Aneuploidy means an embryo carries an irregular number of chromosomes, a genetic alteration that can interrupt the course of a pregnancy. Here we explain its causes and how to reduce the risk.

What is aneuploidy and why does it matter?

Human body cells usually carry 23 pairs of chromosomes (46 in total), while eggs and sperm carry only 23 single chromosomes. When a cell has the correct number, we call it euploidy. Aneuploidy happens when a chromosome is missing or there is one too many. A missing chromosome is called a monosomy, and an extra one a trisomy.

Most monosomies (with the exception of monosomy X, or Turner syndrome) are not compatible with life. Trisomies can cause serious problems, such as trisomy 21, known as Down syndrome (1 in every 700 births), which involves congenital heart conditions, variable intellectual disability, and an average life expectancy close to 50 years.

How does aneuploidy arise in the reproductive process?

Most aneuploidies appear during gametogenesis (especially in meiosis I of oogenesis) or in the first divisions after fertilization. In assisted reproduction, close to 50% of embryos show aneuploidies. That percentage rises as maternal age advances, particularly after 37.

The most frequent trisomies in IVF affect chromosomes 16, 19, and 21. Among monosomies, the most common involve chromosome 22 and partial losses of the Y chromosome.

To go deeper into causes and prevention, visit What are aneuploidies: causes and how to prevent them?

Tests to detect and prevent aneuploidy in embryos

Preimplantation Genetic Testing (PGT) evaluates the chromosomes of embryos created through IVF. Using it raises the chances of achieving a pregnancy and a healthy baby.

PGT is usually recommended when:

  • The woman is over 37.
  • There is a family history of aneuploidy.
  • There have been previous implantation failures.
  • There is recurrent pregnancy loss.

More information: Preimplantation Genetic Testing. If you want to learn more about Turner syndrome, we have useful details there as well.

Impact of aneuploidy on fertility and pregnancy

Around 35% of implantation failures in assisted reproduction treatments are due to aneuploid embryos. If you are considering IVF or you are over 37, genetic screening will help you choose embryos with better viability and reduce risks.

Avoid self-medicating. Always consult your reproductive specialist so your plan can be personalized and your chances optimized.

Frequently asked questions

1. How common is aneuploidy in embryos?

Close to 50% of embryos created through IVF are aneuploid, and the figure increases with maternal age: it reaches 70% at age 40. PGT selects euploid embryos, lowers the risk of miscarriage, and improves birth rates.

2. Can lifestyle prevent aneuploidy?

A healthy lifestyle (a diet rich in antioxidants, moderate exercise, avoiding tobacco and alcohol, managing stress) improves egg and sperm quality, but it does not prevent the chromosomal errors linked to age. For anyone over 37, genetic testing remains the most reliable option.

3. How effective is PGT at reducing miscarriage?

PGT can lower miscarriage rates by up to 50% in women over 35, because only euploid embryos are transferred. Overall, the live birth rate after PGT ranges between 60% and 70% per transfer.

Consult an assisted reproduction specialist before making any decision.

4. What are the risks of PGT?

PGT involves a small embryo biopsy, with minimal risk. Thanks to current technology, more than 98% of embryos survive the procedure. It is essential that experienced embryologists perform it and that you discuss risks and benefits with your specialist.

Sources consulted

  1. Hassold, T., & Hunt, P. (2001). To err (meiotically) is human: the genesis of human aneuploidy. Nature Reviews Genetics, 2(4), 280-291. https://doi.org/10.1038/35066065
  2. Ramía, M., Musharrafieh, U., Khaddage, W., & Sabri, A. (2014). Revisiting Down syndrome from the ENT perspective: review of literature and recommendations. European Archives of Oto-Rhino-Laryngology, 271(7), 1795-1804. https://doi.org/10.1007/s00405-013-2554-4
  3. Rubio, C., Bellver, J., Rodrigo, L., et al. (2017). In vitro fertilization with preimplantation genetic diagnosis for aneuploidies in advanced maternal age: a randomized, controlled study. Fertility and Sterility, 107(5), 1122-1129. https://pubmed.ncbi.nlm.nih.gov/28433371/
  4. MedlinePlus. (2023). Aneuploidy. U.S. National Library of Medicine. https://medlineplus.gov/genetics/understanding/testing/aneuploidy/

We are with you on this path. Every case is unique: see a fertility specialist for the best guidance and personalized support.