Chromosome Analysis, Amniotic Fluid

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Test Details

Synonyms

  • Karyotype, Amniotic Fluid

Test Includes

15 to 20 mitotic spreads counted from separate in situ colonies; two banded karyotypes prepared

Use

The test determines fetal karyotype. The test allows prenatal detection of chromosomal rearrangements, aneuploidy, or mosaicism. Such groups include women who:

• are age 35 years of age or older

• have a previous child having chromosome abnormality or multiple congenital abnormalities

• have had two or more previous spontaneous abortions

• have a family history of a chromosome abnormality

• are known carriers of an X-linked disorder

• are 31 years of age or older with twin pregnancies

• have abnormal fetal ultrasound findings

• have a positive maternal serum marker screen

Additional biochemical or molecular tests may be performed on the cultured amniocytes.

Limitations

Although the overall culture success rate is reported as >99%, culture failure can result. Reasons include but are not limited to lack of amniocytes in the fluid, and contamination of the fluid with bacteria or yeast.

Methodology

In situ cell culturing of amniocytes to investigate numerical and/or structural chromosome abnormalities

Additional Information

Fetal loss rate at 14 to 18 week sampling is considered to be 0.5%, and 2% to 3% at 10 to 13 weeks.1 Chorionic villus sampling (CVS) may be safer than early amniocentesis for early prenatal diagnosis of cytogenetic abnormalities.2,3 The risk of miscarriage with CVS is 1% to 1.5% but the risk of maternal infection appears to be higher with CVS than with amniocentesis.4 Cytogenetic analyses using such samples allow for an early gestational testing based on a 10- to 11-week placental biopsy and a five-day cytogenetic study. Most failures are due to an inappropriate biopsy containing only maternal decidua. Chromosomal aberrations were found in 4.6% of fetuses in women older than 38 to 40 years of age. Trisomy 21 was the most common abnormality (62%). Klinefelter syndrome (11%) and Edwards syndrome, trisomy 18 (11%) were next most frequent in the cases of advanced maternal age.

Prenatal diagnosis is possible for more than 1000 inherited diseases. Most are inherited in an autosomal recessive manner. Antenatal diagnosis using gene probes has become available for cystic fibrosis, muscular dystrophy, sickle cell anemia, hemophilia, and many other genetic abnormalities. This can be done from either cultured amniotic fluid cells or chorionic villous sampling.5

Specimen Requirements

Specimen

Amniotic fluid, fetal urine, or cystic hygroma fluid

Volume

20 to 30 mL (15 to 20 mL for early amniocentesis)

Minimum Volume

5 mL (minimum volume may delay results due to fewer cells available for culture)

Container

Sterile plastic conical tube

Patient Preparation

The patient preferably should have had ultrasound studies (to verify fetal life, detect multiple gestation, confirm gestational age, localize fetus/placenta).

Collection

Discard first 2 mL of fluid aspirated to avoid maternal cell contamination. Specimen is collected in a 20 mL sterile syringe and transferred aseptically to sterile tubes to be transported to LabCorp. Request form is completed and accompanies specimen and miscellaneous slip to the laboratory.

Storage Instructions

Maintain specimen at room temperature. Do not freeze.

Causes for Rejection

Specimen found not to be amniotic fluid; gross contamination with blood cells; frozen specimen; container with rubber stopper (rubber is toxic to amniocytes)

Clinical Information

Footnotes

1. Nicolaides K, Brizot Mde L, Patel F, Snijders R. Comparison of chorionic villus sampling and amniocentesis for fetal karyotyping at 10-13 weeks' gestation. Lancet. 1994 Aug 13; 334(8920):435-439. Erratum: 1994 Sep 17; 344(8925):830. 7914564
2. Ledbetter DH, Zachary JM, Simpson JL, et al. Cytogenetic results from the US Collaborative Study on CVS. Prenat Diagn. 1992 May; 12(5):317-345. 1523201
3. Desnick RJ, Schuette JL, Golbus MS, et al. First-trimester biochemical and molecular diagnoses using chorionic villi: High accuracy in the US Collaborative Study. Prenat Diagn. 1992 May; 12(5):357-372. 1523203
4. DiLiberti JH, Greenstein MA, Rosengren SS. Prenatal diagnosis. Pediatr Rev. 1992 Sep; 13(9):334-342. 1409163
5. Chueh J, Golbus MS. Prenatal diagnosis using fetal cells in the maternal circulation. Semin Perinatol. 1990 Dec; 14(6):471-482. 2077667

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
052040 Chromosome, Amniotic Fluid 052138 Cells Counted 64095-3
052040 Chromosome, Amniotic Fluid 052139 Colonies 64096-1
052040 Chromosome, Amniotic Fluid 052140 Cells Analyzed 64092-0
052040 Chromosome, Amniotic Fluid 052141 Cells Karyotyped 64091-2
052040 Chromosome, Amniotic Fluid 052143 GTG Band Resolution Achieved 64093-8
052040 Chromosome, Amniotic Fluid 052144 Cytogenetic Diagnosis 33773-3
052040 Chromosome, Amniotic Fluid 052033 Cytogenetic Interpretation 64094-6
052040 Chromosome, Amniotic Fluid 052146 Specimen Type 31208-2
052040 Chromosome, Amniotic Fluid 052034 Director Review: 48672-0
052040 Chromosome, Amniotic Fluid 511936 PDF 80563-0

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