Posts Tagged ‘Down Syndrome’

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.

Blood test vs. amniocentesis

Thursday, January 13th, 2011

blood-testsResearchers are working on a new blood test that has the potential to diagnose Down syndrome in women who are at high risk for having a baby with this condition. If proven successful, this test might eliminate the need for the more invasive and risk-related tests of amniocentesis and chorionic villus sampling (CVS).  Both amniocentesis and CVS carry a risk of miscarriage.

A study conducted at the Chinese University of Hong Kong and recently published in the British Medical Journal (BMJ), included 753 pregnant women. Of these, 86 women were carrying a fetus with Down syndrome. There were no false-negative results with the new test. All babies with Down syndrome were detected. The study authors state that “If referrals for amniocentesis or chorionic villus sampling were based on the sequencing test results, about 98% of the invasive diagnostic procedures could be avoided. “

Further evaluation of this technology needs to be conducted before it is offered to the public, but this is exciting and hopeful science.  While the test won’t be available for at least another year, and the cost may be high, and currently it tests only for Down syndrome and not other conditions, it holds promise for the future.  It will be a new and safe screening tool to help us gather information about our developing babies.

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.

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.