For more information on AFP Tetra and testing procedures, call The Group for Women at 757-466-6350.
Down syndrome and trisomy 18 are conditions caused by chromosomal abnormalities. Chromosomes are present in every cell of the body and contain genetic information that helps determine how we look, how our bodies grow and develop, and our health. A developing baby normally receives 23 chromosomes in each cell. The chromosomes pairs are numbered 1 through 23. Sometimes a baby can be born with too many or too few chromosomes. Errors in the number of chromosomes may cause a variety of birth defects, ranging from mild to severe.
In Down syndrome, also called trisomy 21, a baby has an extra copy of the #21 chromosome. All babies with Down syndrome have some degree of mental retardation and often have physical abnormalities such as heart defects. About 1 in 800 babies is born with Down syndrome. 1 AFP Tetra 75% to 80% Down syndrome pregnancies.
Trisomy 18 is also known as Edwards syndrome. Babies with this condition have an extra copy of the #18 chromosome. Trisomy 18 causes severe mental retardation and physical abnormalities. Most babies with trisomy 18 die within the first year of life. Trisomy 18 is rare, occurring in 1 in every 7500 births.3 AFT Tetra detects 73% of trisomy 18 pregnancies.
Open neural tube defects, such as open spina bifida, occur when the baby’s spinal cord does not close completely during development. About 1 in 1000 babies is born with open spina bifida. 1,5 The effects of open spina bifida range from bladder control problems to paralysis and hydrocephalus. AFT Tetra detects 80% of pregnancies with open spina bifida.
What does it mean if my AFP Tetra screening is negative?
A negative test result significantly reduces the likelihood that your baby has Down syndrome, trisomy 18, or an open neural tube defect; however, screening tests can not completely rule out the possibility of these problems. Additionally, screening tests do not detect other chromosomal abnormalities or birth defects.
Does a positive AFP Tetra result mean my baby has a birth defect?
No. Screening tests cannot diagnosis problems with your baby or pregnancy. A positive test result can only tell you that your baby is at increased risk for having Down syndrome, trisomy 18, or an open neural tube defect. Typically, a woman who has a positive screening result is offered additional test to determine if the baby has one of these conditions.
If my test result is positive, what happens next?
Follow-up options are discussed between you and your doctor. If your screening test is positive, your physician may recommend one or more of the following.
- Genetic counseling. Genetic counseling is designed to help you understand your test results and follow-up options and may include a discussion of your family and pregnancy history. Genetic counseling may be provided by a certified genetic counselor, perinatologist (high-risk pregnancy physician), or your own obstetrician.
- Ultrasound. This procedure uses high-frequency sound waves and a computer to create images of the developing baby. In the second trimester, a detailed ultrasound examination of the baby may be able to identify some birth defects such as open spina bifida. Babies with Down syndrome and trisomy 18 may have certain features that can be seen on ultrasound, but, in general, neither can be diagnosed by ultrasound alone. Ultrasound is also used to measure the baby and determine how far along you are in your pregnancy (gestational age). The levels of the proteins measured in the AFP Tetra test vary with each week of pregnancy, so knowing the exact gestational age is an essential part of the test. If ultrasound dating changes your gestational age by 10 days or more, your physician may ask the lab to recalculate your test results. Ultrasound may reveal the presence of twins, which can also affect your AFP Tetra result.
- Non-Invasive Prenatal Test (NIPT): genetic testing using cell-free fetal DNA that circulates in maternal blood. The test can be done as early as 10 weeks of pregnancy to detect Trisomy 21 (Down syndrome) and many more chromosomal abnormalities. This test is only indicated for high risk pregnancies such as: personal or family history of aneuploidy, advance maternal age, an abnormal serum screen and/or abnormal ultrasound.
- Amniocentesis. This procedure is usually performed after the 15th week of pregnancy. Ultrasound is used to guide a thin needle through the abdomen into the uterus, and a small amount of fluid (amniotic fluid) from around the baby is removed. The cells in the fluid are examined in the laboratory to determine whether a chromosome abnormality like Down syndrome or trisomy 18 is present. Amniocentesis can diagnose most chromosomal abnormalities but cannot diagnose or identify all birth defects. Alpha-fetoprotein (AFP) is also measured in the amniotic fluid, and if open spina bifida is suspected, a spinal protein called acetylcholinesterase (AChE) is measured as well. This combination of tests can diagnose most, but not all, babies with open spina bifida.6
What is Maternal Serum Screening?
Maternal serum screening is a simple blood test offered in pregnancy to identify women who are at increased risk of having a baby with Down syndrome, trisomy 18, or an open neural tube defect such as open spina bifida.
What is AFP Tetra?
AFP Tetra is a maternal serum screening test that is offered between 15-21 weeks in pregnancy and measures the levels of four proteins in a women’s blood: AFP (alpha-fetoprotein), hCG (human chorionic gonadotropin), uE3 (unconjugated estriol), and dimeric inhibin A (DIA). Results of the blood test are combines with clinical information about you, such as your age and weight, to determine your baby’s risk for having Down syndrome, trisomy 18, or an open neural tube defect. If you are found to be at increased risk for having a baby with one of these conditions, follow-up testing will be offered.
Note: This material is provided for general information purposes only. It is not intended as a substitute for medical advice and/or consultation with a physician or technical expert.