A karyotype is a snapshot of an individual’s chromosomes. In order to generate a karyotype, the chromosomes are isolated, stained, and examined under the microscope. This is done to determine the number of chromosomes and is also used to highlight any abnormalities. A karyotype can identify genetic disorders, such as Down syndrome.

What is a karyotype?

A karyotype refers to an individual’s collection of chromosomes and genes. It’s also used as shorthand for a karyotype test, a laboratory technique that produces an image of an individual’s chromosomes. A karyotype test looks at the size, shape, and number of chromosomes.

In the fertility medicine world, karyotyping can be used to find out if an individual has a genetic disorder that could be passed down to children, or if a chromosomal defect is causing infertility issues or miscarriages. Doctors may also perform a karyotype on an embryo, in a process called preimplantation genetic testing, or in testing during pregnancy, to find genetic defects in a developing embryo or fetus.

Advanced maternal age, infertility, and a family history of genetic disorders are common reasons to order a karyotype test for parents or embryo(s).

Process of karyotype testing

A karyotype test requires a sample of cells. This sample can be retrieved through a simple blood test, or in a biopsy of a developing embryo. For prenatal testing, a doctor will insert a thin needle or catheter into the pregnant patient’s abdomen and withdraw a small amount of amniotic fluid or placental cells. This process is known as chorionic villus sampling or CVS. Bone marrow or tissue can also be collected via biopsy for a karyotype.

The cells are sent to a lab, where their genetic makeup is examined. If the cells contain the wrong number of chromosomes (the correct number is 46) or other genetic abnormalities, the karyotype results may be abnormal. Karyotyping can diagnose Down syndrome, Turner syndrome, intersex conditions, and other genetic conditions.

Karyotype and male fertility

There are potential genetic causes for male-factor infertility that can be diagnosed through karyotype testing. Klinefelter syndrome, for example, is a condition in which males have an extra X chromosome. This chromosomal abnormality interferes with puberty and fertility, though in vitro fertilization and intracytoplasmic sperm injection can help.