Why Get Tested?
To detect and diagnose some birth defects, genetic diseases, and chromosome abnormalities in a fetus, especially if pregnancy screening tests are abnormal; to evaluate fetal lung maturity; to help diagnose and monitor hemolytic disease in a fetus
When to Get Tested?
Between 15 and 20 weeks of gestation to test for genetic diseases, chromosome abnormalities, and open neural tube defects; when there is an increased risk of premature delivery, after 32 weeks to evaluate fetal lung maturity; when it is suspected that a fetus has hemolytic disease, about every 14 days
Sample Required?
A sample of amniotic fluid is obtained using a procedure called amniocentesis
How is it used?
Amniotic fluid analysis may used for several different reasons and the specific testing that is done depends on the reason for testing. The following list includes some of the more common ways that this analysis may be used:
Chromosome abnormalities or genetic disorders
Chromosome analysis, a cytogenetics test that may also be called karyotyping. Chromosome analysis will detect chromosome abnormalities associated with a variety of disorders. It evaluates the 22 paired chromosomes and the sex chromosomes (XY) in the nucleus of cells cultured from those collected in the sample of amniotic fluid and can be used to diagnose a variety of chromosomal disorders. Some of these include:
Down syndrome (Trisomy 21), caused by an extra chromosome 21 in all or most cells of the body
Edwards syndrome (Trisomy 18), associated with severe mental retardation; caused by an extra chromosome 18
Patau syndrome (Trisomy 13), caused by an extra chromosome 13
Klinefelter syndrome, the most common sex chromosome abnormality in males; caused by an extra X chromosome
Turner syndrome, caused by missing one X chromosome in females
As a byproduct, chromosome analysis can also definitely determine the sex of the fetus.
Genetic testing, also called molecular testing. It looks at fetal DNA to identify specific gene mutations and diagnose a variety of inherited diseases. Each test is ordered separately based upon the parents' personal and family histories. If a specific gene mutation is known to be present in the mother's or father's family, then that specific gene mutation can be tested for. While there are hundreds of genetic tests that can be performed, only a few are associated with relatively common disorders. Typically, only the most common mutations are tested; therefore, a fetus can still have an inherited disorder even though genetic testing did not identify one. A few examples of genetic tests more frequently performed include those for:
Cystic Fibrosis
Tay-Sachs disease
Canavan disease
Familial dysautonomia
Sickle cell anemia
Thalassemia
Birth defects
Testing for open neural tube defects (NTDs), such as spina bifida (spinal defect) or anencephaly (brain does not develop), detects chemicals that may be present in abnormal quantities when the fetus has an anatomic abnormality.
AFP (alpha-fetoprotein)—increased with neural tube defects
Acetylcholinesterase—increased with neural tube defects and also other anatomic abnormalities
Fetal Lung Maturity
Testing to evaluate fetal lung maturity may be performed if a woman is at an increased risk for premature delivery or an early birth is necessary for the baby or mother's health. The tests are based upon the presence of adequate protective liquid substances called surfactants in the lungs, which are necessary for proper lung function. If there are insufficient surfactants, a newborn may develop life-threatening neonatal respiratory distress syndrome (RDS). Tests include:
Fluorescence polarization (FPOL, surfactant/albumin ratio)
Lamellar body count
Phosphatidylglycerol (PG)
Lecithin/sphingomyelin (L/S) ratio (less common than FPOL)
Rh and other blood type incompatibilities and diseases
When a mother has been previously exposed through prior pregnancies or blood transfusions to red blood cell antigens that she does not have on her own red cells, she may develop antibodies against those red cell antigens (become sensitized). If the antigens are present on the red blood cells of the fetus (inherited from the father), then the fetus is at risk for a maternal-fetal incompatibility. The mother's antibodies can cross the placenta and bind to and destroy the fetus's red blood cells, causing hemolytic anemia. An affected fetus can be born with hemolytic disease of the newborn. One of the most commonly encountered incompatibilities is due to Rh, but there are many other blood types that may also cause this problem.
Tests for bilirubin may be performed on a regular basis, starting at about 25 weeks of pregnancy, to detect, evaluate and monitor the severity of the hemolytic anemia in the fetus.
Fetal Distress
Evaluation of amniotic fluid color – may be indicative of fetal distress
Green tinged – indicates that meconium, the fetus's first stool, has been released
Yellow to amber – may indicate bilirubin in the fluid
Red tinged – blood from the mother or the fetus
To detect and diagnose some birth defects, genetic diseases, and chromosome abnormalities in a fetus, especially if pregnancy screening tests are abnormal; to evaluate fetal lung maturity; to help diagnose and monitor hemolytic disease in a fetus
When to Get Tested?
Between 15 and 20 weeks of gestation to test for genetic diseases, chromosome abnormalities, and open neural tube defects; when there is an increased risk of premature delivery, after 32 weeks to evaluate fetal lung maturity; when it is suspected that a fetus has hemolytic disease, about every 14 days
Sample Required?
A sample of amniotic fluid is obtained using a procedure called amniocentesis
How is it used?
Amniotic fluid analysis may used for several different reasons and the specific testing that is done depends on the reason for testing. The following list includes some of the more common ways that this analysis may be used:
Chromosome abnormalities or genetic disorders
Chromosome analysis, a cytogenetics test that may also be called karyotyping. Chromosome analysis will detect chromosome abnormalities associated with a variety of disorders. It evaluates the 22 paired chromosomes and the sex chromosomes (XY) in the nucleus of cells cultured from those collected in the sample of amniotic fluid and can be used to diagnose a variety of chromosomal disorders. Some of these include:
Down syndrome (Trisomy 21), caused by an extra chromosome 21 in all or most cells of the body
Edwards syndrome (Trisomy 18), associated with severe mental retardation; caused by an extra chromosome 18
Patau syndrome (Trisomy 13), caused by an extra chromosome 13
Klinefelter syndrome, the most common sex chromosome abnormality in males; caused by an extra X chromosome
Turner syndrome, caused by missing one X chromosome in females
As a byproduct, chromosome analysis can also definitely determine the sex of the fetus.
Genetic testing, also called molecular testing. It looks at fetal DNA to identify specific gene mutations and diagnose a variety of inherited diseases. Each test is ordered separately based upon the parents' personal and family histories. If a specific gene mutation is known to be present in the mother's or father's family, then that specific gene mutation can be tested for. While there are hundreds of genetic tests that can be performed, only a few are associated with relatively common disorders. Typically, only the most common mutations are tested; therefore, a fetus can still have an inherited disorder even though genetic testing did not identify one. A few examples of genetic tests more frequently performed include those for:
Cystic Fibrosis
Tay-Sachs disease
Canavan disease
Familial dysautonomia
Sickle cell anemia
Thalassemia
Birth defects
Testing for open neural tube defects (NTDs), such as spina bifida (spinal defect) or anencephaly (brain does not develop), detects chemicals that may be present in abnormal quantities when the fetus has an anatomic abnormality.
AFP (alpha-fetoprotein)—increased with neural tube defects
Acetylcholinesterase—increased with neural tube defects and also other anatomic abnormalities
Fetal Lung Maturity
Testing to evaluate fetal lung maturity may be performed if a woman is at an increased risk for premature delivery or an early birth is necessary for the baby or mother's health. The tests are based upon the presence of adequate protective liquid substances called surfactants in the lungs, which are necessary for proper lung function. If there are insufficient surfactants, a newborn may develop life-threatening neonatal respiratory distress syndrome (RDS). Tests include:
Fluorescence polarization (FPOL, surfactant/albumin ratio)
Lamellar body count
Phosphatidylglycerol (PG)
Lecithin/sphingomyelin (L/S) ratio (less common than FPOL)
Rh and other blood type incompatibilities and diseases
When a mother has been previously exposed through prior pregnancies or blood transfusions to red blood cell antigens that she does not have on her own red cells, she may develop antibodies against those red cell antigens (become sensitized). If the antigens are present on the red blood cells of the fetus (inherited from the father), then the fetus is at risk for a maternal-fetal incompatibility. The mother's antibodies can cross the placenta and bind to and destroy the fetus's red blood cells, causing hemolytic anemia. An affected fetus can be born with hemolytic disease of the newborn. One of the most commonly encountered incompatibilities is due to Rh, but there are many other blood types that may also cause this problem.
Tests for bilirubin may be performed on a regular basis, starting at about 25 weeks of pregnancy, to detect, evaluate and monitor the severity of the hemolytic anemia in the fetus.
Fetal Distress
Evaluation of amniotic fluid color – may be indicative of fetal distress
Green tinged – indicates that meconium, the fetus's first stool, has been released
Yellow to amber – may indicate bilirubin in the fluid
Red tinged – blood from the mother or the fetus
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