Chromosome Analysis – Amniotic Fluid
88235, 88267, 88280, 88291
Culture / Microscopy / Karyotype
Container: Two 15 ml sterile leak-proof conical tubes (discard 1st milliliter to avoid maternal cell contamination)
Optimal Quantity: 20-25 ml
Minimum Quantity: 10 ml
Storage: Room Temperature
Stability at Room Temperature: 8 hours, then refrigerate
Transportation: Avoid freezing or heating over 35OC
Final report in 7-10 days for 90% cases
A chromosome analysis on amniotic fluid may be clinically significant to identify genetic conditions associated with indications such as, advanced maternal age (AMA), sonographic anomalies, suspicious for trisomy 13, 18 or 21, abnormal quad screen, abnormal MaterniT21, open neural tube defect (NTD), genetic abnormality carrier and previous child with chromosome abnormality. It is also relevant in cases to confirm a chromosome diagnosis by FISH and MaterniT21.
Chromosome analysis on amniotic fluid is a procedure to rapidly culture and harvest amniocytes (amniotic cells) from amniocentesis for prenatal diagnosis of genetic and de novo (new or not genetic) chromosomal disorders. This type of analysis detects changes of the chromosome modal number, most often the common aneuploidies, and within the chromosome structure. Changes due to chromosome structure are usually associated with deletions or additions due to parent carrier status. Amniocytes are most viable when drawn by amniocentesis performed between 15 and 18 weeks gestation.
Amniotic fluid samples are long term cultures set up using the in situ method. If two tubes with fluid are received, two cultures are initiated, “A” and “B”. The cells are usually ready for harvest in about 7 days. Fifteen cells are counted and only one metaphase from each in situ colony is studied. Usually 8 cells from “A” culture is counted with 3 analyzed and 7 cells from “B” culture is counted with 2 analyzed, for a minimum of 5 completely analyzed metaphases. Abnormal cases may require analysis of additional cells which sometimes results in longer culturing time and turnaround time.
Interpretation of Results
The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report identifies the chromosomal sex and modal chromosome number. If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. Genetic counseling is recommended when chromosome aberrations, mosaic conditions, or unusual results are found, along with recommendation for further testing (i.e. microarray). References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information.
AFP / AChE
Alpha-fetoprotein (AFP) is a screening test to detect developmental abnormalities in the fetus. An AFP test is usually requested with the chromosome analysis. When the AFP is elevated, it is automatically reflexed for acetylcholinesterase testing.