Karyotype analysis: why it's done and how to take it

A karyotype is a visual examination of the number and structure of all human chromosomes. In clinical practice, karyotype analysis typically refers to laboratory karyotyping, in which cells are grown, arrested in the division phase, stained, and examined under a microscope to see all chromosomes as an ordered set. [1]

Most people have 46 chromosomes in their cells, arranged in 23 pairs. Karyotyping assesses whether all chromosomes are missing, whether there is an extra chromosome, whether individual chromosomes are misshapen, and whether there are major rearrangements such as translocations, inversions, ring chromosomes, or marker chromosomes. [2]

From a clinical perspective, this test isn't "for all genetic diseases," but for major chromosomal changes. It's particularly useful when a physician suspects aneuploidy, a large deletion or duplication, a balanced rearrangement, mosaicism, or a tumor clone with a characteristic chromosomal rearrangement. It's in these scenarios that karyotyping remains relevant even with new technologies. [3]

Karyotyping is particularly well known for diagnosing Down syndrome, Turner syndrome, and Klinefelter syndrome, but its role is not limited to these. The analysis is also used for infertility, repeated pregnancy losses, some cases of primary amenorrhea, suspected chromosomal causes of congenital anomalies, and in oncohematology, where chromosomal rearrangements influence diagnosis, prognosis, and treatment options. [4]

It's also crucial to understand the limitations of the method. Karyotyping is a low-resolution study of the entire genome. According to the National Health Service Education Program in England, its typical resolution is approximately 5-10 megabases, so this test often misses small chromosomal losses and duplications, and especially point variants in genes. [5]

Table 1. What karyotyping typically detects and what it may miss

What does karyotyping typically reveal?	What karyotyping often doesn't reveal
An extra or missing chromosome	Small microdeletions and microduplications
Large deletions and duplications	Point changes in genes
Balanced translocations	Most monogenic diseases
Inversions	Uniparental disomy
Ring and marker chromosomes	Part of the mosaic states with a low proportion of abnormal cells
Some cases of mosaicism	Changes that are lost or do not grow in cell culture

Source for the table. [6]

When is analysis really necessary?

The most common understanding of karyotype analysis is related to pregnancy planning. And this is indeed one of the method's primary applications. Medical sources indicate that the test is used to assess chromosomal causes of infertility, recurrent miscarriages, stillbirths, and the risk of transmitting chromosomal abnormalities to the fetus. [7]

However, the modern approach to recurrent pregnancy loss has become more selective. In its updated 2022 guidelines, the European Society of Human Reproduction and Embryology does not recommend automatic parental karyotyping for all couples. It suggests doing so after an individual risk assessment, particularly if there are previous children with congenital anomalies in the family, if a translocation is detected in the pregnancy tissue, or if the family history itself is concerning. [8]

In male infertility, the role of karyotyping, on the other hand, remains very clear. Guidelines from the American Urological Association and the American Society for Reproductive Medicine recommend karyotyping and Y-chromosome microdeletion analysis for men with primary infertility, azoospermia, or severe oligozoospermia with elevated follicle-stimulating hormone levels, testicular atrophy, or suspected impaired sperm production. The same guidelines also recommend karyotyping evaluation for men with a history of recurrent pregnancy loss. [9]

Karyotype testing remains in demand in women, but not for mass screening. It is particularly appropriate in cases of primary amenorrhea, suspected Turner syndrome, gonadal dysgenesis, and certain types of premature ovarian failure. The American College of Obstetricians and Gynecologists noted that adolescents with primary amenorrhea have a high proportion of abnormal karyotypes, so this scenario requires genetic evaluation, not just hormonal testing. [10]

In pediatrics and clinical genetics, the role of karyotyping is no longer as universal as it once was. The American Academy of Pediatrics (AAP) in 2025 emphasizes that for delays in speech and language development and intellectual disabilities, the first genetic test is often chromosomal microarray analysis, sometimes in conjunction with exome sequencing. However, if a balanced rearrangement, a ring chromosome, or certain mosaic conditions is suspected, a karyotype is still necessary. [11]

In oncohematology, karyotyping remains crucial. It helps identify major rearrangements that shape a tumor clone and can determine disease classification, prognosis, and therapy. The US National Cancer Institute and the National Health Service in England specifically emphasize the importance of such rearrangements in leukemia and other blood diseases, including large translocations and gene fusions. [12]

Table 2. Main indications for karyotype analysis

Clinical situation	The role of karyotyping today
Infertility in a man with azoospermia or severe oligozoospermia	Often shown
Recurrent pregnancy loss	Not to everyone, but after risk assessment
Primary amenorrhea, suspected Turner syndrome	Often shown
Pregnancy with a high risk of fetal chromosomal abnormality	It is possible, but the choice of method depends on the situation.
A child with developmental delays and congenital anomalies	Often the first test will be a microarray rather than a karyotype.
Leukemia and other hematological tumors	Often important for diagnosis and prognosis
Suspected balanced translocation	Karyotyping is particularly useful

Source for the table. [13]

How the material is collected and how the research is conducted

Karyotyping cannot be performed on any biomaterial, but only on those containing nucleated cells suitable for culture. In practice, peripheral blood, skin cells, bone marrow, chorionic villi, amniotic fluid, and sometimes tissue from pregnancy loss are most commonly used. In oncohematology, blood and bone marrow are most important, while in reproductive medicine, parental blood and prenatal material are most important. [14]

During pregnancy, sample collection is performed either by chorionic villus sampling (CVS) or amniocentesis. According to MedlinePlus, CVS is typically performed between 10 and 13 weeks of pregnancy, while amniocentesis is performed between 15 and 20 weeks of pregnancy. The advantage of the former is an earlier pregnancy, while the advantage of the latter is the reduced impact of placental mosaicism on the outcome. [15]

The laboratory test itself involves several stages. Cells must be grown, stimulated to divide, arrested in metaphase, prepared, stained, and then the banding patterns on the chromosomes must be analyzed. This is why karyotyping is not an instant analysis and depends on the quality of the cell culture. [16]

The turnaround time also depends on the material. The National Health Service (NHS) Education Program for England indicates that blood and bone marrow cultures can take approximately 3 days, while skin and prenatal samples often require 7-14 days. The overall turnaround time, according to the same program, is typically 14-42 days, depending on the reason for the test and its urgency. [17]

Preparation for the test is usually minimal when it comes to blood karyotyping. For amniocentesis and chorionic villus sampling, preparation is determined by the obstetric team. The risks of routine blood sampling are minimal, and for invasive prenatal testing, MedlinePlus notes a small risk of cramping, discomfort, and pregnancy loss, so such procedures are only performed when indicated after genetic counseling. [18]

Table 3. What material is used to make a karyotype?

Material	When is it used most often?	Peculiarities
Peripheral blood	Infertility, amenorrhea, suspected constitutional chromosomal abnormality	The most common variant outside of pregnancy
Bone marrow	Leukemia, myelodysplastic syndromes and other blood diseases	Important for tumor cytogenetics
Chorionic villi	Early prenatal diagnosis	Usually 10-13 weeks of pregnancy
Amniotic fluid	Prenatal diagnostics in the second trimester	Usually 15-20 weeks of pregnancy
Leather	For some mosaic conditions and special tasks	Cell culture is needed
Tissue after pregnancy loss	Search for the chromosomal cause of loss	Interpretation depends on the quality of the material

Source for the table. [19]

How to read the result

The karyotyping result usually looks like a short formula, but it contains a wealth of information. A normal female karyotype is written as 46,XX, a normal male karyotype as 46,XY. The presence of an extra chromosome 21 in Down syndrome is written as 47,XX,+21 or 47,XY,+21, the absence of one X chromosome in Turner syndrome is written as 45,X, and an extra X chromosome in a man with Klinefelter syndrome is written as 47,XXY. [20]

A normal result means that 46 chromosomes were detected in the cells examined, with no noticeable structural changes. However, clinically, this does not automatically rule out a genetic disorder. A normal karyotype does not exclude minor copy number changes, monogenic diseases, epigenetic abnormalities, some mosaicism, and variants not present in the examined tissue or lost during cell culture. [21]

An abnormal result can be numerical or structural. Numerical changes include trisomies and monosomies, while structural changes include translocations, inversions, ring chromosomes, large deletions, and duplications. Some of these changes are balanced, meaning the carrier does not lose or gain visible chromosomal material, but the risk to offspring may be increased. This is why an apparently healthy adult may be a carrier of a rearrangement that affects fertility or pregnancy outcomes. [22]

A particular complication is mosaicism. Karyotyping can detect mosaic cell lineages, which is one of its advantages, but sensitivity depends on the proportion of abnormal cells, the tissue, and the culture characteristics. The National Health Service in England notes that some variants may not be detected in culture because abnormal cells are less well preserved or are lost during growth. [23]

In prenatal diagnosis, interpretation requires even greater caution. Chorionic villus sampling analyzes placental tissue, and the placenta does not always fully reflect the fetal chromosomal makeup. The US Centers for Disease Control and Prevention (CDC) states that mosaic trisomy detected in chorionic villus sampling requires confirmation with a postnatal sample because mosaicism may be confined to the placenta. [24]

Table 4. Examples of typical karyotype records

Recording	What does it mean?
46,XX	Normal female karyotype
46,XY	Normal male karyotype
47,XX,+21	Female karyotype with trisomy 21
45,X	Karyotype compatible with Turner syndrome
47,XXY	Karyotype compatible with Klinefelter syndrome
46,XX,t(14;21)	Balanced translocation between chromosomes 14 and 21
mos 45,X[10] 46,XX[20]	Mosaicism with 2 cell lines

Source for the table. [25]

How does karyotyping differ from microarray analysis, sequencing, and other tests?

Modern genetic diagnostics has long ceased to be limited to a single test. In some situations, a karyotype is needed, in others, a chromosomal microarray analysis, and in still others, exome or genome sequencing. The right choice is determined not by the latest technology trends, but by the specific changes the doctor is looking for. [26]

The main advantage of karyotyping over chromosomal microarray analysis is that it reveals the position of chromosomal material and can detect balanced translocations and inversions. Microarray analysis looks primarily at the quantity of chromosomal material, not its location, and therefore typically fails to identify carriers of balanced rearrangements. For this reason, karyotyping remains particularly valuable in cases of infertility and recurrent pregnancy loss. [27]

The advantage of chromosomal microarray analysis over karyotyping is its much higher resolution. The National Health Service in England states that microarray analysis detects copy number variants in the range of approximately 50-200 kilobases, whereas a karyotype is typically limited to changes of 5 megabases or more. Therefore, in cases of developmental delay, intellectual disabilities, autism, epilepsy, and multiple congenital anomalies, microarray analysis is often the first test. [28]

In prenatal medicine, the distinction is also fundamental. The American College of Obstetricians and Gynecologists recommends prenatal chromosomal microarray analysis if the fetus has one or more major structural abnormalities based on ultrasound examination. The same college's guidelines note that in stillbirths, microarray analysis provides a higher diagnostic yield than karyotyping, particularly for dysmorphisms, growth disorders, anomalies, and hydrops fetalis. [29]

Exome or genome sequencing addresses a different challenge: identifying changes at the gene level. In 2025, the American Academy of Pediatrics noted that exome sequencing, along with chromosomal microarray analysis, has become a first-line diagnostic tool for developmental delays and intellectual disabilities. However, sequencing has its own limitations: it does not replace karyotyping where balanced chromosomal rearrangements are needed. [30]

Targeted cytogenetic methods occupy an intermediate position. They do not replace a complete karyotype, but they allow for rapid confirmation or clarification of a specific rearrangement, assessment of the location of a duplication, or verification of a suspected tumor rearrangement. In oncohematology, such methods are often used in conjunction with karyotyping and molecular tests, rather than instead of them. [31]

Table 5. Karyotyping and other genetic methods

Method	What does he see best?	Main advantages	Main limitations
Karyotyping	Chromosome number, major rearrangements, balanced translocations, part of mosaicism	Sees the position of chromosomal material	Low resolution, cell culture required
Chromosomal microarray analysis	Small deletions and duplications throughout the genome	High resolution	Usually does not see balanced translocations and inversions
Exome or genomic sequencing	Changes in genes	High value in monogenic diseases	Does not replace karyotype in case of balanced rearrangements
Targeted cytogenetic test	Specific chromosomal regions and rearrangements	Rapid refinement of the target finding	It is not a complete overview of the entire genome.

Source for the table. [32]

Limitations, risks, and what to do after the results

The first and most important limitation of the method is its low resolution. Karyotyping works well for large chromosomal changes, but is significantly inferior to microarray analysis in detecting small deletions and duplications. Therefore, when prescribing a karyotype, a physician should always be certain that this class of abnormalities is the most likely. [33]

The second problem is the need for dividing cells and cell culture. This slows down the test and creates a risk of culture artifacts—changes that occur not in the patient's body but during cell growth in the laboratory. The National Health Service in England also notes that some true variants may, conversely, be lost in the culture and not be included in the final result. [34]

The third boundary is that a negative result cannot be interpreted as a complete prohibition on further diagnostics. If the clinical picture convincingly points to a genetic cause, but the karyotype is normal, the next step is often chromosomal microarray analysis, followed by sequencing. This is especially relevant in children with developmental delays, congenital anomalies, and abnormal neurodevelopment. [35]

After receiving a pathological result, genetic counseling is almost always required. This is necessary not only for interpreting the transcript, but also for prognosis, assessing the risk of recurrence in the family, choosing prenatal strategies for future pregnancies, and deciding whether to test parents, siblings, or children. This is especially important for balanced translocations, mosaicism, and incidental sex chromosome rearrangements. [36]

In prenatal diagnosis, following a positive screening, one more rule must be kept in mind: screening does not equal diagnosis. The American College of Obstetricians and Gynecologists emphasizes that if a cell-free prenatal screening result is positive, confirmation should be achieved by a diagnostic test, such as chorionic villus sampling or amniocentesis. Once the diagnostic material is obtained, a decision is made whether a karyotype, microarray analysis, or both are needed. [37]

Table 6. Main advantages and limitations of karyotyping

Advantages	Restrictions
Sees balanced translocations and inversions	Low resolution compared to microarray analysis
Gives a picture of all chromosomes at once	Doesn't see most minor copy changes
May detect some mosaic states	Requires dividing cells and cultivation
Useful for infertility and oncohematology	Slower than many modern methods
Provides structural and positional information	A normal result does not rule out a genetic disease.

Source for the table. [38]

Frequently Asked Questions

What is a karyotype analysis in simple terms?
It's a test in which a doctor and laboratory evaluate the number and structure of chromosomes. This method helps identify major chromosomal changes that may cause congenital syndromes, infertility, recurrent pregnancy loss, or certain blood disorders. [39]

Are karyotyping and chromosomal microarray analysis the same thing?
No. Karyotyping is better at detecting large rearrangements and balanced translocations. Chromosomal microarray analysis is significantly more sensitive to small deletions and duplications, but usually does not detect balanced rearrangements. [40]

When is a karyotype particularly useful?
Primarily, when a balanced translocation is suspected, in men with severe spermatogenesis disorders, in some cases of primary amenorrhea, in prenatal diagnosis for certain indications, and in oncohematology, where chromosomal rearrangements influence diagnosis and treatment. [41]

Do all couples need a karyotype after two miscarriages?
Today, the approach has become more individualized. European guidelines do not recommend automatically assigning a parental karyotype to all couples, but suggest assessing family history and other risk factors. However, some American reproductive guidelines maintain a broader role for karyotyping in men in couples with recurrent pregnancy losses. [42]

Can a normal karyotype rule out all genetic diseases?
No. A normal karyotype does not exclude small microdeletions, microduplications, point changes in genes, and other genetic mechanisms of disease. When clinical suspicion is high, additional testing is often needed. [43]

Which is better for a child with developmental delay: karyotype or microarray analysis?
In many cases, the first test today is chromosomal microarray analysis, sometimes combined with exome sequencing. However, if the doctor suspects a balanced rearrangement or part of a mosaic condition, karyotyping remains valuable. [44]

At what stage of pregnancy is a fetal karyotype performed?
If the sample is obtained through chorionic villus sampling, the test is usually possible between 10 and 13 weeks. If through amniocentesis, it is more often performed between 15 and 20 weeks. However, in real-life practice, the decision is not only about the gestational age but also about which genetic analysis method will be most informative in a given situation. [45]

Are chorionic villus sampling and amniocentesis dangerous?
Both procedures are considered generally safe, but they are not completely risk-free. MedlinePlus notes a small risk of pain, cramping, and pregnancy loss, so these tests are only prescribed after a careful discussion of the benefits and risks. [46]

How long does it take to get results?
This depends on the material and the laboratory. Blood and bone marrow cell cultures are usually faster, while skin and prenatal samples take longer. Overall, results often take between 14 and 42 days, although local timeframes may vary. [47]

Is a karyotype necessary for leukemia?
Very often, yes. In oncohematology, chromosomal rearrangements help clarify the diagnosis, tumor biology, prognosis, and sometimes treatment choices. This is why karyotyping remains an important test for a number of leukemias and other bone marrow diseases. [48]

Conclusion

Karyotype analysis is not an outdated method, but it is not universal. Its main strength today lies in the detection of major chromosomal abnormalities, especially balanced rearrangements, some mosaic states, and tumor cytogenetic anomalies. It still holds an important place in reproductive medicine and oncohematology. [49]

At the same time, modern practice requires a clear understanding of when a karyotype alone is insufficient. In cases of developmental delays, multiple congenital anomalies, and certain prenatal scenarios, chromosomal microarray analysis is more informative, while sequencing is more effective when a monogenic disorder is suspected. Therefore, the best approach today is not to "take any genetic test," but to choose a method tailored to a specific clinical need. [50]