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Prenatal Cytogenetics

Diagnosis of At-risk pregnancies

These are identified through one or several factors including:

  • Increased maternal age
  • Positive family history (e.g. previous affected child or one parent a known chromosome translocation carrier)
  • “High risk” maternal serum screening test result increasing mother’s risk of carrying fetus with chromosome abnormality
  • Anomalies seen on ultrasound scan indicative of chromosomal abnormality


Options for prenatal diagnosis

Having identified the at-risk pregnancy, parents will have various options including whether or not to undergo a prenatal diagnostic test, and choosing the most suitable type of prenatal diagnostic test for them. The type of test available is also dependent on the pregnancy’s gestation.


Chorionic villus sampling (CVS)

This procedure involves transabdominal needle sampling of the placenta, and is performed from the 10th week of gestation.
In general, results of the karyotype are available within approx. 14 days. In cases of scan anomalies and family history of chromosome rearrangements samples may be processed using a direct method which can give a preliminary result within 2-3 days. The risk of miscarriage after 1st trimester CVS is 2%.

Amniocentesis

This procedure involves transabdominal needle sampling of the amniotic fluid, and is performed from 15 weeks of gestation and onwards. In conjunction with the Molecular Genetics service, the Glasgow laboratory offers all it’s patients a rapid preliminary result for trisomy 13, 18 and 21 by Quantitative Fluorescence PCR (QF-PCR) within a few days of receipt, followed by a full karyotype result after 14-21 days. The risk of miscarriage after amniocentesis is 1%.