1. Clinical Indications being Essential.

Clinical indications are needed to determine test protocols and reporting time and interpret cytogenetic findings. Cytogenetic specimen will not be processed without clinical indications. If you need help for cytogenetic testing, please contact Cytogenetic Lab (519) 685-8500 x78974.

2. Parental Study for Multiple Miscarriages.

Recurrent chromosome abnormalities in miscarriages can occur if one parent is a carrier of a balanced chromosome rearrangement, such as a translocation or an inversion. When three or more miscarriages have occurred, both parents should be offered chromosome testing to detect a parental chromosome rearrangement. However, a history of a single or two spontaneous abortions is not indicative for chromosome study.

3. Chromosome Testing for Spontaneous Abortuses.

The finding of an abnormal karyotype in a spontaneous abortus does not provide predictive information regarding a subsequent pregnancy. While parental chromosome study is recommended for multiple miscarriages, Cytogenetic examination of products of conception for spontaneous abortuses is not necessary.

4. Chromosome Testing for Stillbirths.

Stillbirth is defined as fetal loss at a gestational age greater than 20 weeks or greater than 500 grams. Incidence of chromosome abnormalities is much higher among stillbirths than among live births. To meet the needs of Maternal-Fetal Medicine, the samples from stillbirths will be accepted for chromosome testing when unexplained gross congenital abnormalities have been observed by an obstetrician or a pathologist.

5. Verification of Results of Prenatal Diagnosis.

Experience from two large Canadian trials did not find any false positives for non-mosaic abnormal prenatal chromosomal results from amniocentesis samples (Lippman et al., 1992, Winsor et al., 1999). Therefore, cytogenetic confirmation of non-mosaic abnormal
chromosomal result is not a requirement. However, follow-up Cytogenetic confirmation should be attempted for situations, including a). prenatal finding of mosaicism; and b). discrepant phenotype/genotype outcome.

6. Family Study of Down Syndrome.

A family member with Trisomy 21, Down syndrome or suspected Down Syndrome is not considered as an indication for an unaffected individual to have chromosome testing. Cases are now usually referred to look for a translocation as an urgent study when a pregnancy has already occurred. If a translocational Down Syndrome was not confirmed in a family, such individuals do not have an increased risk of having offspring with Down Syndrome. If a translocation has been detected in an individual, chromosome study for other family members should be attempted as soon as possible to avoid unnecessary urgent management.

7. Amniotic Fluid and Chorionic Villus Sampling for DNA Testing of Mendelian Disorders.

When prenatal diagnosis is indicated for Molecular testing of Mendelian disorders, the Cytogenetics Laboratory will provide amniotic fluid culture and CVS cleaning for DNA testing only. Chromosome analysis will no longer be carried out as a routine process.

8. High Resolution Study.

High resolution G-banding analysis at =550-850 band levels may help detect certain microdeletion/microduplication syndromes and define the breakpoints of a rearrangement. However, a whole genome search from band to band without a specific target can be time consuming and often does not yield much useful information. A single gene disorder, such as Marfan Syndrome, a single physical sign such as an extra digit, or a single biochemical finding such as an elevated cholesterol level does not indicate a chromosome testing. A high resolution chromosome study will not help to make a diagnosis for such cases. A resolution higher than 700 bands (or prophase study) will be performed only for the cases when a particular chromosome deletion or duplication is suspected, or when such a study is requested by a Medical Geneticist.

Updated by Dr. Jie Xu 2009/11/23