In plain words
A karyotype is a picture of a person's chromosomes. Cells are grown in a lab, paused in the middle of dividing, stained, and arranged in pairs by size. The result shows the number and shape of the chromosomes. It can find large changes, such as an extra copy of chromosome 21, which is linked to Down syndrome. It can miss smaller changes that other tests, such as , can find. In pregnancy, karyotypes often come from cells collected during or . Results often take one to two weeks. A karyotype answers a specific question about the chromosomes. It does not predict every health outcome for a child. A genetic counselor can explain what a result means for your family.
The deeper version
Conventional karyotyping uses G-banding of metaphase chromosomes from cultured cells, typically resolving structural changes of roughly 5 to 10 megabases. Prenatal samples are chorionic villi (CVS, 10 to 13 weeks) or amniocytes (amniocentesis, from about 15 weeks), and culture time sets the turnaround. Chromosomal microarray detects copy-number variants below karyotype resolution and, in prenatal diagnosis, adds yield for structural abnormalities with a normal karyotype (ACOG Practice Bulletin 226, 2020; ACMG practice guideline, 2013). Karyotyping remains useful for confirming mosaicism, balanced rearrangements, and cells of origin. The controversy is which test to offer first, and how to counsel about variants of uncertain significance found on microarray or exome sequencing.
Where it comes up
- Prenatal tests and ultrasounds: what each one isPregnancy: Your Body
- Pregnancy at 35 and olderPregnancy: Your Body
What mothers here say about karyotype
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Sources
- American College of Obstetricians and Gynecologists — Practice Bulletin No. 226: Screening for Fetal Chromosomal Abnormalities, 2020
- American College of Medical Genetics and Genomics — Chromosomal Microarray Analysis for Constitutional Cytogenetic Abnormalities, 2013