Karyotype: What It Is and What It Is Used For
What is a karyotype (in simple terms)
A karyotype is an organised “photograph” of your chromosomes. In humans we expect 46 chromosomes: 22 autosomal pairs plus one sex-chromosome pair (46,XX or 46,XY). When we look at them together, we are checking two things:
- Number — whether any chromosome is missing or extra (for example, a trisomy).
- Structure — whether any segments have been swapped, inverted or lost.
When we explain this during a consultation the same question usually comes up: “Does this karyotype thing have anything to do with why I’m not getting pregnant?” The short answer is sometimes — and we clarify below. But first, one key idea: a karyotype can come back “normal” and there may still be a genetic problem that this technique cannot see (because of its resolution limit). There are also “balanced” rearrangements (such as a balanced translocation): the person is healthy, but that structural change can make it harder to have children without pregnancy losses.
In practice, the laboratory cultures cells (usually blood lymphocytes), halts division at a specific stage and stains the chromosomes so they can be sorted. The final report summarises findings using standard notation (e.g. “46,XX” or a detailed structural change). This is where good clinical interpretation makes all the difference.
What a karyotype is used for in fertility and assisted reproduction
A karyotype is not a universal fertility test, but it does provide key information in specific situations. We use it to find out whether there are inheritable numerical or structural changes that explain recurrent pregnancy loss, implantation failure, unexplained infertility or certain semen analysis findings.
- Female infertility: an abnormal karyotype can increase the likelihood of chromosomally abnormal embryos and, therefore, of early losses.
- Male infertility: alongside other tests, a karyotype can uncover rearrangements that explain oligo/azoospermia and guide management.
- Assisted reproduction: the results can change the strategy: IVF (In Vitro Fertilization) / ICSI (intracytoplasmic sperm injection), considering PGT-SR (preimplantation genetic testing for structural rearrangements) or, in certain scenarios, egg or sperm donation.
During consultations we always stress two messages: “A ‘normal’ karyotype does not guarantee pregnancy; it simply rules out a specific set of problems. And a balanced finding does not always cause symptoms in the person, but it can increase the risk of losses.”
In short, its real value lies in identifying parental chromosomal causes that genuinely change decision-making in assisted reproduction. It does not replace other tests (hormones, semen analysis, uterine studies, etc.), but it complements the whole picture.
When is a karyotype requested: common criteria in the consultation
It is not about ordering it “just in case” but about requesting it when it changes management. Typical criteria:
- Recurrent pregnancy loss (≥ 2 clinically confirmed losses).
- Unexplained infertility, after a basic workup with no conclusive findings.
- Severe sperm abnormalities or a family history suggestive of rearrangements.
- Reproductive history with previous children affected by chromosomal anomalies.
- Before assisted reproduction when, given the history, the probability of a rearrangement is relevant.
Although there is no full consensus among scientific societies on when to perform it (except in the situations described above), many guidelines recommend including it in the basic infertility workup. At Love Fertility Clinic we ALWAYS request it before starting an IVF, egg donation or ROPA method (Reception of Oocytes from Partner) treatment.
One partner or both?
It depends on the context, but when there have been losses the usual approach is to test both partners. If the problem is found in only one, the plan is adapted accordingly (genetic counselling, PGT-SR, etc.). habitual es estudiar a los dos. Si el problema está en uno solo, el plan se adapta (asesoramiento genético, PGT-SR, etc.).
Quick checklist before assisted reproduction
- Have there been ≥ 2 losses or implantation failures?
- Has the basic workup found no clear cause?
- Is there a family or chromosomal history?
- Is the semen severely abnormal?
If you answer yes to any of these, a karyotype can help.
How it is done: sample, steps and timelines
Usual sample: peripheral blood. Other sample types exist (amniotic fluid, chorionic villi, bone marrow) for different contexts; in fertility and assisted reproduction we use blood in most cases.
What happens in the laboratory (short version):
- Blood draw and lymphocyte culture.
- Mitosis is halted and chromosomes are stained to reveal banding patterns.
- Photographing and sorting (karyogram).
- Reading and reporting by cytogeneticists.
Timelines: the process usually takes several weeks (depending on the laboratory and sample quality). It is best not to schedule critical clinical decisions until the report is available.
Risks: minimal (venipuncture).
Preparation: in general, no fasting or special precautions are needed.
What we tell our patients is: “The sample is just blood, the process takes time and the result is not instant. We prefer to explain this clearly so there are no unrealistic expectations.”
What a karyotype detects — and what it does NOT detect (and differences with PGT and microarrays)
A karyotype sees the large-scale map. That is a strength (it picks up “big” changes) and, at the same time, a limitation (it misses the small ones).
| What it detects well | What it does NOT detect (or detects poorly) |
|---|---|
| Aneuploidies (missing or extra chromosome) | Small variants: microdeletions/duplications below its resolution |
| Large rearrangements: translocations, inversions, large deletions/duplications | Point mutations in genes (e.g. cystic fibrosis, haemophilia) |
| Abnormal sex chromosomes (e.g. Turner syndrome, Klinefelter syndrome) | Low-level mosaicisms (may go undetected) |
| Inheritable patterns that explain losses | Non-chromosomal causes of infertility (endocrine, uterine, immunological, etc.) |
PGT (preimplantation genetic testing) vs. parental karyotype:
- The parental karyotype studies the couple.
- PGT-A (preimplantation genetic testing for aneuploidies) / PGT-SR studies embryos created through IVF. PGT-A screens for embryonic aneuploidies and PGT-SR is used when we know a parental rearrangement exists (e.g. a translocation). They are not the same and do not replace each other: they answer different questions.
Microarrays (CMA): they have higher resolution than a karyotype for small deletions/duplications, but they do not always detect balanced rearrangements. That is why, when a rearrangement is suspected, the karyotype remains essential.
Practical message: “If the parental karyotype is normal but problems persist, we can consider other techniques (PGT, microarrays or other genetic studies) depending on the case.”
Common results and what decisions follow
1) “Normal” karyotype (46,XX or 46,XY).
Good news: no large detectable chromosomal abnormalities. What next? We continue investigating other causes (ovarian, tubal, uterine, male factor, immunological) and adjust the assisted-reproduction strategy. An honest reminder: a normal karyotype does not rule out every genetic problem.
2) Balanced rearrangement (e.g. translocation).
The person is well, but the likelihood of non-viable embryos and losses increases. The usual recommendations are:
- Genetic counselling to understand the risks.
- Considering IVF with PGT-SR to select embryos that are balanced or normal.
- Evaluating donation in specific scenarios (depending on age, history and prognosis).
3) Aneuploidies or unbalanced rearrangements.
These require targeted investigation, specific reproductive options and, sometimes, psychological support because they change the plan.
4) Mosaicism.
This depends on the percentage and the chromosome involved. It usually requires confirmatory tests and individualised counselling.
In our experience, when a balanced translocation is found, what helps most is explaining the “why” behind the losses and presenting clear options: PGT-SR or donation, depending on age and context.
Practical decision-making in assisted reproduction (summary):
- Unbalanced → Specialist counselling; personalised reproductive options.
- Normal → Continue the overall workup; consider PGT-A depending on age and history.
- Balanced → IVF + PGT-SR; coordination with clinical genetics.
Frequently asked questions
A karyotype is a study of the number and structure of chromosomes. In fertility it helps identify inheritable abnormalities (aneuploidies or rearrangements) that explain pregnancy losses, implantation failure or unexplained infertility, guiding decisions such as IVF/ICSI and, where appropriate, PGT-SR or donation.
It is requested when the result changes the strategy: recurrent pregnancy loss (≥ 2), implantation failure, unexplained infertility, severe sperm abnormalities or a family history of rearrangements. At Love Fertility Clinic we perform it routinely for every couple before starting IVF or egg-donation treatment, because couples with fertility problems have a higher risk than the general population of carrying an abnormality (although the risk is still low) — and the finding would significantly change the prognosis.
When there have been losses or a rearrangement is suspected, the recommendation is to test both partners. This way we can pinpoint the origin and plan options such as PGT-SR if appropriate. In other contexts, the specialist decides who to test first based on the clinical history.
The laboratory cultures lymphocytes and analyses the chromosomes — a process that at Love Fertility Clinic typically takes 2–3 weeks. The exact timeframe depends on the centre and sample quality. It is best to plan clinical decisions once the final report is available.
It detects aneuploidies and large rearrangements (translocations, inversions, large deletions/duplications). It does not identify small microdeletions, point mutations or all low-level mosaicisms. In those cases, microarrays or other complementary genetic tests may be indicated.
The carrier is usually clinically healthy, but the risk of chromosomally abnormal embryos and pregnancy losses increases. Genetic counselling is usually recommended, along with considering IVF/ICSI with PGT-SR to select embryos with a normal or balanced karyotype.
The parental karyotype studies the couple and looks for inheritable risks; PGT analyses IVF embryos to select the most suitable ones. They complement each other: the first identifies the cause in the parents, the second optimises embryo selection.
There is no clear-cut recommendation from scientific societies to perform it in every case before IVF, but at Love Fertility Clinic we always do — for greater safety — since it is simply a blood test and the result could significantly change the prognosis and treatment plan.
No. A 46,XX or 46,XY result rules out large abnormalities but not microdeletions or point mutations. If infertility persists, the team may suggest microarrays, PGT-A or other tests depending on the clinical history and age.
The cost varies between public and private centres and depends on the clinical indication. In the public health system, coverage depends on the medical criteria and the autonomous community. In private care, the price and coverage depend on your insurance and the laboratory. Please check with your centre.
A karyotype is a simple test with high impact when there are recurrent losses, unexplained infertility or a family suspicion. It does not explain everything, but it does change decisions: from continuing with standard assisted reproduction to IVF / ICSI with PGT-SR or donation. The key is to request it when it is indicated, explain it clearly and combine it with the rest of the fertility workup.
