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•  Description of methods used to obtain cells for karyotype analysis – e.g. chorionic villi sampling 

   and amniocentesis and the associated risks

Karyotyping is the process by which chromosomes are organised and visualised for inspection

  • Karyotyping is typically used to determine the gender of an unborn child and test for chromosomal abnormalities

Cells are harvested from the foetus before being chemically induced to undertake cell division (so chromosomes are visible)

  • The stage during which mitosis is arrested will determine whether chromosomes appear with sister chromatids

Finally, chromosomes are stained and photographed, before being organised according to structure

  • The visual profile generated is called a karyogram

Chorionic Villi Sampling

Chorionic villi sampling involves removing a sample of the chorionic villus (placental tissue) via a tube inserted through the cervix

  • It can be done at ~11 weeks of pregnancy with a slight risk of inducing miscarriage (~1%)


Amniocentesis involves the extraction of a small amount of amniotic fluid (contains fetal cells) with a needle

  • It is usually conducted later than CVS (~16 weeks of pregnancy) with a slightly lower risk of miscarriage (~0.5%)

Amniocentesis vs Chorionic Villi Sampling (CVS)

amniocentesis vs cvs