Clinical Services

Introduction

Your doctor may have suggested that you consider having a blood test called the BEST Test. We would like to provide you with information about the nature of the test to help you understand its purpose.

Many pregnancies have normal outcomes, and it is appropriate for women to expect that their pregnancy will result in a normal, healthy baby. However, some risk exists for all pregnancies. Family history, maternal or paternal age, maternal illness, medication exposures during pregnancy, abnormal ultrasound findings, or other prenatal events may indicate added risk. The BEST Test offers an opportunity to define your risk for certain unexpected complications. When an increased risk is identified, it may help your doctor to manage your pregnancy more specifically.

Nature of the Test

The BEST Test is a blood test performed between 10 and 22 weeks of gestation. The test measures five chemicals in your blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), estriol (UE3), sex hormone binding globulin (SHBG), and pregnancy associated plasma protein A (PAPP-A). AFP is produced predominantly by the baby, while the placenta produces the other chemicals. The amount of chemicals changes with gestational age and other prenatal circumstances, but some patterns correlate with certain genetic disorders and birth defects.

The BEST Test is a powerful pregnancy management tool. It provides information about the pregnancy in regard to four major groups of disorders relating to the baby and placenta:
1. Down syndrome
2. Open body wall defects
3. Placental disorders
4. Other chromosome abnormalities or disorders

The purpose of the test is to shift attention to or from one of these groups. It is very important to realize that the BEST Test is a screening test, which means the results are not diagnostic for any particular disorder. The results of the BEST Test are usually available within two business days.

The BEST Test Results

The hoped for result from the BEST Test is, of course, to learn that any of the four major groups of disorders are quite unlikely, thereby gaining peace of mind. In most instances this is the case.

When the test results are reported as “abnormal”, this does not mean the baby has a problem. The BEST Test is designed to show “abnormal” results in about 3 percent of normal pregnancies. Therefore, an “abnormal” outcome of the BEST Test does NOT mean the baby is abnormal. It means that more testing may be needed to explain the results.

When the BEST Test results are reported as “abnormal”, it focuses attention on one of the four groups of disorders and away from the others. The implications from abnormal results vary with each group.

1. Down syndrome
The BEST Test gives a specific risk number for Down syndrome that can be compared with the risk based on maternal age alone. Down syndrome is a relatively common form of mental retardation, occurring in about 1 in 700 babies. Its frequency increases with the age of the mother. Over 80 percent of cases of Down syndrome are detected by the BEST Test, which is a substantial proportion but certainly not complete. In the BEST Test report, the risk for Down syndrome is indicated as increased when it is higher than 1 in 200.

2. Open body wall defects, including open neural tube defects (such as spina bifida)
These are disorders with incomplete formation of the brain, spine, abdomen, or other regions of the body. About 90 percent of such cases are indicated by the BEST Test. A normal test result is particularly valuable for excluding these types of birth defects. Closed spine defects and malformations of internal organs are not addressed by any screening method, and the BEST Test is not sensitive to neural tube defects before 12 weeks gestation.

3. Placental disorders
The BEST Test may provide results indicating an increased risk for placental disorders, which may lead to growth retardation of the baby or other complications. A normal BEST Test result correlates well with normal placental function and normal fetal growth for the rest of the pregnancy.

4. Other disorders
These disorders are very rare--much less common than Down syndrome. The BEST Test picks up a relatively high percentage of these disorders. Some, but not all, of the disorders are dependent on maternal age.

When the screen is abnormal, the pregnancy outcome is abnormal in 30 percent of cases. An abnormal BEST Test result flags a pregnancy at higher risk, alerting the doctor to monitor the patient more closely throughout the pregnancy. The BEST Test report includes specific recommendation for follow-up. When the BEST Test result is normal, the pregnancy outcome is normal 98 percent of the time. This means a normal BEST Test is very reassuring.

Follow-Up Studies

Follow-up of the BEST Test depends on the focus of the results. In many instances, a basic ultrasound examination reveals information to reconcile unusual test findings. In other instances, a detailed ultrasound examination and, possibly, chorionic villus sampling or amniocentesis will be considered.

A basic ultrasound examination can provide experienced doctors a resolution high enough to rule out the major birth defects from Group 2. Many disorders from Group 4 can often be eliminated by a detailed ultrasound examination. The placental disorders from Group 3 do not always look abnormal on ultrasound during early pregnancy, but may be detected by measuring the baby and doing blood flow studies by ultrasound at a later gestational age.

A detailed ultrasound examination is very helpful--but not diagnostic for Down syndrome. Most babies with Down syndrome show abnormal features on ultrasound, but a baby with Down syndrome can look normal. The study of placental cells obtained by chorionic villus sampling or fetal cells obtained by amniocentesis is diagnostic for Down syndrome, because it tells for sure whether the additional chromosome that causes Down syndrome is present or absent. The decision of doing a procedure is completely up to you.

Deciding to Test or Not

Most obstetricians support maternal serum testing and most patients accept it. However, there are important arguments for and against the testing and you should decide for yourself what is right for you. While the BEST Test involves a simple blood specimen, it is a powerful pregnancy management tool that provides significant information about your pregnancy, sometimes with far-reaching implications for you and your family. Therefore, your decision about whether or not to have this test is important. The purpose of this pamphlet is to give you information so that you know beforehand what to expect and can make an informed decision you are comfortable with. If you would like further information, please call (414) 475-7400 or (800) 647-0089 to speak with a Great Lakes Genetics genetic specialist.

Frequently Asked Questions

Many of my friends have had an abnormal maternal serum screen and their babies were fine. Why should I consider this test?
With any screening test there are such cases, but with the BEST Test false positives occur far less often. Most patients find the BEST Test reassuring. If the Best Test is abnormal, it helps your doctor follow the baby for specific possible conditions.

Why is the BEST Test the best maternal serum screen?
It is done early in pregnancy, it has a lower false positive rate, and it addresses more maternal, fetal and placental conditions than the other serum screens.

When can the BEST Test be done?
The BEST Test can be done from 10 to 22 weeks gestation.

Will the BEST Test tell me that I am having a normal baby?
No, the BEST Test cannot rule out Down syndrome or any other disorder. The BEST Test provides a risk assessment. A low risk or a very low risk (under 1 in 3,000) can often be reassuring and may prompt you to decide against further testing (such as CVS or amniocentesis).

How will I learn the BEST Test results?
The results will be provided to your doctor’s office.

What if the results are abnormal? Would re-testing be helpful?
Try to stay calm. Since the BEST Test is a screening test, this does not mean your baby is abnormal. First, talk to your doctor. Great Lakes Genetics is also here to help you; you are welcome to call us. Re-testing is not helpful because screening tests should lead to diagnostic tests, not further screening tests.