Genetic, Diagnostic, and Screening Tests

Genetic tests are used to look for certain genetic diseases, chromosome problems, or birth defects. As your pregnancy progresses, you will have many choices for genetic testing. Deciding which (if any) of these tests are right for you and your partner can be difficult. Factors such as your age, family and medical history, and environmental exposures should be considered as you make these decisions.

Some important questions to ask include:

• What risk factors do we have that increase our chances of having a baby with a chromosome problem?

• What information will this test give us?

• How accurate is this test?

• Are there any risks for me or my baby if I have this test?

• Will we do anything differently if the test comes back abnormal?

Genetic testing is a very personal decision that can affect the management of your pregnancy and help you choose the safest place for birth. If you feel you might desire these tests, let us know. They are never required, but available to any client who wants them. We can also refer you to the hospital Genetics Department for genetic counseling and possible testing. Most chromosome disorders are associated with major birth defects.

The general risk of having a child with a major birth defect is about 2-3%. Although birth defects can be caused by exposure to harmful substances or medications, the cause is unknown in 70% of cases.

Any person can have a baby with a chromosome disorder, but birthing parents who are older have a higher risk. The approximate risks are:

Age Risk of Down syndrome Risk of any genetic disorder

20 1 in 1,667 1 in 526

25 1 in 1,250 1 in 476

30 1 in 952 1 in 385

35 1 in 378 1 in 192

38 1 in 173 1 in 102

40 1 in 106 1 in 66

42 1 in 63 1 in 42

45 1 in 30 1 in 21

There are two types of genetic testing. Some genetic testing is considered diagnostic, while others are only a screening test. Screening tests and diagnostic tests are not equal – it is important to understand the difference between the two types of testing.

CVS testing is usually done from the 10th through 13th week of pregnancy. It is important to know that not all birth defects can be detected by CVS. A small sample of cells is taken from the placenta. These cells have the same chromosomes as the baby. The procedure takes about one hour to perform. There is a small risk of bleeding, infection, or miscarriage after the procedure. When CVS is done in an experienced center, the risk of miscarriage as a result of the CVS is about 1 in 1,000.

Amniocentesis is usually done between the 16th and 18th week of pregnancy. A needle is inserted through your belly to remove a small sample of amniotic fluid. This fluid has some of the baby’s cells in it. An ultrasound is done at the same time so that the baby is not harmed during the test. There is a small risk of bleeding, infection, or miscarriage after the procedure. The risk of miscarriage is approximately 1 in 1,000. Results are usually available within two weeks.

Non-invasive prenatal testing is a newer form of genetic screening that looks for an increased risk for Down syndrome, Trisomy 18, Trisomy 13 (another chromosomal abnormality with similar outcomes as Trisomy 18), or changes in the number of sex chromosomes. It also determines the baby’s sex.

Currently, this screening test is typically covered by insurance for women who are 35 or older, or who have a family history of one of the conditions screened for. The test detects the baby’s DNA in the mother’s blood stream. It does not take the place of amniocentesis or CVS, but has high detection rates and lower false-positive rates than the other screening tests available. If you are interested in this test, the CNM will refer you to the genetics department, so they can determine which brand of test is best for your insurance.

The first trimester screen is a test that measures your baby’s risk for Down syndrome or Trisomy 18. The test is performed between the 11th and 14th week of pregnancy and combines information from an ultrasound and a blood test for the mother.

Most people are familiar with Down syndrome. Trisomy 18 is a chromosomal abnormality that affects about 1 in 5,000 live born infants per year. Due to the presence of many serious complications, about 5-10% of children survive past the first year, and those that do are often affected by severe intellectual disability.

The ultrasound part of the test is performed by a certified technician and measures the amount of fluid in the back of the baby’s neck. All developing babies have some fluid in the back of the neck, but babies with chromosome problems tend to have higher than average amounts. Since babies without chromosome problems can also have extra fluid at the back of the neck, the blood test is needed for complete interpretation.

The blood test measures the amount of two substances (PAPP-A and beta hCG) that are normally found in a pregnant person’s blood stream. The ultrasound and the levels of these substances are combined with specific information about you such as your age, weight and race to determine if your baby is at an increased risk for Down syndrome or Trisomy 18.

This test identifies about 85% of babies with Down syndrome. If your results show that your baby is not at an increased risk for Down syndrome or Trisomy 18, it means that the risk for these problems is low but not zero. If the result is negative, there is still a small chance that your baby could have Down syndrome, Trisomy 18, or another chromosome problem.

If your results show that your baby is at an increased risk for Down syndrome or Trisomy 18, it does not mean that your baby will have a health problem. It simply means that the risk is higher than average and you will be given the option of additional testing to study the baby’s chromosomes. Depending on the age of your pregnancy, testing options may include chorionic villi sampling (CVS) and/or amniocentesis. These tests are the only way to know with 100% certainty if your baby has a chromosome problem before birth. Most women who are identified as “increased risk” will have a healthy, normal baby.

The quad screen is a blood test offered to all pregnant people around 16-18 weeks of pregnancy. It screens for Down syndrome, Trisomy 18, and open neural tube defects. By measuring the levels of four substances in the birther’s blood, the quad screen can identify about 80% of fetuses with Down syndrome, 60% of Trisomy 18, and 85% of neural tube defects. The chemicals measured are: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin-A. Abnormal test results can also indicate a higher risk for other pregnancy complications, such as premature labor, fetal-placental bleeding, fetal distress, or preeclampsia. An undiagnosed twin pregnancy or an incorrect due date can make the test results inaccurate.

The AFP test is a component of the quad screen that can be tested separately between the 16th and 18th week of pregnancy. When measured alone, it can identify fetuses with open neural tube defects. It is measured alone typically if a pregnant person has a first trimester screen and desires more screening, as the first trimester screen does not screen for neural tube defects. It can also be ordered if a family history is present and no other testing is desired. Neural tube defects affect about 3,000 pregnancies per year in the U.S.

The most common form of a neural tube defect is Spina Bifida. This is caused when the tiny bones of the spine don’t close and a part of the spinal cord slips through the vertebrae. This can be corrected with surgery before or after birth. Children with Spina Bifida can have mild to severe forms, with few problems to paralysis and inability to control bowels and bladder.

Other less common but more serious forms of neural tube defects are anencephaly and encephalocele. Anencephaly means the baby is missing part of its brain or skull and these babies usually do not live more than a few hours after birth. An encephalocele, a rare disorder, is an opening in the skull requiring surgery after birth that is associated with other serious complications.

Although we offer this test to all pregnant clients, it is important to understand that it is a screening test. An abnormal test result would not necessarily mean that any of the above conditions are present. It simply means that the risk is higher than average and you will be given the option of additional testing to study the baby’s chromosomes. Depending on the age of your pregnancy, testing options may include chorionic villi sampling (CVS) and/or amniocentesis. These tests are the only way to know with 100% certainty if your baby has a chromosome problem before birth. Most people who are identified as having an “increased risk” will have a healthy, typical baby.

Integrated Screening (or Sequential Screening) is a genetic screening option for those who are interested in both first and second trimester screening tests. Integrated screening is a method where results are not reported until after the second trimester test results are obtained.

There is a better detection rate for genetic disease than with either the first or second trimester screens alone, but the downside is that mothers have to wait until later in the pregnancy to find out results. There is an option for what is called “Sequential Screening” where an abnormal first trimester result is reported so that the mother may pursue diagnostic testing if desired. Due to complexity of these screening test options, interested clients will be referred to the genetics department at Magee or hospitals within the Allegheny Health Network system for a genetics consult and scheduling.

The American College of Obstetricians and Gynecologists (ACOG) has established guidelines for offering cystic fibrosis (CF) screening to the general population. It is now recommended that CF screening be offered to all people of reproductive age, preferably before conception. The decision whether or not to be screened for CF is a very personal one. The test can be done with a simple blood sample or with a swab inside the mouth at The Midwife Center.

In Pennsylvania, all babies are tested for Cystic Fibrosis after birth as part of the Newborn Screen. You will know if your baby has this condition after they are born. There is nothing that can be done to correct it prenatally.

CF is a genetic disease that affects approximately 1 in 2,500 babies born in the US. It affects many organs of the body, especially the lungs, pancreas and digestive tract. It is characterized by thick mucus that coats the cells. The symptoms of CF vary from one person to another, but they usually lead to problems with digestion and breathing. People with CF have a shortened lifespan – the average life expectancy is 37 years.

Approximately 1 in 29 Caucasians are carriers of the CF gene. Although there are more carriers in the Caucasian population, CF can affect people of all races and ethnicities. Almost always, both parents must be carriers for a baby to be born with CF.

A positive result means that an individual is a carrier for CF. If one member of a couple is found to be a carrier it is recommended that the partner be tested. If both parents are carriers, the risk for having a child with CF is 25% with each pregnancy. The risk that the baby would be a carrier is 50%, and the chance the baby would be unaffected at all is 25%. If both parents are carriers, additional testing would be available, including amniocentesis or chorionic villi sampling to determine if the developing baby has CF. If the child is found to have CF, genetic counseling is available to provide information, support, and to help locate community resources for the family.

A negative result means that the individual is not likely to be a carrier for CF. More than 1,400 CF mutations exist. The screening test for CF is unable to test for all mutations, but it does test for the most common ones. This means that even with a negative result, an individual could be a carrier of a less common CF mutation.

Cystic Fibrosis screening is often covered by insurance. If you desire testing, you should contact your insurance provider to verify coverage and determine the portion of the cost that may be your responsibility.

Ultrasounds are offered to all pregnant people, regardless of age, to look at the fetal anatomy between 18-20 weeks of pregnancy. This is the second trimester ultrasound desired by most clients, to look at all the baby’s anatomy (heart, brain, spine, kidneys etc). If the parents wish, it can also determine if the baby is a boy or a girl. The ultrasound technician will always ask if this is desired. It is not an automatic part of the scan.

The fetal anatomy scan is not a medically indicated test. It is optional and may not be desired by everyone.

There are medically indicated ultrasounds. A few examples of reasons why an ultrasound would be medically indicated are unexpected size for dates, bleeding, post dates pregnancy or follow up to an abnormal finding. The midwives would discuss this with you during the course of your care.

Ultrasounds have many benefits, including: looking at placental location, confirming dates, diagnosing multiples, and detecting major anomalies that would determine a different prenatal care plan and delivery site.

There are no known harms to baby due to ultrasound.

Ultrasound does have some limitations. There is a margin of error, and a perfect ultrasound does not guarantee that your baby doesn’t have any genetic conditions or problems.

On the contrary, there are a few things that can be detected on ultrasound that can cause worry for parents and are typically normal variations:

1. Echogenic intracardiac focus (EIF): this means that when the ultrasound was looking at the heart, there was a bright spot. It is thought that this spot looks brighter due to calcium deposits, but its not certain what causes it. It does NOT cause any problems with how the heart functions, and is seen in 3-5% of normal pregnancies. Some studies have shown a very small increase in the risk for Down syndrome if an EIF is seen, however not all studies confirm this. It is considered a “soft marker” for Down syndrome, and in the absence of any other abnormal findings, the EIF is most likely a normal variant. If this is seen on your ultrasound, the midwife will offer you genetic screenings. This finding does not worry us, and is not meant to worry you, but in the case that you would want to proceed with testing we want to make sure it is available to you. We do not re-scan to evaluate the EIF later, as it doesn’t change and doesn’t affect the baby’s heart.

2. Choroid plexus cysts: This is another finding that can cause concern for parents. Choroid plexus cysts are found in the ventricles of the brain. They do NOT affect brain functioning and almost always resolve (it doesn’t mean anything if they don’t!). It is reported because they are a “soft marker” for Trisomy 18. These cysts are found in up to 3.6% of all fetuses in the second trimester and most often times are normal variants. Several large studies found no cases of Trisomy 18 when choroid plexus cysts were the only finding on ultrasound, but again, due to the association with this genetic condition, the midwife will offer genetic testing in the case that you may want more information. We don’t re-scan these cysts if they are present, because again, they often resolve and it doesn’t mean anything if they don’t resolve.

3. Placenta Previa (on first trimester ultrasounds): It is common to find a placenta previa on a first trimester ultrasound. This is where the placenta covers the cervix. If you have not had any bleeding, there is no reason to worry about this finding. The placenta will be re-evaluated in the second trimester and is most likely going to move up and out of the way by then. We aren’t concerned about placenta previa until the second half of pregnancy.