University of Nebraska Medical Center - Quad Fetal Risk Assessment

Print | PDF

Quad Fetal Risk Assessment

What is the Quad Fetal Risk Assessment?

The Quad Fetal Risk Assessment was developed to identify women who have an increased risk for having a baby with certain kinds of birth defects. Only 3 to 4% of babies are born with a birth defect. Many of these occur in situations in which couples have no reason to suspect that there may be a problem. This test may provide both you and your health care provider with information important for making decisions regarding the management of your pregnancy.

The Quad Fetal Risk Assessment isolates four proteins (from a small sample of the mother’s blood) called alpha-fetoprotein (AFP), estriol (uE3), human chorionic gonadotropin (hCG), and dimeric inhibin A (DIA). These proteins are normally made by the fetus as it develops and are passed into the amniotic fluid. The proteins are then transported through the placenta into the mother’s blood where they can be measured. The screen should be performed between 14 weeks and 20 weeks 6 days past the first day of the woman’s last menstrual period. These levels are compared to amounts normally present during pregnancy. Although the protein levels change significantly during the course of a normal pregnancy, it is predictable, and the health care providers use these results as well as a woman’s age, age of the fetus, the woman’s weight and race to calculate the risk of having a baby with problems. Abnormal values do not diagnose a specific defect but may identify pregnancies at a higher risk for a fetus with a birth defect such as an open neural tube defect (spina bifida), an abdominal wall defect, or a chromosome problem such as Down syndrome. If this calculated risk is determined to be "significant," additional testing, including detailed ultrasound, amniocentesis, and genetic counseling may be indicated to provide additional information about the baby. In most cases, the screen will be negative and no other tests will be necessary. Although this is reassuring, it does not rule out all birth defects. For most cases with an initial positive screen, additional information gathered by your health care provider may help them take better care of your pregnancy and reassure everyone that the pregnancy is progressing as it should. The recent addition of DIA has reduced the number of false-positive screens from 4.7% to 2.9%.

What if the Quad Fetal Risk Assessment suggests an increased risk for Neural Tube Defects?

Elevated AFP levels can be seen in several conditions such as neural tube defects (NTD), pregnancies farther along than expected, more than one baby, and babies with certain other complications.

Neural Tube Defects

A neural tube defect (NTD) is an abnormal opening of the skull or spine resulting from a developmental difficulty very early in pregnancy. One or two babies in 1,000 are born with an NTD with no prior family history. When there is a family history of NTD or an exposure which increases risks for NTD, more direct forms of prenatal diagnosis may be indicated.

The Quad assessment will identify 85% of all pregnancies involving an open neural tube defect. This early warning permits health care providers and families to plan for appropriate management at delivery and after birth.

If gestational age, presence of one baby, and no observable problems are confirmed by ultrasound, the health care provider may suggest repeating the test. Slightly less than 3 out of 4 (70%) women who have a repeat test will have values within the normal range and no further testing will be indicated. This repeat sample is typically collected approximately one week following the initial sample. Approximately 1 out of 100 women (1%) will have a screen that continues to show an increased risk for a neural tube defect (elevated AFP). These women will be offered amniocentesis to help collect more information regarding the pregnancy.

Underestimated Gestational Age

Establishing the correct gestational age is important when decisions need to be made regarding premature labor or inducement of labor. Other obstetrical complications detected by the Quad assessment can be managed more effectively when identified early in pregnancy.

The Presence of Twins

An elevated level is seen in multiple gestations. Ultrasound can also show that there is more than one baby present. This information allows the mother-to-be and health care provider to take additional precautions and to prepare for a more complex delivery.

Other Defects

Defects of the abdominal wall which affect the intestines and internal organs may also be discovered. Advance notice allows families and medical professionals to prepare for appropriate management at delivery including surgery shortly after birth.

What if the Quad Fetal Risk Assessment suggests an increased risk for Down syndrome?

Quad assessment alerts doctors to 60-80% of babies with Down syndrome. Down syndrome (trisomy 21) is the most common genetic cause of mental retardation, occurring in approximately 1 in 750 births. Individuals with Down syndrome have mild to profound retardation and may have other physical or medical problems including heart defects. This screening test identifies a pregnancy at risk for Down syndrome but further testing is necessary to diagnose this condition.

A positive screen for Down syndrome occurs when the risk for Down syndrome calculated by using the AFP, uE3, hCG, DIA, maternal age, fetal age, and race suggests that the risk of Down syndrome is greater than a woman 35 years old and thus is greater than the risk of amniocentesis.

If your Quad assessment identifies an increased risk for Down syndrome, your health care provider will recommend that ultrasound be done. If the ultrasound changes your dates significantly, your risk for Down syndrome will be recalculated. Ultrasound is helpful to evaluate the gestational age and physical structure of the fetus. It cannot, however, rule out Down syndrome. In some cases, the ultrasound will show that the gestational age is less than originally thought and the screen will indicate that you no longer have an increased risk for Down syndrome. In other cases, the ultrasound will suggest that your blood test was drawn prior to the time when it can be accurately interpreted (14 weeks gestation) and the test will be repeated at the appropriate time. Only about 3 in 100 (3%) women will have a value that continues to suggest an increased risk for Down syndrome. In these pregnancies, amniocentesis would be recommended to rule out Down syndrome or other chromosome abnormalities.

Increased Risk for Other Problems

The values obtained from the Quad assessment may reveal an increased risk for other problems that are less common. Again, because this may change how you and your health care provider manage the pregnancy, additional testing may be recommended. Ultrasound and amniocentesis may be discussed.

Summary

In most cases, this screening test will reassure you and your doctor that the pregnancy is progressing as it should. In the event of an abnormal result, you and your health care provider may decide to obtain more information about the fetus to decide how to manage the pregnancy. Other health care professionals are also available to provide you with more information in order to prepare you to make these decisions.

For more information regarding this test or the results, contact the Hattie B. Munroe Center for Human Genetics, Munroe-Meyer Institute (402) 559-5070 or 1-800-656-3937, FAX# (402) 559-9463, and TDD# (402) 559-8638.

To send a specimen, print out the Quad Fetal Risk Assessment Form.

Other Prenatal Diagnostic Options

Human Genetics Laboratory