnancy can prevent Rh disease.
Your provider will probably check your weight at each prenatal care checkup to make sure youre gaining the right amount.
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What Is Noninvasive Prenatal Testing And What Disorders Can It Screen For
Noninvasive prenatal testing , sometimes called noninvasive prenatal screening , is a method of determining the risk that the fetus will be born with certain genetic abnormalities. This testing analyzes small fragments of DNA that are circulating in a pregnant womans blood. Unlike most DNA, which is found inside a cells nucleus, these fragments are free-floating and not within cells, and so are called cell-free DNA . These small fragments usually contain fewer than 200 DNA building blocks and arise when cells die off and get broken down and their contents, including DNA, are released into the bloodstream.
During pregnancy, the mothers bloodstream contains a mix of cfDNA that comes from her cells and cells from the placenta. The placenta is tissue in the uterus that links the fetus and the mothers blood supply. These cells are shed into the mothers bloodstream throughout pregnancy. The DNA in placental cells is usually identical to the DNA of the fetus. Analyzing cfDNA from the placenta provides an opportunity for early detection of certain genetic abnormalities without harming the fetus.
NIPT is most often used to look for chromosomal disorders that are caused by the presence of an extra or missing copy of a chromosome. NIPT primarily looks for Down syndrome , trisomy 18 , trisomy 13 , and extra or missing copies of the X chromosome and Y chromosome . The accuracy of the test varies by disorder.
How Can I Arrange Carrier Status Screening
Carrier screening is usually requested by a doctor, obstetrician, fertility specialist, midwife or genetic counsellor. They will fill out a test request form that you take to your local pathology collection centre for the blood test. The genetic testing will be done in a specialist laboratory.
Make sure you tell the person who is ordering the test if you have a family history of a genetic condition, so they can order the most appropriate test.
In Australia, carrier status screening can cost several hundred dollars per person. You cannot claim any of the money back on Medicare. Some private health funds will pay part of the cost if you have a family history of some genetic diseases.
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What Other Tests Are Done In The First Trimester
After the first visit, you can expect to get your urine tested and your weight and blood pressure checked at every visit until you deliver. These tests can find problems such as gestational diabetes and preeclampsia .
During your first trimester, youll be offered more tests depending on your age, health, family medical history, and other things. These can include:
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Total Confidence In Every Result
Those shortfalls are rarely referenced when companies explain the tests to doctors and patients.
A Labcorp MaterniT21 lab report tells patients the test detected a problem, even though most studies show positives on that screening are usually wrong. Myriad Genetics advertised total confidence in every result on its prenatal testing website but said nothing about how often false positives can occur.
After The Times inquired about these tests, Myriad took down that language.
The Times reviewed 17 patient and doctor brochures from eight of the testing companies, including Natera, Labcorp, Quest and smaller competitors. Ten of the brochures never mention that a false positive can happen. Only one mentioned how often each test gets positive results wrong.
Examples of positive
A footnote defines high probability
as 1% or greater.
Genetic counselors who have dealt with false positives say some doctors may not understand how poorly the tests work. And even when caregivers do correctly interpret the information, patients may still be inclined to believe the confident-sounding results sheets.
When Cloey Canida, 25, got a positive result from Roches Harmony test in September, the result sheet seemed clear:It said her daughter had a greater than 99/100 probability of being born with Patau syndrome, a condition that babies often do not survive beyond a week.
Kitty Bennett contributed research.
About the analysis
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What Are The Diagnostic Tests Carried Out To Check The Genetic Problems
There are two common diagnostic tests that are chorionic villus sampling and amniocentesis. Both tests are invasive and involve taking cells from the fetus and analyzing the cells under a microscope. This helps in determining whether the chromosomes are damaged or the fetus has few or many chromosomes present which could result in a genetic problem.
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Chorionic Villus Sampling – This test is done during the first trimester of pregnancy normally at 10 to 12 weeks. CVS tests involve collecting a small part of the placenta in the uterus. The doctor collects the tissue either with a needle through the mother’s stomach or using a thin tube into the cervix. There can be cramps, infection, or bleeding for some women. This test cannot identify neural tube defects.
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Amniocentesis – In this test the doctor puts a thin, long needle through the mother’s stomach into the sac that surrounds the fetus to take out a small amount of fluid. The proteins and cells in the amniotic fluid are then checked in a laboratory. The test is performed between 15 weeks and 20 weeks of pregnancy. Amniocentesis can cause cramping, bleeding, or infection.
What Should Be Done After A Positive Genetic Screening Test
A positive screening test should be followed by a diagnostic test. This means testing the fetus directly. This can be done before birth through an invasive procedure, most often amniocentesis. Some families wait to test the baby after they are born. Testing the fetus or baby directly will tell if there is a chromosome disorder.
A family can feel much more confident that their fetus does not have a chromosome disorder if a genetic screening test is negative.
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Why Is It Important To Do Genetic Testing During Pregnancy
Many genetic abnormalities can be evaluated or diagnosed before your baby is born . This depends on the family history and if a known disease-causing mutation has been already identified in the family.
Your obstetrician may recommend that you and your family meet with a geneticist and genetic counselor to arrange for genetic screening tests and/or genetic diagnostic tests during the pregnancy if:
- you or your partner has a family history of genetic disorders
- you have had a prior fetus or baby with a genetic abnormality
- an abnormality may be suspected on a fetal ultrasound.
Genetic counseling is always recommended prior to any prenatal diagnostic testing for genetic disorders. This is also available for couples who have general questions or concerns.
What Happens During A Genetic Test
Most often, pregnant women undergo genetic screening tests, which can help tell them if their baby is at high risk for having a genetic disorder.
A screening typically consists of a blood test and an ultrasound performed by one of our maternal-fetal medicine specialists, to improve the accuracy of the screening. Genetic screenings cannot identify all birth defects, and a screening does not provide a definitive diagnosis of a genetic disorder. If a screening result is abnormal, youll be referred to our maternal-fetal medicine team for further testing.
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