The Difference Between Mosaicism and Aneuploidy

In the field of reproductive medicine, the emergence of advanced techniques such as embryo biopsy has revolutionized the way we approach fertility treatments. Two terms that frequently come up in this context are “mosaicism” and “aneuploidy.” These terms refer to different genetic conditions that can be identified through embryo biopsy.

What Does Mosaic Mean in IVF?

When an embryo is biopsied, a small sample of cells is taken from it for genetic testing. Mosaicism occurs when the cells of an embryo have different genetic compositions. This means that some cells may have a normal number of chromosomes, while others may have extra or missing chromosomes. Mosaicism can occur naturally during early embryonic development and is sometimes associated with genetic disorders or developmental abnormalities.

What Happens When Aneuploidy Occurs?

On the other hand, aneuploidy refers specifically to an abnormal number of chromosomes in an embryo. In a normal embryo, each cell should contain the correct number of chromosomes (46 in humans). However, aneuploid embryos have either too many or too few chromosomes, which can lead to miscarriage or birth defects if implanted and allowed to develop.

Mosaicism vs. Aneuploidy

The main difference between mosaicism and aneuploidy lies in the genetic makeup of the cells. Mosaicism refers to the presence of cells with different genetic compositions within an embryo, while aneuploidy refers to an abnormal number of chromosomes in all or most of the cells.

How Successful is IVF With Aneuploid or Mosaic Embryos?

Both mosaicism and aneuploidy can impact the success rates of fertility treatments such as in vitro fertilization (IVF) and preimplantation genetic testing (PGT). Identifying these genetic conditions through embryo biopsy allows fertility specialists to make informed decisions about which embryos are most likely to result in successful pregnancies. Embryos with severe aneuploidy or genetic disorders may be discarded, while those with mild or moderate mosaicism may still be considered for transfer based on individual circumstances and expert recommendations.

Mosaicism and aneuploidy are distinct genetic conditions that can be identified through embryo biopsy. While mosaicism refers to the presence of cells with different genetic compositions within an embryo, aneuploidy specifically refers to an abnormal number of chromosomes in all or most of the cells. Understanding the difference between these conditions is important for making informed decisions in reproductive medicine and improving the chances of successful pregnancies.