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.
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.
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.
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.
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.
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.