Posts Tagged ‘maternal blood screening’

Screening vs. diagnostic testing—what’s the difference?

Friday, June 26th, 2015

DoctorPregnant_zps3ac96800If you are pregnant, you know that every visit to your prenatal care provider involves a number of tests. At each prenatal checkup, your provider checks your weight, blood and urine. But in addition to these routine tests, you will also be offered prenatal tests that can assess your risk to have a baby with certain birth defects.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women, regardless of age, be offered prenatal testing for Down syndrome and some other birth defects. There are two different types of tests that you can have: a screening test or a diagnostic test. It’s important to understand the difference between a screening test and a diagnostic test. Screening tests help evaluate the risk for certain birth defects, but they cannot diagnose a birth defect. Screening tests pose no risk to mother or baby. Diagnostic tests are highly accurate at diagnosing or ruling out specific birth defects. However, these tests may pose a very small risk of miscarriage.

Screening tests offered during pregnancy include:

  • Cell-free fetal DNA testing (also called noninvasive prenatal screening or testing): Some of your baby’s cells can be found in your blood. This test uses a sample of your blood to look at your baby’s DNA to check for certain genetic conditions. You can have this test after 10 weeks of pregnancy. This test is not recommended for women who aren’t likely to have a baby with a birth defect or who are pregnant with multiples.
  • First-trimester screening: Using a blood sample and ultrasound measurements, first-trimester screening can tell you if your baby is at risk for some birth defects, like Down syndrome. It is usually done between 11 to 13 weeks of pregnancy.
  • Maternal blood screening: This test measures four substances in your blood to determine the chance that a woman has a baby with certain birth defects like Down syndrome and neural tube defects. The test is done between 15 to 20 weeks of pregnancy.

Diagnostic tests are done by obtaining samples of your baby’s actual cells and therefore are more invasive. Diagnostic testing can detect most birth defects caused by a change in the number or shape of chromosomes. And testing for many inherited disorders can be done as well. However, not all birth defects can be detected.

Some women may choose to have diagnostic testing done instead of screening tests based on their age or family history. Other women may choose to start with a screening test and then, depending on the results, decide whether to have a diagnostic test. Prenatal diagnostic tests do carry a small risk of miscarriage (about 1 in 300-500).

  • Chorionic villus sampling (also called CVS): During this procedure, the doctor removes a small sample of tissue from the placenta. This can either be done transvaginally or transabdominally. You can get CVS at 10 to 12 weeks of pregnancy.
  • Amniocentesis (also called amnio): Your health care provider will use a needle to remove a small amount of amniotic fluid. Amnio is done between 15 to20 weeks of pregnancy.

Remember, all of these tests are optional. Make sure that you discuss your questions and concerns with your health care provider.

Questions? Send them to AskUs@marchofdimes.org.

 

Chromosomal abnormalities

Tuesday, August 20th, 2013

chromosomes1About 1 in 150 babies in the US is born with a chromosomal condition. Babies with chromosomal conditions have a problem in one or more of their chromosomes. Chromosomes are the structures that hold genes. Genes are part of your body’s cells that store instructions for the way your body grows and works. Genes are passed from parents to children.

Each person has 23 pairs of chromosomes, 46 in all. For each pair, you get one chromosome from your mother and one chromosome from your father.

Chromosomal conditions are caused by two kinds of changes in chromosomes:
1. Changes in the number of chromosomes—This means there are too many or too few chromosomes.
2. Changes in the structure of chromosomes—This means that part of a chromosome may be missing, repeated or rearranged.

Chromosomal conditions usually result from an error that occurs when an egg or sperm cell develops. It is not known why these errors occur and as far as we know, nothing that a parent does or doesn’t do before or during pregnancy can cause a chromosomal abnormality in their child. In some cases these kinds of changes can be inherited or passed from parent to child.

In most cases, an embryo with the wrong number of chromosomes does not survive. In such cases, the pregnant woman has a miscarriage. This often happens very early in pregnancy, before a woman may realize she’s pregnant. More than 50 percent of first-trimester miscarriages are caused by chromosomal abnormalities in the embryo.

The American College of Obstetricians and Gynecologists recommends that all pregnant women be offered a screening test for Down syndrome and certain other chromosomal abnormalities. Screening may consist of a maternal blood test done in the first trimester (at 11 to 13 weeks of pregnancy) along with a special ultrasound of the back of the baby’s neck. It also can be a maternal blood test done in the second trimester (at 15 to 20 weeks). A screening test helps identify pregnancies that are at higher-than-average risk of these conditions.

However, a screening test cannot diagnose Down syndrome or other chromosomal abnormalities. If a screening test shows that your baby may have a problem, your provider gives you a diagnostic test that can tell you if your baby actually does or does not have a chromosomal condition.

Diagnostic tests include amniocentesis or chorionic villus sampling. Your provider also can check your baby’s blood for chromosomal conditions after he’s born.

Each child born with a chromosomal condition is different. Some children with chromosomal conditions have intellectual disabilities or birth defects, or both. But some children with these conditions don’t have any serious problems. The problems depend on which chromosomes are affected and how they are affected.

If you or someone in your family has a chromosomal condition, or if you have a baby with a chromosomal condition, talk to a genetic counselor. A genetic counselor can help you understand the causes of chromosomal conditions, what kind of testing is available, and your chances of having a baby with these conditions.

New prenatal blood test

Thursday, December 13th, 2012

New prenatal tests can give some parents piece of mind that the baby they’re expecting doesn’t have a disorder.  The tests are given sooner and with greater accuracy and less risk of miscarriage than current tests.

The new tests, which use fetal DNA suspended in the mother’s blood, can test for chromosomal disorders such as Down syndrome (trisomy 21) and trisomy 18, and Rh blood incompatibility. They also can determine the baby’s gender, which allows health care providers to screen for disorders such as hemophilia.

During pregnancy, fetal cells and cell-free fetal genetic material circulate in the mother’s bloodstream.  This DNA can be used to screen for certain genetic disorders without having to perform invasive procedures such as amniocentesis or CVS (chorionic villus sampling).

At present four widely used procedures assist health care providers in prenatal diagnosis. They are:
Amniocentesis: a procedure that collects some of the amniotic fluid that surrounds the fetus for analysis. This is a diagnostic test.
Chorionic villus sampling (CVS): a procedure that obtains tissue from around the placenta. This is a diagnostic test.
• Maternal blood tests: screening tests that use mother’s blood to help identify problems with the fetal brain, spinal cord, intestines or chromosomes. These tests include alpha-fetoprotein (AFP), hCG and other hormones. As with all forms of screening, abnormal results require follow-up testing to make a diagnosis.
Ultrasound: a scan using sound waves to visualize the fetus.

Cell-free DNA methods of screening are a new option. “Prenatal diagnosis gives parents important information about the health of their baby and the status of their pregnancy. More often than not, prenatal screening reassures parents that their baby is healthy and that these disorders are not present,” says Joe Leigh Simpson, MD, March of Dimes senior vice president for Research and Global Programs.  “For a high-risk infant, prenatal diagnosis gives parents and health care providers options that may include planning for a health problem or arranging for delivery in a medically appropriate setting. The first step toward treating these problems is diagnosing them, and cell-free DNA methods, without the need for invasive measures, are welcomed.”

Dr. Lee P. Shulman of Northwestern University says, “while this represents a profound improvement in our ability to identify women at increased risk for carrying fetuses with the most common chromosome abnormalities, still, this technology represents a limited screening protocol and should not serve as a substitute for diagnostic tests such as chorionic villus sampling and amniocentesis, which provide the most accurate and comprehensive assessment by the direct analysis of fetal tissue.”

The American College of Obstetricians and Gynecologists and the American College of Medical Genetics recommend that information on prenatal genetic screening and diagnosis should be made available to all pregnant women and those considering pregnancy.

With all the above options for testing available, it’s important to discuss what is best for you and your pregnancy with your health care provider.

Choroid plexus cysts

Friday, December 3rd, 2010

Sometimes technology can be a double-edged sword.  For instance, we all love seeing those first ultrasound pictures of our babies—it is so exciting and amazing!  But ultrasound can also show us things that may or may not have consequences.  Choroid plexus cysts are an example.

The choroid plexus is the area of the brain that produces the fluid that surrounds the brain and spinal cord. This is not an area of the brain that involves learning or thinking. Occasionally, one or more cysts can form in the choroid plexus. These cysts are made of blood vessels and tissue. They aren’t a problem by themselves and they do not cause developmental delays or learning problems.

Using ultrasound, a health care provider can see these cysts in about 1 in 120 pregnancies at 15 to 20 weeks gestation. Most disappear during pregnancy or within several months after birth and are no risk to the baby.

However, if choroid plexus cysts are present and maternal blood testing (such as the quad screen) and/or the ultrasound itself shows other signs of risk, together it may all indicate a possible genetic defect. In this case, testing with higher-level ultrasound and amniocentesis may be offered to confirm or rule out serious problems.

Hearing your baby has choroid plexus cysts can be scary but don’t panic.  Just remember that most of the time this is a benign finding and does not mean that there is a problem.

Do those blood tests confuse you?

Monday, August 9th, 2010

For those of you who are pregnant, sometime between 15-20 weeks of pregnancy, you will be offered maternal serum screening.  What is this?  And more importantly, what do the results mean?  I think maternal blood screening is one of the most misunderstood tests in pregnancy.  And for some women it can be a very nerve-wracking experience.

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women regardless of age be offered a screening test for Down syndrome and certain other birth defects.  This is a blood test that looks at the levels of either 3 or 4 (depending on the test) chemicals that are present in a pregnant woman’s blood.  The chemicals are AFP (alpha fetoprotein), hCG (human chorionic gonadotropin—the same chemical that a home pregnancy test measures), estriol, and recently most labs have added a fourth substance, inhibin A.  These chemicals are present in every pregnant woman’s blood.  Some of them are produced by the fetus while others are hormones produced by the placenta.

Maternal serum tests such as the triple screen or the quad screen as they are commonly called, look at the levels of these 3 or 4 chemicals in the mother’s blood and the woman’s age, weight, race, number of fetuses (e.g. twins) and whether she has diabetes that requires insulin treatment.  Then given all of those factors and the levels of the 3 or 4 chemicals the laboratory can determine the chance that a woman has a baby with Down syndrome, a neural tube defect (spina bifida), trisomy 18, or abdominal wall defects.

There are two different ways that the results may be reported.  A woman may receive her test result as a ratio. For example, her baby has a 1 in 500 chance for Down syndrome. Or, in some cases, a woman’s test results are reported as normal (screen negative) or abnormal (screen positive), depending on whether her results fall below or above a cut-off point (usually about 1 in 270).

The test is NOT a diagnosis of any of these conditions though.  This is where there is a lot of confusion.  By definition, screening tests do not diagnose a condition.  They only determine whether there is an increased risk for the condition.  The good news is that of all of the women who screen positive, only a small percentage will actually have a baby with one of these disorders.  Many times women have an abnormal result simply because their fetus is a few weeks older or younger than previously thought.

For women with abnormal results, the next step is usually an ultrasound. This test can check the gestational age of the fetus and show if a woman is carrying multiples. If either of these factors accounts for the abnormal test result, no further testing is needed. If ultrasound does not explain the abnormal test result, amniocentesis will be offered.  An amniocentesis is an invasive test where the doctor uses a needle to remove some of the amniotic fluid around the baby.  Although amnio does pose a very slight risk of miscarriage (1/4 of one percent or 1/500), it is extremely accurate and usually can give a pregnant woman a definitive answer.  Should a problem exist, arrangements can be made in advance for special care of the newborn at delivery.

Is genetic counseling for you?

Tuesday, January 26th, 2010

genetic-counselorAnyone who has unanswered questions about diseases or traits that run in the family should consider genetic counseling. People who may find it valuable include:
• Those who have, or are concerned that they might have, an inherited disorder or birth defect.

• Women who are pregnant or planning to be after age 35.

• Couples who already have a child with mental retardation, an inherited disorder or a birth defect.

• Couples whose infant has a genetic disease diagnosed by routine newborn screening.

• Women who have had babies who died in infancy or three or more miscarriages.

• People concerned that their jobs, lifestyles or medical history may pose a risk to outcome of pregnancy. Common causes of concern include exposure to radiation, medications, illegal drugschemicals  or infections.

• Couples who would like testing or more information about genetic conditions that occur frequently in their ethnic group.

• Couples who are first cousins or other close blood relatives.

• Pregnant women whose ultrasound examinations or blood testing indicate that their pregnancy may be at increased risk for certain complications or birth defects.

If you think you could benefit from genetic counseling, call your local chapter of the March of Dimes, or send an email to Askus@marchofdimes.org, for information on services in your area.

Screening for birth defects

Tuesday, September 9th, 2008

At my last prenatal appointment I had a combination of tests done to screen for birth defects such as Down syndrome and Trisomy 13 and 18. I was nervous going, but my husband was with me for support. My visit started with an ultrasound. The doctor rubbed a hand-held device (called a transducer) across my belly. The baby was face up and the doctor needed him/her to turn to the side in order to measure the thickness at the back of the neck (called nuchal translucency).  We waited and waited, but he/she wouldn’t budge. I certainly didn’t mind because I was able to admire the beautiful image on the screen longer.

After several minutes, the doctor finally called for a nurse. She brought me a very sweet orange drink and the doctor said he would be back in less than 10 minutes. I was thinking, “yeah right, this isn’t going to work.” Well, wouldn’t you know it. When he came back and put the transducer on my belly, there it was — the most perfect profile. I guess the baby just needed a little energy. Using the mouse on the ultrasound machine, he was able to measure the back of the neck.

Then I was passed off to the nurse who took a blood sample. I don’t know if this is always the case with maternal blood screening, but she pricked my finger and placed about 5 or 6 drops of blood on a card. The office sent the blood sample to a lab and I would get the results back in about four days. The lab calculated my risk of chromosomal birth defects, using the combined results of my blood test and ultrasound exam.

I received a call a few days later. I was told that based on my age, blood work and ultrasound my risk for Down syndrome was 1 in 1, 610 and my risk for Trisomy 18/13 was 1 in > 10,000. I know that no test can gaurantee the birth of a healthy baby, but I was so relieved. It’s always nice to here reassuring news. Waiting for test results can be so stressful.