CYTOGENETICS DEPARTMENT

Prenatal Cytogenetics

Prenatal detection of cytogenetic abnormalities either by amniocentesis (approx. 300 samples per annum) or by chorionic villus sampling (approx. 30 samples per annum). Samples are received from Obstetrics clinics in Ninewells and at Perth Royal Infirmary.

Amniocentesis:

Approximately 300 amniocentesis samples per annum are carried out in Tayside for fetal karyotyping each year. The test is routinely performed at about 16 weeks gestation, mostly as a consequence of maternal serum screening for Down syndrome. A sample of amniotic fluid (about 15ml) is drawn off trans-abdominally under ultrasound guidance. Cells from the fluid are cultured and karyotyped. As well as detecting Down syndrome, this technique may also be used for prenatal diagnosis in families carrying known chromosomal rearrangements, or in pregnancies with abnormal ultrasound.

Results are routinely available in 12-14 days.

Additionally, a QF-PCR rapid aneuploidy screening is carried out on all amniotic fluid samples, to detect trisomies responsible for Down, Edward and Patau syndromes. Preliminary results are routinely available within 24-72 hours of the procedure, but are always backed up by full karyotyping, as not all chromosome anomalies are detected.

Chorionic Villus Sampling (CVS):

We process between 20 and 30 CVS samples per annum. A small sample of placenta is taken, transabdominally, under ultrasound guidance. CVS can be taken earlier in pregnancy. A preliminary "direct" result is usually available the following day. However, this result may be slightly less reliable than amniocentesis, due to confined placental mosaicism, and patients should be counselled accordingly. Confirmation from long term culture takes up to 14 days.

CVS sampling is particularly useful in cases where abnormality is detected on scan, but the pregnancy is not far enough advanced for amniocentesis sampling, or in cases where there is a previously known family history of a chromosomal or other genetic condition

Solid Tissue Samples:

Solid tissues are referred for: recurrent pregnancy loss (3 or more), fetal abnormality detected prenatally or at post mortem, mosaicism studies, cell culture for molecular genetic or biochemical studies

Results are usually available within 28 days.

Sample requirements:

Fresh samples only should be sent, formalin fixed specimens are unsuitable. Sterile tissue transport medium is available from the laboratory on request (x 33107). Consult User Manual or phone the department for more details on sample suitability.

For specific queries about the prenatal cytogenetics service, contact Miss.C.Maliszewska at the department on 01382-496735. E-mail: cmaliszewska@nhs.net. Patient queries should be directed to Specialist Midwives Lesley Mays, and Amanda Sullivan at Ninewells Hospital, and to the individual consultants at Perth and elsewhere.