Aneuploidy Screening

Aneuploidy screening is testing used to estimate or evaluate whether an embryo, fetus, pregnancy, or sometimes sperm carries an abnormal number of chromosomes. In fertility care, prenatal care, and IVF, the term matters because chromosome number errors are a major cause of failed implantation, miscarriage, and certain genetic conditions. For men and couples trying to conceive, understanding aneuploidy screening can make test results, treatment decisions, and next steps much easier to navigate.

What is aneuploidy screening?
Key takeaways
Why aneuploidy screening matters
What aneuploidy screening means in men's health and fertility
How aneuploidy happens
Types of aneuploidy screening and related tests
What is normal vs abnormal?
How to interpret results
Aneuploidy screening in IVF and PGT-A
Aneuploidy screening during pregnancy
Does male fertility affect aneuploidy risk?
Treatment and management options
Common myths and misconceptions
Questions to ask your doctor
Related tests and terms
Frequently asked questions
References

What is aneuploidy screening?

Aneuploidy screening is a way to check for the possibility of missing or extra chromosomes. Humans usually have 46 chromosomes arranged in 23 pairs. If there is an extra chromosome or a missing one, that is called aneuploidy. Well-known examples include trisomy 21 (Down syndrome), trisomy 18, trisomy 13, and sex chromosome differences such as Turner syndrome or Klinefelter syndrome.

The word screening is important. A screening test does not give a final diagnosis. It estimates risk or identifies embryos or pregnancies that may be more likely to have a chromosome-number abnormality. Diagnostic tests, by contrast, are used to confirm whether the abnormality is truly present.

Depending on the setting, aneuploidy screening may refer to:

Prenatal screening during pregnancy, such as cell-free DNA screening, first-trimester screening, or second-trimester serum screening
Embryo testing in IVF, commonly called preimplantation genetic testing for aneuploidy, or PGT-A
Research or specialized sperm testing that evaluates chromosome abnormalities in sperm cells, usually in select infertility cases rather than routine care

Major professional groups including the American College of Obstetricians and Gynecologists and the American Society for Reproductive Medicine distinguish clearly between screening and diagnosis because false positives, false negatives, and uncertain results can occur.

Key takeaways

Aneuploidy means an abnormal number of chromosomes.
Aneuploidy screening estimates risk; it does not by itself confirm a diagnosis.
In pregnancy, screening may involve blood tests, ultrasound, or cell-free DNA testing.
In IVF, embryo aneuploidy screening is usually called PGT-A.
Maternal age is one of the strongest known risk factors for embryo aneuploidy.
Male factors may also contribute in some cases, especially severe sperm abnormalities or advanced paternal age, but the relationship is more complex.
Abnormal screening results often lead to follow-up diagnostic testing, counseling, or treatment planning.
The best test depends on whether the goal is prenatal screening, IVF embryo selection, or evaluation of recurrent pregnancy loss or infertility.

Why aneuploidy screening matters

Chromosome-number abnormalities are common in human reproduction. Many embryos created naturally or through IVF are aneuploid and never implant or result in early miscarriage. Screening can help explain why conception is taking longer, why IVF cycles may fail, or why a pregnancy screening result needs closer follow-up.

Why it matters depends on the clinical situation:

For couples trying to conceive naturally: prenatal aneuploidy screening can provide early information about risk in an ongoing pregnancy.
For IVF patients: embryo screening may help identify embryos more likely to be chromosomally normal, although it has limitations and does not guarantee success.
For men with infertility: aneuploidy-related discussions may come up if there is severe male factor infertility, recurrent pregnancy loss, repeated IVF failure, or abnormal sperm testing.

Chromosomal abnormalities are a leading cause of miscarriage, particularly in the first trimester. This is well established in reproductive medicine literature, including summaries available through NCBI Bookshelf.

What aneuploidy screening means in men's health and fertility

At first glance, aneuploidy screening may sound like a topic that applies only to embryos or pregnant women. In reality, it often becomes relevant in men's fertility care too.

From a male fertility perspective, the key question is whether sperm quality, sperm DNA integrity, age, testicular health, or genetic factors could raise the chance of creating embryos with chromosomal abnormalities. The answer is nuanced.

Where men fit into the picture

Sperm provide half the chromosomes in an embryo, so sperm chromosome abnormalities can matter.
Severe semen abnormalities such as very low sperm count, poor motility, or abnormal morphology may be associated with higher rates of sperm chromosomal errors in some men.
Advanced paternal age has been studied as a possible contributor to some chromosomal and genetic risks, though maternal age remains the dominant factor for most whole-chromosome aneuploidies.
Recurrent miscarriage or repeated IVF failure may prompt evaluation of both partners, including possible genetic testing.

Some studies suggest increased sperm aneuploidy rates in men with severe oligozoospermia or other male-factor infertility patterns, including data indexed on PubMed. Still, this does not mean every man with an abnormal semen analysis needs chromosome testing. Clinical context matters.

How aneuploidy happens

Aneuploidy usually results from an error in cell division. The process is called nondisjunction, meaning chromosomes do not separate properly when eggs, sperm, or early embryonic cells are formed.

Main mechanisms

Errors during egg formation during meiosis are a major source of embryo aneuploidy, which is one reason risk rises with maternal age.
Errors during sperm formation can also occur and may be more relevant in some infertility cases.
Errors after fertilization can create mosaic embryos, where some cells are chromosomally normal and others are abnormal.

Known or suspected contributors

Increasing maternal age
Some parental chromosomal rearrangements such as balanced translocations
Severe male factor infertility in select cases
Abnormal meiosis or mitosis
Embryo mosaicism

It is important not to overstate preventability. Most chromosome-number errors are not caused by anything a couple deliberately did or did not do. Lifestyle factors can affect fertility overall, but they are not a simple on-off switch for aneuploidy.

Types of aneuploidy screening and related tests

The term can refer to more than one test. The table below helps separate the most common options.

Comparison of common aneuploidy screening approaches

Table 1. Screening and diagnostic tests related to aneuploidy

Test or approach	When used	What it looks for	Screening or diagnostic?	Key limitation
Cell-free DNA (cfDNA/NIPT)	During pregnancy	Risk of common fetal chromosome abnormalities using maternal blood	Screening	High accuracy for some conditions but not definitive
First-trimester combined screening	Early pregnancy	Risk estimate using blood markers and nuchal translucency ultrasound	Screening	Less specific than cfDNA for some trisomies
Second-trimester serum screening	Pregnancy	Risk estimate for certain chromosome abnormalities and neural tube defects	Screening	Not diagnostic
Chorionic villus sampling (CVS)	Pregnancy	Direct fetal or placental genetic analysis	Diagnostic	Invasive procedure
Amniocentesis	Pregnancy	Direct fetal genetic analysis from amniotic fluid	Diagnostic	Invasive procedure
PGT-A	IVF embryos before transfer	Whether sampled embryo cells appear euploid or aneuploid	Screening	Embryo biopsy plus possible mosaic or inconclusive results
Sperm FISH or specialized sperm chromosome testing	Select male infertility cases	Chromosome abnormalities in sperm	Laboratory assessment, not routine screening for all men	Limited routine use and interpretation depends on context

Prenatal testing guidance from ACOG and embryo testing guidance from ASRM are useful starting points if you are comparing options.

What is sperm FISH?

FISH stands for fluorescence in situ hybridization. In reproductive medicine, sperm FISH can be used in selected cases to estimate the proportion of sperm carrying abnormal numbers of certain chromosomes. It is not a standard test for every man with infertility, but it may be considered when there is severe male factor infertility, recurrent pregnancy loss, repeated IVF failure, or concern about chromosomal risk.

What is normal vs abnormal?

In chromosome testing, the key term for normal chromosome number is euploid. The key term for abnormal chromosome number is aneuploid.

Quick definitions

Euploid: the expected number of chromosomes
Aneuploid: an extra or missing chromosome
Mosaic: a mixture of cells, some normal and some abnormal
Inconclusive or no-result: the test sample did not provide a clear answer

What is normal vs not normal in different settings?

Table 2. Interpreting common result language

Setting	Usually considered reassuring	Usually considered abnormal or concerning
Prenatal screening	Low-risk screen	High-risk or positive screen
Prenatal diagnostic testing	Normal karyotype or microarray result	Confirmed chromosome abnormality
IVF PGT-A	Euploid embryo result	Aneuploid embryo result
IVF PGT-A	Sometimes transferable depending on clinic policy if low-level mosaic and carefully counseled	High-level mosaic or non-transferable result depending on findings and clinic standards
Sperm chromosome testing	Results within lab reference expectations	Elevated sperm aneuploidy rates

There is no single universal “normal range” for aneuploidy screening the way there is for testosterone or sperm concentration. Interpretation depends on the exact test, the lab, the chromosomes evaluated, age, and the clinical setting.

How to interpret results

The most common mistake is assuming screening equals diagnosis. It does not.

If a prenatal screen is low risk

A low-risk result means the chance of the screened condition is lower, not zero. Screening tests can miss some abnormalities, and they usually do not assess every possible genetic or structural condition.

If a prenatal screen is high risk or positive

A positive screening result means follow-up is needed. The next step is often genetic counseling and a diagnostic test such as CVS or amniocentesis. ACOG specifically notes that cell-free DNA is the most sensitive screening test for common fetal aneuploidies, but it still has false-positive and false-negative results and is not equivalent to diagnostic testing: ACOG on cell-free DNA screening.

If an embryo is labeled euploid on PGT-A

This generally means the sampled cells did not show a chromosome-number abnormality for the tested chromosomes. It improves confidence in embryo selection, but it does not guarantee implantation, a healthy pregnancy, or live birth.

If an embryo is labeled aneuploid on PGT-A

This suggests the embryo has an abnormal chromosome count and is usually considered unsuitable for transfer. However, interpretation can be complex in cases involving mosaicism or technical limitations.

If results are mosaic or inconclusive

Mosaic findings can be difficult to interpret because the biopsied cells may not perfectly represent the whole embryo. Inconclusive results mean there was not enough quality information to confidently classify the sample. These findings often require detailed discussion with a fertility specialist and, when available, a genetic counselor.

Aneuploidy screening in IVF and PGT-A

In IVF, aneuploidy screening is usually called PGT-A, or preimplantation genetic testing for aneuploidy. A few cells are biopsied from the embryo, typically at the blastocyst stage, and analyzed to estimate whether the embryo is euploid, aneuploid, or mosaic.

Why PGT-A is used

To help prioritize embryos for transfer
To reduce transfer of embryos with clear chromosome-number abnormalities
To inform decision-making after recurrent implantation failure or miscarriage
To potentially shorten time to pregnancy in selected patients

Important limitations of PGT-A

It is a screening test, not a perfect diagnostic test
The biopsied cells come from the trophectoderm, not the inner cell mass that becomes the fetus
Mosaicism can complicate interpretation
Not every patient benefits equally
Embryo quality, uterine factors, age, and overall fertility health still matter

The role of PGT-A remains an active topic in reproductive medicine. Professional societies have emphasized that benefits may vary depending on patient characteristics and that counseling should be individualized. ASRM and ESHRE materials discuss both potential benefits and important caveats.

Aneuploidy screening during pregnancy

During pregnancy, aneuploidy screening is routine discussion in prenatal care. The goal is to estimate the chance that the fetus has certain chromosomal conditions.

Common prenatal screening options

Cell-free DNA screening (NIPT or cfDNA): uses fragments of placental DNA in maternal blood to screen for common trisomies and some sex chromosome conditions.
First-trimester screening: combines blood markers with ultrasound measurement of nuchal translucency.
Second-trimester serum screening: blood-based risk screening done later in pregnancy.

Common diagnostic follow-up tests

Chorionic villus sampling (CVS)
Amniocentesis

The NHS and ACOG both provide patient-friendly explanations of prenatal screening and diagnostic testing.

Does male fertility affect aneuploidy risk?

Sometimes. But the answer is not as simple as “poor sperm equals aneuploid embryo.”

What is known

Men with severe male factor infertility may have higher rates of sperm chromosomal abnormalities in some studies.
Certain testicular conditions, chromosomal disorders, or very abnormal semen parameters can raise concern for genetic issues.
Sperm DNA damage and sperm aneuploidy are related but not identical concepts.
Advanced paternal age may influence some reproductive and genetic risks, though it is not the main driver of common whole-chromosome aneuploidies.

What is less certain

Whether routine sperm aneuploidy testing improves outcomes for most infertile men
How much an abnormal sperm FISH result should change treatment in all scenarios
Whether lifestyle changes alone can meaningfully reduce established sperm aneuploidy rates in every case

If a man has severe oligospermia, azoospermia requiring surgical sperm retrieval, recurrent pregnancy loss with a partner, or repeated IVF failure, a reproductive urologist or fertility specialist may consider genetic workup. This can include karyotype testing, Y chromosome microdeletion testing in selected cases, or other specialized evaluations.

Treatment and management options

There is no pill that “treats” aneuploidy directly. Management depends on where the issue appears and what the test shows.

Possible next steps after abnormal or concerning results

Confirm the result when needed. For prenatal care, this may mean CVS or amniocentesis after a positive screen.
Meet with a genetic counselor. This can help you understand the condition, the reliability of the result, and your options.
Review fertility strategy. In IVF, this may involve transfer planning, another stimulation cycle, or discussion of mosaic embryos where appropriate.
Evaluate both partners. If there is recurrent miscarriage or severe infertility, broader genetic and fertility testing may be appropriate.
Address modifiable fertility factors. This may not eliminate aneuploidy risk, but improving overall reproductive health still matters.

Can you lower the risk naturally?

There is no proven lifestyle formula that prevents chromosome-number errors. Still, good preconception health is worth pursuing because it supports sperm production, hormone health, and pregnancy outcomes overall.

Avoid tobacco and recreational drugs
Limit excessive alcohol use
Address obesity and metabolic health when relevant
Manage heat exposure to testes when possible
Sleep adequately
Treat varicocele or hormonal issues when clinically indicated
Review medications and supplements with a clinician

These steps support reproductive health, but they should not be presented as guaranteed ways to prevent embryo or fetal aneuploidy.

Common myths and misconceptions

Myth 1: Aneuploidy screening gives a final yes-or-no diagnosis

False. Most forms of aneuploidy screening are risk estimates or screening classifications, not definitive diagnoses.

Myth 2: Aneuploidy is only a female factor issue

False. Maternal age is a major driver of embryo aneuploidy, but sperm can also contribute to chromosomal abnormalities in some cases.

Myth 3: A euploid embryo guarantees pregnancy

False. A euploid result improves confidence, but implantation, uterine factors, embryo biology, and chance still matter.

Myth 4: Poor semen analysis always means high aneuploidy

False. Some men with abnormal semen parameters do not have major sperm chromosome abnormalities, and some men with normal semen analyses may still have fertility challenges.

Myth 5: Lifestyle alone can fully prevent aneuploidy

False. Healthy habits support fertility but cannot completely control chromosome segregation errors.

Questions to ask your doctor

What exactly does my screening result mean: low risk, high risk, mosaic, or inconclusive?
Is this a screening test or a diagnostic test?
What follow-up testing do you recommend, and why?
If we are doing IVF, how reliable is PGT-A in our situation?
Do my semen analysis results suggest a need for genetic evaluation?
Should I see a reproductive urologist, fertility specialist, or genetic counselor?
How might age, miscarriage history, or prior IVF outcomes change your advice?
Would additional tests such as karyotype testing be useful?

Euploid: normal chromosome number
Aneuploid: abnormal chromosome number
PGT-A: preimplantation genetic testing for aneuploidy
PGT-M: testing embryos for a specific inherited genetic disorder
PGT-SR: testing for structural rearrangements
Karyotype: a chromosome analysis of cells
Mosaic embryo: embryo with a mix of normal and abnormal cells
Cell-free DNA screening: prenatal blood test that screens for common fetal chromosome abnormalities
CVS: chorionic villus sampling, a diagnostic prenatal test
Amniocentesis: diagnostic prenatal sampling of amniotic fluid
Sperm FISH: specialized sperm chromosome analysis in select cases

Frequently asked questions

Is aneuploidy screening the same as genetic testing?

Not exactly. It is one type of genetic screening focused on chromosome number. Some genetic tests look for single-gene disorders, structural chromosome changes, or other DNA variants instead.

Can a man be tested for aneuploidy?

In selected cases, yes. A man may have his own karyotype checked or undergo specialized sperm chromosome testing such as sperm FISH, but these are not routine tests for every fertility evaluation.

Does abnormal sperm morphology mean aneuploidy?

No. Abnormal morphology and aneuploidy are different findings. Some overlap may exist in severe infertility, but one does not automatically prove the other.

Is PGT-A worth it for IVF?

It depends on age, embryo number, prior IVF history, miscarriage history, and clinic practices. Some patients may benefit more than others. A personalized discussion with your fertility specialist is essential.

Can aneuploidy cause miscarriage?

Yes. Chromosomal abnormalities are a common cause of early pregnancy loss, especially first-trimester miscarriage.

What is the difference between a positive screen and a diagnosis?

A positive screen means increased risk. A diagnosis means the condition has been confirmed, usually with a diagnostic test such as CVS, amniocentesis, or definitive laboratory analysis.

Can a normal screening test miss a chromosome problem?

Yes. No screening test is perfect. A low-risk result lowers the likelihood of the condition screened for, but it does not reduce the risk to zero.

Does paternal age increase aneuploidy?

Paternal age may contribute to some reproductive and genetic risks, but maternal age remains the strongest factor for many common embryo aneuploidies. The exact effect of paternal age depends on the condition being discussed.

What happens after an inconclusive PGT-A result?

Your clinic may discuss re-biopsy in select situations, embryo storage, non-transfer, or other options depending on embryo quality and lab policy. The right path varies case by case.