Like the alphafetoprotein test, the triple screen test is a simple non-invasive blood test that is used to detect fetal abnormalities during the early stages of pregnancy.
Although it has the same ability to detect neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions., the alphafetoprotein triple screen uses three markers that increase its ability to detect Down's syndromeA congenital abnormality in which the baby is born mentally retarded, with an average IQ of 50 - 60 and with physical deformation of the face (low set ears, sloping forehead, mongoloid eyes), and shortness of stature.
Downs syndrome is caused by an extra chromosome 21 present in the G group. In a small percentage of cases it can be caused by the switching of chromosomes 14 or15 in the D group or chromosome 21 or 22.
Down's syndrome occurs in about 1 in 650 births, and is more commonly associated with children of mother's over the age of 35. Incidence in children of mothers over the age of 40 can be as high as 1 in 80.
Down's syndrome can be detected prenatally through amniocentesis. The mortality rate is high within the first few years. Down's syndrome is also known as mongolizm, trisomy 21 or trisomy G syndrome.
Visit our comprehensive glossary for more pregnancy terms and definitions..
The alphafetoprotein triple screen measures levels of alphafetoprotein, human chorionic gonadotropinHuman chorionic gonadotropin is a hormone released into the maternal bloodstream by the developing placenta from about six days after the last period was due (about 22 days after the last menstrual period). Its presence can be detected in the urine by a home pregancy test and a positive result indicates pregnancy. Gonadotropins are used to treat infertility, hypogonadism and nonobstructive cryptorchidism. Often abbreviated to HCG.
Visit our comprehensive glossary for more pregnancy terms and definitions. and unconjugated estriolA natural human estrogen that is found in the urine and blood. Measurement may be taken during the last trimester to determine the effectiveness of the placenta.
Visit our comprehensive glossary for more pregnancy terms and definitions. present in the maternal bloodstream.
Alphafetoprotein is a compound known as glycoprotein. It is manufactured first by the embryo's yolk sacThe structure that is attached to the embryo and provides initial nourishment until about the 7th week when it disappears.
The cells of the yolk sac (extraembryonic mesoderm) differentiate to develop early blood cells including the endothelium, primitive plasma and hemoglobin.
Visit our comprehensive glossary for more pregnancy terms and definitions., then later by the fetal liver. Alphafetoprotein is an important carrier of molecules in the fetal bloodstream. Between week sixteen and week twenty four the levels of alphafetoprotein double every five weeks and traces appear in the mother's bloodstream. Alphafetoprotein levels alone are responsible for detecting neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions. and the results are the same as the maternal serum alphafetaprotein test.
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Human chorionic gonadotropin (hCG) is a hormoneA complex chemical substance created in a part or organ of the body. When released it initiates or regulates activity in an organ or group of cells in another part of the body.
Hormones secreted by endocrine glands are transported through the bloodstream to their target organ. The amount of hormone secreted is regulated either by other hormones, by neurotransmitters, or simply when an excess of the organ's activity indicates a need to reduce the amount of the hormone produced.
Other hormones are produced locally by the organs themselves and are common in the digestive tract.
Visit our comprehensive glossary for more pregnancy terms and definitions. that exists only in pregnancy and is manufactured by the placentaThe placenta is a large disk shaped membrane responsible for providing nourishment to the fetus during pregnancy. It consists of three parts, the fetal part made up from the chorion membrane surrounding the fetus, the maternal part, formed from the decidua basalis layer of the uterine lining, and the intervillous space between the two plates. It is connected to the fetus by the umbilical cord and consists of tissue from both the mother and the embryo.
Its function is complex. It has been described as a simple organ that combines the functions of a kidney-dialysis machine, heart and lung machine and intravenous drip. It consists of enormous numbers of blood vessel branches that permit the exchange of nutrition and oxygen, from the mother's bloodstream to the fetus and the removal of wastes to the mother to be excreted. The placenta's remarkable quality is that it does so without the blood of the mother mixing with that of the baby.
It also is responsible for the production of vital hormones including, estrogen, progesterone, and human chorionic gonadotropin. After birth, the placenta is delivered, and is sometimes referred to as the afterbirth.
Visit our comprehensive glossary for more pregnancy terms and definitions.. It is responsible for controlling many of the functions that occur during the early stages of pregnancy. Higher than normal values of hCG are found in Down's syndromeA congenital abnormality in which the baby is born mentally retarded, with an average IQ of 50 - 60 and with physical deformation of the face (low set ears, sloping forehead, mongoloid eyes), and shortness of stature.
Downs syndrome is caused by an extra chromosome 21 present in the G group. In a small percentage of cases it can be caused by the switching of chromosomes 14 or15 in the D group or chromosome 21 or 22.
Down's syndrome occurs in about 1 in 650 births, and is more commonly associated with children of mother's over the age of 35. Incidence in children of mothers over the age of 40 can be as high as 1 in 80.
Down's syndrome can be detected prenatally through amniocentesis. The mortality rate is high within the first few years. Down's syndrome is also known as mongolizm, trisomy 21 or trisomy G syndrome.
Visit our comprehensive glossary for more pregnancy terms and definitions. pregnancies.
Unconjugated estriol (uE3) is a hormone that is synthesized by the fetal liver and adrenal glandsGlands which are located on each of the kidneys. The adrenal glands consist of two parts with distinct functions.
The adrenal cortex secretes cortisol and androgens when the anterior pituitary releases the production of adrenocorticotropic hormone (ACTH). Androgens are converted by the liver to the hormones testoterone and estrogens.
The adrenal medulla creates the cathecolamines epinephrine and norepinephrine.
Visit our comprehensive glossary for more pregnancy terms and definitions.. Reduced levels of estriol have been found in Down's syndrome and other pregnancies with a high somatic chromosomeOne of the structures within the nucleus of a cell that transmits genetic information. Each of the chromosomes contains a double strand of the helical nucleoprotein deoxyribonucleic acid (DNA). Chromosomes occur in 23 pairs in every human cell.
Visit our comprehensive glossary for more pregnancy terms and definitions. count.
The results of all three markers in combination can be used to more accurately determine the presence of a Down's syndrome pregnancy, although the ability to detect neural tube defects remains the same.
The alphafetoprotein triple screen is a voluntary test and its administration will depend on local practice. It is most frequently offered to women over the age of 35 or those who are at most risk of Down's syndrome.
You should take the test if you are interested to find out whether you are carrying a Down's syndrome baby. You should remember that many Down's syndrome babies are born to women under the age of 35, the age when amniocentesis or chorionic villus sampling (CVS) is offered.
Bear in mind that neither a regular alphafetoprotein test, nor the triple screen offers any conclusive results about the development of the fetus. It simply indicates whether more specific and possibly invasive testing is required.
There are few, if any, risks associated with this test.
The alphafetoprotein triple screen test may be performed any time between week fifteen and week twenty three. The most accurate results are achieved when it is done during week sixteen.
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The alphafetoprotein triple screen is read very much like the maternal serum alphafetoprotein test. Low levels of alphafetoprotein may indicated the presence of chromosomal abnormalities such as Down's syndrome. High levels of alphafetoprotein may indicate the presence of neural tube defects such as anencephalyA congenital defect in which the brain and spinal cord are absent, the cranium remains open and the vertebral canal stays grooved.
Anencephalic defects are transmitted genetically and can be detected early in the pregnancy by amniocentesis and ultrasonic testing. Anencephaly is not compatible with life. See also, neural tube defect.
Visit our comprehensive glossary for more pregnancy terms and definitions., a condition in which a part of the fetal skull is missing and is not compatible with life. High levels of alphafetoprotein leaking out of a defective spinal cord may also indicate spina bifidaA relatively common birth defect in which the spine fails to form properly leaving the spinal cord exposed. Spina bifida can result in mental disability and partial paralysis. Also called spinal dysraphia.
Visit our comprehensive glossary for more pregnancy terms and definitions. an opening which can be surgically repaired, although it may result in paralysis below the waist.
High levels of alphafetoprotein may be the result of many causes including a multiple pregnancy or a gestational age that is farther along than previously thought. The advantage offered by the alphafetoprotein triple screen over the maternal serum alphafetoprotein test is that it uses the two additional markers of human chorionic gonadotropin (hCG) and unconjugated estriol (uE3) to increase the accuracy of Down's syndrome screening. The test can detect Down's syndrome about 60% of the time, a rate that is about three times higher than the standard maternal serum alphafetoprotein test.
The result you are given will be most likely in the form of a risk ratio. This is computed using a number of risk factors including your age. If your risk ratio is 1 in 35 your chances of having a baby with Down's syndome is one out of thirty five deliveries. Your doctor will help you interpret the risks and determine your next course of action. For instance if you are 45 years old, the age specific odds for Down's syndrome are 1 in 25 so your chances are better than average and you may choose to forego further testing. But if you are 25 you will probably want to confirm the risks with additional testing such as ultrasound and amniocentesis.
The false positive rate for the alphafetoprotein triple screen is 1 in 140. This means that for every 140 positive results, one will be false. A positive result only means that further testing is advised, and your doctor will probably want to test the results with an ultrasound to confirm the age of the fetus and the presence of multiples. If the tests show that everything is normal, then your doctor will probably recommend amniocentesis to confirm the presence of Down's syndrome.
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