Prenatal Amniotic Fluid Testing
Amniotic fluid is collected by amniocentesis performed during the second trimester, most often for chromosomal analysis, FISH analysis, or AFP quantitation with reflex testing to acetylcholinesterase and fetal hemoglobin. Please see below for further details.
|Test Description||Order Mnemonic||Test Number|
|Chromosome analysis with Alpha-Fetoprotein analysis & reflex testing||AFP/CHRM||1003950|
|Alpha-Fetoprotein analysis & reflex testing
(without chromosome analysis)
|AFP AM FL||3811175|
|Prenatal Screen, AneuVision(R) by FISH (13,18,21)||PRENATFISH||0112985|
PATIENT DEMOGRAPHIC INFORMATION & SPECIMEN REQUIREMENTS:
- Patient Diagnosis
- EDD (Estimated Date of Delivery)
- Gestational Age and method of determination: US or LMP
20-30 ml of amniotic fluid in well labeled sterile screw top tubes.
Avoid contaminating the fluid with blood (discard the first 2 cc collected; syringes not acceptable).
Gestational age (13-24 weeks) must be provided for interpretation of results.
Ship at room temperature. DO NOT FREEZE!
SPECIMEN VIABILITY DECREASES DURING TRANSIT. SEND SPECIMEN TO TESTING LAB FOR VIABILITY DETERMINATION; DO NOT REJECT!
Chromosome analysis is the microscopic examination of chromosomes in dividing cells allowing detection of changes in chromosomal number and structure. Deletions (eg, partial monosomy), duplications (eg, partial trisomy), and structural abnormalities such as translocations, inversions, and rings can also be detected. These chromosomal changes may be associated with infertility, miscarriage, stillbirth, birth defects, mental retardation, developmental delay, or abnormalities of sexual differentiation and development. Neoplasia may result from acquired tissue-specific cytogenetic aberrations in otherwise normal individuals.
The main reasons for performing chromosome analysis by amniocentesis are:
- Advanced maternal age.
- Previous offspring with chromosomal abnormality.
- Family history of chromosomal abnormality.
- Increased risk to the fetus based on the maternal serum prenatal screening tests.
- Fetal abnormality detected on ultrasonography.
Alpha-Fetoprotein analysis on amniotic fluid with reflexive testing is useful to diagnose neural tube and ventral wall defects. In the event of an elevated amniotic fluid AFP, acetylcholinesterase and fetal hemoglobin are automatically performed. There is an additional charge for the reflexive Acetylcholinesterase testing with Fetal Hemoglobin which is typically used to exclude the possibility fetal blood contamination.
Sensitivity of this conventional chromosome analysis method is best for larger chromosomal aberrations, and probe panels are limited to detect a few targeted abnormalities such as trisomy 13, trisomy 18 and trisomy 21. FISH analysis generally offers a faster turnaround time than conventional chromosomal analysis, but conventional chromosomal analysis is the more comprehensive and definitive test.