Amniotic Fluid Chromosome Analysis
The Cytogenetics Laboratory at Cincinnati Children's Hospital Medical Center brings a team of experts to provide highest-quality prenatal chromosome analysis on amniotic fluid samples. Doctors do not need to be affiliated with Cincinnati Children’s Hospital to order testing.
Download a Test Requisition Form
You can download the Prenatal Test Requisition form in portable document format (.pdf).
About the Testing | Indications | Specimen l Methodology l Sensitivity l Turnaround Time l Cost l CPT Codes l Shipping l Results l Contact Us
Amniotic fluid is fluid from the amniotic sac surrounding a fetus. Amniotic fluid (AF) serves as a cushion to protect the growing baby, but also a source of oxygen, proteins, and other substances that the baby needs for growth. Amniotic fluid contains proteins and fetal cells that can provide information about the genetic makeup of the fetus. A sample of this fluid for testing is obtained by amniocentesis, usually between 16-18 weeks gestation, but that time may vary. Fetal cells from the amniotic fluid can then be used for chromosome, alpha-fetoprotein (AFP), or other genetic or metabolic analysis.
Amniotic fluid chromosome analysis is a process by which a fetus’ cells are tested for any major changes in their chromosome structure or number. Chromosomes are the packages of genetic material. Most of us have 46 chromosomes that come in 23 pairs. When chromosome analysis is done, we are looking to see if there are extra or missing pieces of chromosomes that could affect the fetus’ development. To accomplish this, the laboratory first cultures or grows cells from a fetus that are found in the amniotic fluid. The procedure then involves stopping the cells during division to capture the chromosomes in their most condensed form. These condensed forms of chromosomes are necessary for performing the analysis. After the cells are applied to microscope slides, they undergo staining, which makes the condensed chromosomes appear with dark and light bands to allow for a technician to tell if regions are missing, gained, or rearranged in some way. Expertly-trained and experienced technicians in the Cytogenetics Laboratory at Cincinnati Children’s Hospital Medical Center use state-of-the-art computer imaging software and a trained eye to compile a picture (or karyogram) of the chromosomes 1-22, plus the sex chromosomes X and Y, which allows visualization of large (on an amniotic fluid sample this could be as small as several megabases) chromosome deletions, duplications, rearrangements (such as translocations when parts of two chromosomes are exchanged or traded), or extra or missing chromosomes (trisomy 21, marker chromosomes, ring chromosomes, etc.) Results are then reviewed by a Ph.D. or M.D. cytogeneticist and then reported to the patient’s physician.
About AFP Testing
Alpha-fetoprotein (AFP) is a normal protein produced by a fetus, and can be detected in the amniotic fluid. The typical amount of amniotic fluid AFP starts decreasing around the second trimester of pregnancy. In pregnancies where the fetus has a severe Rh incompatibility, lung immaturity, open body wall defect, or a neural tube defect such as spina bifida, the amount of AFP in amniotic fluid will be abnormal; hence, AFP can be used for fairly accurate detection of certain problems.
Which patients should be offered amniotic fluid chromosome analysis?
Women whose fetuses are at increased risk of chromosome imbalance (extra or missing genetic material) due to:
- advanced maternal age (over age 35 years at time of delivery)
- Prenatal screening by showing increased risk for chromosome abnormalities
- Abnormalities on ultrasound which may indicate chromosome abnormality
- Testing for a known familial chromosome or other genetic abnormality
| Amount Needed |
20 ml
3-5 ml additional fluid needed if ordering FISH probe study |
| Quality |
Clear |
| Collection / Transport Container |
Sterile centrifuge tubes (provided by lab) placed in a sealed plastic biohazard transport bag. The container and tubes must be leak-proof. |
| Specimen Labeling |
All specimen containers: Patient full name; date of birth; gestational age; diagnosis. |
| Storage Conditions |
Room temperature, protect from light. The specimen must be delivered immediately to the lab. |
| Transport Temperature |
Room temperature |
| Other |
The first few mls of fluid which are routinely discarded may be sent in a separate, clearly marked tube, and will be used for AFP and /or AchE determination. |
The sample must be sent out for immediate delivery to the laboratory. Please call 513-636-4474 for sterile centrifuge tubes or free local courier pickup service.
Amniotic fluid cells are cultured, then mitotic cells within the AF arrested with colcemid. Cells are fixed and the chromosomes spread by dropping the cells onto a microscope slide, or in the case of coverslips, by drying with forced air. Chromosome analysis is performed on at least two independent cultures, 15 different colonies in each. One cell from each colony is counted for modal number, sex chromosomes, and common trisomies. In a minimum of five of these cells, chromosomes are each counted band-for-band to detect any additional/deleted material.
We will reflex to AFP testing if the sample is from 13-22 weeks gestation.
We can also perform cell culture only on the amniotic fluid sample, without chromosome analysis, for use in other types of genetic testing or for indefinite frozen storage.
What can be detected by this test?
Amniotic fluid chromosome analysis can test for extra or missing chromosome material (for example, Down syndrome caused by 3 copies of chromosome 21), large (on an amniotic fluid sample this could be as small as several megabases) chromosome deletions, duplications, rearrangements (such as translocations of chromosome pieces from one chromosome body to another), and other known genetic conditions. Some abnormalities detected by amniotic fluid chromosome analysis are not able to be well-characterized without additional testing.
Limitations of this test include:
- Subtle chromosome abnormalities may not be detected by amniotic fluid chromosome analysis.
- Some abnormalities detected by amniotic fluid chromosome analysis are not able to be well-characterized without additional testing.
- Maternal contamination: If the amniotic fluid sample contains cells from the mother’s body (we may be alerted to this possibility if the sample appears bloody), the result could reflect the mother’s chromosomes rather than, or in addition to, the fetus’. This is a rare occurrence and we reduce the chances of inaccurate results by studying the appearance of the cells using a microscope to assure they appear to be of fetal origin.
- Mosaicism: Some fetuses have more than one type of chromosome makeup in their bodies. For example, the blood may have a different chromosome makeup than the skin cells, or the blood itself may contain 2 different “lines” of cells with different chromosome makeup. Amniotic fluid chromosome analysis has the limitation of not always characterizing mosaicism accurately. If a fetus has mosaicism, it might not be detected in the cells which happen to be studied by amniotic fluid chromosome analysis. Alternatively, amniotic fluid chromosome analysis may show a mosaic result when the fetus really doesn’t have mosaicism (ie, a false positive), if there is a twin’s cells present in the AF sample or if maternal cells have contaminated the sample (see above). These are rare occurrences.
- There are many genetic disorders that are caused by small changes in a person’s DNA which cannot be detected by this test.
- A normal result on amniotic fluid chromosome analysis does not mean that a child will not be born with birth defects, or cannot develop other problems later in life, such as developmental disabilities, diabetes, hypertension, attention deficit disorder, etc.
Amniotic Fluid Chromosome Analysis: 7-8 days
Amniotic Fluid Cell Culture Only: 7-8 days
Estimated TAT is based on receiving an optimal amount of sample in good condition. If suboptimal sample is received TAT may be longer than stated.
Please call our toll-free billing hotline at 1-866-450-4198 for current pricing, billing inquiries or for assistance with insurance preauthorization.
Amniotic Fluid Chromosome Analysis (Reflex to AFP if 13-22 wks gestation) 88235(2), 88269, 88280, 88285
Amniotic Fluid Cell Culture Only: 88235(2)
AFP (Reflex to AchE if AFP is elevated): 82106
AchE 82013
- Please enclose test requisition with sample. All information must be completed before sample can be processed.
- Place samples in Styrofoam mailer and ship at room temperature by overnight Federal Express to arrive Monday through Friday.
- Samples are delivered by couriers between 10:00AM – 12:00 midnight.
- After-hours and weekend samples should be delivered to Children's Hospital Laboratory Processing, Location B, 4th floor.
- It is the policy of the laboratory to accept and set up all specimens regardless of sample size or condition. If the specimen is judged to be less than optimum, the physician will be notified immediately by phone or FAX that the turnaround time may be increased.
Ship to:
Cytogenetics and Molecular Genetics Laboratories
3333 Burnet Avenue NRB 1005
Cincinnati, OH 45229
513-636-4474
Each test report includes a detailed interpretation of the genetic findings, any known clinical significance of the result, and recommendations for additional testing, if warranted. Results will be reported to the referring physician or health care provider as specified on the test requisition form.
AFP and AchE - These results will be included as an addendum to the original amniocentesis report, once received from the outside laboratory that performs this testing.
For additional inquiries, contact us:
Phone 513-636-4474
Fax 513-636-4373
Email cytogenetics@cchmc.org
