Understanding prenatal testing

Pregnancy is a time of great anticipation, and you’ll probably find yourself asking questions like these: Will it be a girl or a boy? Will the baby have your smile or his eyes? Will it have curly or straight hair?

But more than those relatively ‘shallow’ questions, more important ones about your baby’s health surface and can potentially overwhelm you: Will he or she be born with any abnormalities or birth defects? Will you experience any complications during birth? Will my baby be 100% healthy?

Now, while most babies are born healthy, concerns such as the ones mentioned are natural. Fortunately, you can take comfort in the fact that there are a number of tests available that can help identify potential health problems for you and your unborn child, some of which are treatable.

Thus, it is important to educate yourself and anticipate what you need to do, should any problems be detected. Remember, early detection means more time for treatment and planning of various courses of action.

Pregnancy screening: What is a Prenatal Test

Some prenatal tests are routine in pregnancies and are mostly screening tests. These include blood tests and ultrasounds that can only identify if your baby is likely to have certain conditions. However, it cannot be diagnose with certainty.

Diagnostic tests, on the other hand, will either be suggested to you or you may opt to take them. They usually test for chromosomal disorders. Which refer to an abnormality in the structure or number of chromosomes.

The chance of a child being born with these disorders increases if the expectant mother is older. For example, the American College of Obstetricians and Gynecologists found that 1 in 1,667 babies born to women in their early 20s has Down syndrome. However, this number increases to 1 in 378 in women in their mid-30s and 1 in 106 for 40-year-old women.

Thus, doctors would usually recommend older women or women with a family history of genetic disorders take these tests. However, an expectant younger mom or one without any history can opt to take them as a precautionary measure as well.

If you’re pregnant, here are some diagnostic prenatal tests to consider:

Genetic Testing during pregnancy

While still in the womb, several tests can detect medical abnormalities in newborns. Others examine their DNA for signs of genetic diseases. Genetic carrier screenings can be done even before conception to predict the risk that their child would be born with a genetic disease.

The bulk of the tests are optional, but they can help you make health decisions and prepare for the arrival of your kid.

A carrier is someone who carries the gene for an illness but does not suffer from it. Genetic carrier screening assesses whether you and your partner both contain certain genes and, if so, how likely it is that they will be passed down to your children.

The tests can be used before or throughout pregnancy, but they are most helpful before.

A doctor will take a sample of your blood or saliva for testing. The lab can look for genes for a range of diseases. But the most prevalent ones are:

• Tay-Sachs disease
• Fragile X syndrome
• Spinal muscular atrophy
• Cystic fibrosis
• Sickle cell disease

Ask your doctor if you fall into this category because some ethnic groups are more prone to be carriers of certain diseases. Carrier testing may assist non-Hispanic whites (cystic fibrosis), Eastern European Jewish people (Tay-Sachs disease, cystic fibrosis, and other diseases), and people from Africa, the Mediterranean, and Southeast Asia (sickle cell disease).

• Genetic syndromes

Diseases that emerge as a result of genetic alterations are known as genetic syndromes. Genes are DNA segments that contain protein-making instructions.

They have a wide range of functions, including defining cell shape, and structural functions, and controlling practically all metabolic processes.

Proteins are absolutely necessary for our bodies to function properly. A mutation in the genes, on the other hand, can lead them to lose their “code,” causing them to malfunction as a result of the altered information they acquire as they form. Genetic abnormalities may arise as a result.

How are genetic syndromes passed?

Genes are squeezed within chromosomes. The human genome’s 46 chromosomes are divided into 23 pairs of homologous chromosomes. The sex chromosomes, which determine an individual’s gender, are the last pair, and the rest is autosomal.

One or both parents can pass down a genetic mutation. Mutations, on the other hand, might occur by chance throughout our lifetimes.

During conception, each parent contributes a set of chromosomes, a unit from each spouse. If the groups of chromosomes change, it can be passed on to the children.

Types of Genetic Syndromes

• Chromosomal abnormalities occur when one of the chromosomes in a homologous pair is absent or when there are too many. This is known as aneuploidy, and it becomes more likely as a mother gets older. People with Down’s Syndrome have a trisomy (three chromosomes) of chromosome 21, for example.
• Autosomal genetic disorders. The autosomal chromosomes are impacted by one or more genes. It’s a recessive disorder if both parents have the mutation. When only one parent has the faulty gene, we’re talking about dominant disorders. A dominant genetic disease such as Huntington’s Disease is an example.
• Sexually transmitted illnesses. Chromosome mutations in the sex chromosomes are what these are (pair 23). X-linked hemophilia is one of the most common sex-related genetic diseases in humans.
• Multifactorial disorders. These are genetic and environmental factors that influence the expression of one or more genes. Surgical treatment for neural tube issues, for example, is available.

Tests for Genetic Syndromes

Prenatal genetic testing can detect genetic disorders in our unborn child while she is still in the womb. Your gynecologist may request extra tests based on risk factors such as age or family history. These screening and diagnostic tests are, of course, optional.

Aside from the prenatal test in the first trimester, the most common tests include amniocentesis and blood testing for genetic disorders.

• Amniocentesis is a process in which amniotic fluid and cells are extracted from the sac by puncturing the abdominal wall. It can almost 100% reliably confirm the presence of a mutation. However, it is an invasive test with a 1% possibility of miscarriage.
• On the other hand, a test for genetic abnormalities is a non-invasive process that just requires a little sample of the mother’s blood. It enables the detection of genetic abnormalities connected to trisomies 21, 18, and 13.

Pregnancy Screening by Trimester

Here are some tests you should consider taking depending on the trimester you are in:

1. First Trimester Prenatal Test

When you become pregnant, your doctor may recommend that you have your baby’s DNA tested to rule out any medical issues. Common tests in the early stages of pregnancy include:

• Sequential Screening or prenatal testing for down syndrome

Using a combination of ultrasound and blood testing, this test screens for Down syndrome, trisomy 18, and spine and brain problems. It usually happens between weeks 10 and 13. If the test findings are negative, you can have additional testing during your second trimester.

• Integrated Screening 

Another prenatal testing for Down syndrome, trisomy 18, and spine and brain problems. You get it about 12 weeks, and the remainder of it happens throughout your second trimester.

It’s more precise than a sequential screen, but it takes a little longer to get the results – until the second section of the test is finished.

• Cell-free fetal DNA Testing

Some of your baby’s DNA is present in your blood. Your doctor will collect a sample from you after 10 weeks. Which will be evaluated in a lab for symptoms of:

• • Down syndrome
  • Trisomy 18
  • Trisomy 13
  • Issues with sex chromosomes

If any of your screening tests suggest a risk of birth abnormality, your doctor may offer a diagnostic test to confirm the findings. Because the cell-free DNA test does not examine for problems with the brain or spine, if you get it, you can have a blood test done in your second trimester to check for those concerns.

It may be useful to test the father as well. Some conditions can only be handed along if both parents have the gene. Your doctor may be able to rule out Tay-Sachs, cystic fibrosis, and sickle cell anemia if the father tests negative — even if you test positive.

READ MORE: 

What are the risks? Pregnancy in your 20s, 30s, 40s

What are the 3 trimesters of pregnancy? A guide for pregnant women

Guide to your 5 weeks pregnancy: Symptoms and the development of your baby

2. Second Trimester Prenatal Test

• AFP (alphafetoprotein) test

This examination searches for issues in the neural tube. It is usually done if the patient has already had a cell-free DNA test, which does not screen for these types of abnormalities.

• Maternal serum quad screen

This blood test looks for proteins in your blood that could suggest if your baby has Down syndrome, trisomy 18, or spine or brain problems. Your doctor can administer the test between 15 and 21 weeks.

• Integrated screening

If you have the first component of this test in your first trimester, you’ll have another blood test between 16 and 18 weeks.

• Ultrasound

A technician uses a gadget to create photographs of your baby using sound waves about week 20. These images are used by your doctor to check for birth defects such as cleft palate, heart difficulties, and kidney problems.

Other Types of Prenatal testing

1. Amniocentesis

Usually conducted to detect chromosomal abnormalities such as Down syndrome, inherited metabolic disorders, and some fetal infections.

The test should be taken if you are above 35 years of age, have had a child with a birth defect, have a family history of genetic disorders, or had an abnormal screening test. It is often performed between the 15th and 20th weeks of pregnancy.

The doctor will remove some amniotic fluid through the abdominal wall in the uterus during an ultrasound scan with a very thin needle. These cells are grown in a special culture and analyzed.

During the procedure, you may experience slight pressure or pain, but usually nothing more. Test results are ready within 1 to 2 weeks.

Injury to the baby is rare. The risk of miscarriage is 1 in every 200 procedures. There is also a low risk of uterine infection and leakage of amniotic fluid.

2. Chorionic Villus Sampling(CVS)

Usually conducted to detect chromosomal abnormalities such as Down syndrome and inherited disorders. The advantage of this test over amniocentesis is that it can be performed earlier, allowing parents to make decisions and receive counseling.

The test should be taken if you are above 35 years of age, have had a child with a birth defect, have a family history of genetic disorders, or had an abnormal screening test. Often performed between the 10th and 12th week of pregnancy.

A needle is used to extract tiny placental tissue from your placenta during an ultrasound scan. The tissue is tested for birth defects because the baby originates from the placenta and the specimen would thus have the same chromosomes present in the unborn baby.

Mild pain is felt during the procedure and local anesthesia is used. Test results are ready within 1 to 2 weeks. About 1% of CVS performed to result in miscarriage. There are also risks of infection and birth defects developing if the test is done too early in pregnancy.

3. Fetal Blood Sampling (FBS)

Usually conducted to detect chromosomal abnormalities such as Down syndrome, inherited disorders, infections that can affect the fetus, and anemia or low platelet levels in the fetus. The major advantage of this test is that it can be carried out quickly, which is helpful when the fetus is in distress.

The test should be taken after an abnormality is noted on a screening test such as an ultrasound. When other test results are not conclusive, or when you have been exposed to an infectious disease that could affect your fetus.

Often performed between the 18th and 23rd week of pregnancy. A fine needle is guided from the abdomen and into the uterus to extract blood from the fetus during an ultrasound scan.

Mild pain may be felt during the procedure and local anesthesia is used. Test results are ready within 3 to 5 days. About 1% to 1.5% of FBS performed result in miscarriage.

4. Double marker test in pregnancy

The maternal serum screening, also known as the double marker test, is part of the first trimester screening, which is a more extensive examination. It’s a predictive test, which means the results forecast the possibility of chromosomal abnormalities.

This test examines the blood for levels of free beta-human chorionic gonadotrophin (beta-hCG) and pregnancy-associated plasma protein A. (PAPP-A).

Female fetuses have 22 pairs of XX chromosomes, while male fetuses have 22 pairs of XY chromosomes in a typical pregnancy.

A trisomy is a chromosomal abnormality characterized by the presence of extra chromosomes, such as:

• Down syndrome is a hereditary condition. This common trisomy is also known as trisomy 21 because it has an extra copy of chromosome 21.
• There are two forms of trisomy: trisomy 18 and trisomy 13. Several frequent chromosomal abnormalities are caused by an extra copy of chromosome 18 (Edward’s syndrome) or chromosome 13 (Patau’s syndrome).

A double marker test and an NT scan are included in the first trimester screening, which is optional. It is recommended if you aged 35 and above or have a high risk of chromosomal abnormalities, such as if you have a family history of particular diseases.

It’s important to remember that the result only tells you whether you’re at risk for trisomies. It is unable to determine whether or not your baby is abnormal.

The time window in which the double marker test can be performed is limited. Your doctor will ask you to make an appointment near the end of the first trimester or very early in the second trimester. Blood will be drawn between weeks 11 and 14, to be exact.

The Double Marker Test is a simple blood test that doesn’t require any preparation. On the other hand, the doctor must be scared of the medications that will be administered before to the test.

The cost of a double marker test depends on your insurance coverage and where you live. While the test is optional, it may be covered by your health insurance policy.

Standard vs Abnormal Results

A “normal” test (low-risk or “screen-negative”) implies that your baby is unlikely to have chromosomal abnormalities.

If your result falls within the normal range, you will only be referred for further testing if there is another indicator (such as family history, age, or other characteristics) or if you want to learn more for another reason.

However, a low-risk result does not guarantee that your child will have no difficulties. It’s also worth mentioning that the first-trimester screening only looks for markers for Down syndrome, trisomy 13, and trisomy 18, and nothing else.

If your screening for anomalies results in a moderate- or high-risk result (“screen-positive”), you should talk to a genetic counselor to learn more.

Noninvasive prenatal testing (NIPT), amniocentesis, and chorionic villous sample are more conclusive and often invasive procedures that can be utilized to validate your results. While some of these tests may put your pregnancy in danger, they provide you with a definitive answer.

Risks

There are no drawbacks to the double marker test. It’s a simple, non-invasive blood test. Naturally, follow your doctor’s advice and contact him or her if you have any questions or concerns.

What is the difference from NT?

For the most reliable results, the double marker test (blood test) and NT scan (ultrasound) are utilized together in the first-trimester screening. The findings of both tests are used to assess if the risk of abnormalities is low, moderate, or high.

When the NT scan is performed without the double marker test, it is less effective in detecting possible abnormalities.

During an NT scan, your healthcare provider can use sound waves to obtain a real-time image of your baby. It occurs concurrently with your double marker test.

Other prenatal tests during pregnancy

5. Nuchal translucency scan

Nuchal translucency is the appearance of fluid beneath the skin behind the fetal neck in the first trimester of pregnancy. The term translucency is used regardless of whether it is septated or not, and whether it is confined to the neck or surrounds the entire fetus. In fetuses with chromosomal abnormalities, cardiac difficulties, and a variety of genetic illnesses, the NT thickness is increased.

NT screening can detect:

• around 80% of fetuses with trisomy 21 and other severe aneuploides
• with a false positive rate of 5%.

When NT is combined with maternal serum free-hCG and PAPP-A, detection is increased to 90%. There is currently evidence that evaluating the nasal bone, ductus venosus flow, and tricuspid flow can improve detection rates to around 95% and reduce false-positive rates to 3%.

The sonographer confirms your baby’s gestational age by measuring them from crown to rump to see if they’re the proper size for their age. The sonographer next places a sensor on your abdomen called a transducer so that your baby’s nuchal translucency appears on the monitor and uses calipers to assess its thickness of it.

How are results calculated

• Your age
• your baby’s gestational age
• blood test results

While anyone can have a child with a chromosomal issue, the risk of having a child with a chromosomal issue increases with age. Your chances of having a baby with Down syndrome, for example, rise from roughly 1 in 1,200 at 25 to 1 in 100 at 40.

Your results will be presented to you as a ratio indicating the likelihood of your baby having a chromosomal issue.

For example, a risk of 1 in 100 means that one baby will be born with Down syndrome for every 100 moms who have this result, whereas the other 99 will not.

A risk of 1 in 1,200 means that for every 1,200 moms who have this test, one baby will have it, while the other 1,199 will not. The greater the second number, the lower the risk.

Whether the ratio is below or above a given cutoff, you may be told that your NT results are “normal” or “abnormal” for a particular condition.

Some tests, for example, have a 1 in 250 cutoffs. As a result, a 1 in 1,200 results is considered normal because the chance of a problem is less than 1 in 250. A ratio of 1 in 100 would be considered abnormal because the danger is greater than 1 in 250.

How accurate is the test?

The NT scan can detect 70 to 80 percent of Down syndrome babies. The detection rate of the NT scan paired with a first-trimester blood test is 79 to 90%.

What happens if my NT scan indicates a problem?

With the help of your doctor, you can determine whether the results indicate a high enough risk that you require CVS or amniocentesis for a definitive diagnosis.

6. Thalassemia screening test

Before getting pregnant, partners are screened for Thalassemia with a test called hemoglobin electrophoresis or another test called HPLC (HPLC test).

A Complete Blood Count (CBC) blood test can be done to determine the number of red blood cells and any abnormalities in the hemoglobin content.

How is it inherited

Your baby has Thalassemia if both you and your partner have the Thalassemia trait/are silent carriers, according to your test results.

• There’s a 25% possibility you won’t get a Thalassemia major or become a carrier.
• The probability of becoming a carrier is 50%. (Thalassemia phenotype)
• You stand a 25% chance of developing the disease (Thalassemia major)

What are symptoms

• Urine is a dark color.
• Yellow or pale-colored skin
• Growth is slow.
• Facial asymmetry
• I’m completely spent (more than usual during pregnancy)
• Breathing difficulties

Because thalassemia causes a drop in hemoglobin levels, the symptoms are similar to those of anemia. Pregnant women often have low hemoglobin levels. As a result, it’s simple to confuse it with anemia caused by pregnancy.

Who should test and when to do it

Because thalassemia can be passed down from generation to generation, you and your partner should get tested if you are getting married or starting a family.

A blood transfusion may be advised as the best treatment option if you or your children have thalassemia. Additional therapies include iron chelation therapy and a bone marrow transplant.

If you have thalassemia or are at risk of developing it, your doctor may recommend folic acid pills as one of the first treatments. Folic acid is necessary for a healthy pregnancy and should be taken by all pregnant women.

7. Antenatal screening

The antenatal profile test is an important component of prenatal care that can help you and your baby stay healthy throughout your pregnancy.

Blood tests, urine tests, and ultrasound scans are among the tests used to examine various aspects of your and your baby’s health. Some tests are advised for all women, while others are only for those who are at a higher risk of contracting a specific condition.

Screening tests are included in several prenatal diagnostics. In line with this, it implies they’re made to assess if you or your child are at danger of developing a disease. If a screening test indicates a high-risk result, you may choose to get your child tested for the disorder.

At your initial antenatal visit, your doctor or midwife will discuss which antenatal tests are recommended for you and when you should have them.

Several types of prenatal tests are available at various periods throughout pregnancy, including blood tests, urine tests, ultrasound scans, and special testing.

Antenatal tests are an important tool for monitoring your and your baby’s health during pregnancy. Antenatal testing can help with the following:

• Medical disorders that are detected early can be treated early.
• To determine what to do next, find out whether your child has any hereditary concerns.
• Check to see if your child is developing normally.

Overall, there are a number of tests available that can help identify potential health problems for you and your unborn child. It is important to educate yourself and anticipate what you need to do, should any problems be detected. Remember, early detection means more time for treatment and planning of various courses of action.

Did you have any prenatal tests done when you were pregnant? Let us know by leaving a comment below!

Updates by Margaux Dolores

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