Prenatal Testing & Care

Chorionic villus sampling (CVS) is a test that can detect chromosomal abnormalities such as Down syndrome and a host of other genetic disorders in a developing fetus. The test is offered to women who are likely of having a baby with these disorders or because they or their partner have a genetic disorder. CVS provides much of the same information as an amniocentesis but can be done about a month earlier, between 10 and 12 weeks of pregnancy.

CVS involves getting a very small sample, or biopsy, of the chorionic villi cells in the placenta and sending it to a lab for genetic analysis. The genetic material in chorionic villi cells – DNA, chromosomes, and enzymes - is the same as that in the baby's cells.

• Chromosomal defects such as Down syndrome, trisomy 13, trisomy 18, and sex chromosome abnormalities like Turner syndrome and Klinefelter syndrome; the test is more than 99 percent accurate in diagnosing these conditions.
• Genetic disorders such as Tay-Sachs disease, hemophilia, sickle cell disease, or cystic fibrosis.
• The sex of your baby if you might have a gender-related genetic disorder such as hemophilia, which a mother only passes to her male children.
• Unlike amniocentesis, CVS cannot detect neural tube defects such as spina bifida. The test can also not check the development of the baby's lungs.

The Integrated Screening Test tells you what the chances are that your baby might have Down syndrome or open neural tube defects such as spina bifida. There are different ways to test for Down syndrome screening but the Integrated Test is the most specific, has the highest detection rate and a low false-positive rate.

1. The first stage is ideally done between 11 and 12 weeks of pregnancy, but any time between 10 and 13 weeks is acceptable.

• One of our genetic counselors will meet with you, review your medical history and explain the test.
• We will perform an ultrasound to precisely determine how far along you are in your pregnancy and to measure the thickness of your baby's nuchal translucency (NT), which is a fluid-filled space at the back of the baby's neck.
• A nurse will take a blood sample to measure the amount of pregnancy associated plasma protein-A (PAPP-A).

1. The second stage is ideally performed at 15 or 16 weeks of pregnancy and no later than 22 weeks.

• A nurse will take a second blood sample to measure the amount of four proteins in your blood – alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin-A (inhA).

We combine the results from the first and second stages into a single screening result. The NT measurement, the levels of the five substances in your blood and your age help us estimate your risk of having a baby with Down syndrome. We can also use the screening results to estimate the risk for other disorders including open neural tube defects (spina bifida) and Trisomy 18.

The integrated screening results are usually ready one week after the second stage. We send a copy of the test results to your physician and a genetic counselor will call you to discuss the results and schedule any necessary follow-up appointments.

What does a positive result for Down syndrome mean?

Your integrated screening results are considered "screen positive" if the risk for Down syndrome is one in 110 or greater (for example, 1 in 90 or 1 in 80). If your results are "screen positive," your baby has a higher risk for Down syndrome than other babies. We will then offer you an amniocentesis test to examine your baby's chromosomes.

It's important to note that five out of every 100 women who take the integrated screening test receive "screen positive" results but most will not have a baby with Down syndrome.

What does a negative result for Down syndrome mean?

Your integrated screening results are considered "screen negative" if the risk for Down syndrome is less than one in 110 (for example, 1 in 150 or 1 in 200).

Note that screening tests cannot diagnose or rule out specific conditions so a screen negative result does not mean your baby will not be born with Down syndrome, it means that the chances are low.

What is Down syndrome?

Down syndrome, also called trisomy 21, is the most common chromosomal abnormality in newborns, occurring in about one of every 700 births. Normally, a person has 46 chromosomes, each of which is made up of thousands of genes, which are located inside all cells in the body. Genes direct all the cells' activities, including growth, development, and body functions. Each child inherits 23 chromosomes from the mother and 23 from the father, for a total of 46.

In most cases of Down syndrome, there is an extra copy of chromosome 21, giving that person 47 chromosomes instead of the usual 46. There are also rare cases when a parent carries a subtle abnormality on chromosome 21 that is passed to a child and causes Down syndrome. Children born with Down syndrome typically have moderate to severe developmental disability, a characteristic physical appearance (flat face, slanting eyes), and other health problems. Life expectancy for a person with Down syndrome is about 50 years.

Down syndrome may affect any pregnancy but some women are at higher risk than others, including those who:

• Are older.
• Have had a baby with Down syndrome already.
• Have abnormalities involving chromosome 21.

Genetic Amniocentesis is a test of the amniotic fluid surrounding your unborn baby in the uterus. Amniotic fluid contains fetal cells and chemicals produced by the baby that, when analyzed, can help determine certain types of birth defects.

Genetic amniocentesis poses a small risk for you and your baby, so it is generally only offered to women who have a significant likelihood of genetic disorders.

That includes women who:

• Have an abnormal ultrasound or another prenatal screening test.
• Have a family history of certain birth defects or you or your partner is a known carrier of a genetic disorder.
• Have already had a child with a birth defect.
• Are 35 years of age or older.
• Have a suspected uterine infection or Rh incompatibility.

The test is usually performed between 16 and 18 weeks of pregnancy, and can be used to find:

• Down syndrome.
• Sickle cell disease.
• Cystic fibrosis.
• Muscular dystrophy.
• Tay-Sachs disease.
• Certain neural tube defects such as spina bifida and anencephaly.

Before an amniocentesis, an ultrasound will be done to measure the size of the developing baby, the gestational age, the position of the baby and the placenta, and to be sure there is enough amniotic fluid

The Procedure

You will meet with our genetic counselor before the amniocentesis. The counselor will explain the procedure, the risks involved, and possible results.

Guided by ultrasound, the physician will locate the fetus and placenta and then insert a thin, hollow needle through your abdomen and the wall of your uterus, into the amniotic sac but not too close to the baby. The physician will then take a sample of the fluid surrounding the baby into a syringe attached to the needle. The fluid is sent to the lab for a variety of tests that will give us more information about your pregnancy.

Amniocentesis may cause some of the baby's blood cells to enter your bloodstream. If you have Rh-negative blood, you will have blood taken before the procedure and will also receive a shot of Rhogam afterward to prevent you from producing antibodies against your baby's blood cells.

After Amniocentesis

You may experience:

• Some tenderness where the needle was inserted.
• Some minor cramping (less than a menstrual period).

There is a slight risk of miscarriage, infection and amniotic fluid leakage as a result of the procedure. If you develop a fever or have bleeding, vaginal discharge, or severe abdominal pain after your amniocentesis, please call your health care provider.

What do normal results mean?

A normal amniocentesis result means there are no signs of any genetic defects in your baby. Please note, however, that the test could miss some genetic defects. One of our genetic counselors will call you with the result of the amniocentesis.

What do abnormal results mean?

If your amniocentesis results are abnormal, it may be a sign of more than 200 disorders, including Down syndrome, hemoglobinopathies, and Tay-Sachs disease. If the amniocentesis results are abnormal, our genetic counselors will meet with you to carefully and completely explain what the results mean.

Ultrasound is a common test during pregnancy that uses high frequency sound waves to look at the anatomy and structures of the developing baby. Ultrasound machines don’t use radiation and cause no known physical or chemical changes that could affect your baby.

Sometimes, we must pay particular attention to certain parts of the baby’s anatomy, especially if there is concern about fetal problems based on other tests, on your medication or medical condition, or based on your family history. This specialized ultrasound is called a Level II or targeted ultrasound and is usually performed between 18 and 22 weeks.

The Procedure

The first phase of the Level II ultrasound is conducted by a trained ultrasound technologist. One of our physicians will then complete the study. Using an instrument called a transducer that is moved over your abdomen, the technologist or physician will measure your baby to see how far along your pregnancy is and to ensure that your baby is growing on schedule. The clinicians will then view the heart, the kidneys, bladder, stomach, brain, spine, arms, legs, umbilical cord and reproductive organs to make sure they are developing normally. They will also look at your amniotic fluid levels, the location of the placenta, and the fetal heart rate. We will explain all the results of the ultrasound to you and your family before you leave and we’ll also send them to your health care provider. If we do find something out of the ordinary on the ultrasound, we’ll explain it carefully and completely, and we’ll schedule time for you to meet with one of our genetic counselors so that you have every opportunity to understand what we’ve found. We can also help make appointments with other specialists if their expertise will be helpful.

Ultrasound is a common test during pregnancy that uses high frequency sound waves to examine the anatomy and structures of the developing baby. Ultrasound machines emit no radiation and have never been shown to produce any known physical or chemical changes that could affect the developing baby.

Sometimes, particular attention may be directed to certain portions of the developing baby's anatomy, especially if there is a concern about certain types of fetal problems based on other tests or family history. This specialized ultrasound examination is called a Level II ultrasound or targeted ultrasound and is usually performed in mid-pregnancy. At the Prenatal Diagnosis Center a qualified ultrasound technologist performs the first part of the study, and then one of our physicians completes it. The results of the ultrasound examination will be explained to the patient and her family before she leaves the unit. Results are relayed to the patient's health care provider the day of the ultrasound.  

A targeted ultrasound is useful in determining the size and position and internal anatomy of the fetus, but there are limitations. Some abnormalities may not be detected until later in the pregnancy, or not at all.  

The Prenatal Diagnosis Center staff makes resource information and literature about targeted ultrasound available to patients and their families. Please call us with your questions and requests for further information. We can be reached by calling the Prenatal Diagnosis Center at (401) 453-7510.