Polyspermy

Definition - What does Polyspermy mean?

Polyspermy is a condition where an egg is fertilized by more than one sperm cell. This can happen due to abnormalities of the formation of natural barriers after an egg has been fertilized by one sperm. It could also be the result of too many sperm cells reaching the egg and engaging in a strong competition to penetrate the egg, a situation more commonly seen during in vitro fertilization (IVF).

In polyspermy, the resulting cell after fertilization contains more than two sets of chromosomes and does not develop into a healthy embryo. Polyspermy can delay a woman from getting pregnant, causing infertility or reduce the success rates of reproductive techniques such as in vitro fertilization.

FertilitySmarts explains Polyspermy

Human cells contain 46 chromosomes as 2 sets (diploid cells), and during the formation of germ cells, the egg and the sperm only get one set of those chromosomes. During fertilization, the egg fuses with one sperm and the two sets of chromosomes from both biological parents couple to form the embryo with cells having 46 chromosomes. Cells that contain more than 2 sets of chromosomes (polyploid cells) are not able to survive. Most pregnancies that are formed by polyploid cells end as miscarriages and the very few that may survive typically do not live beyond childbirth.

Naturally, when a single sperm binds to the outer membrane of the egg, natural cellular mechanisms activate to prevent further sperm cells from entering the egg. Soon after fertilization, a voltage barrier is activated in the outer layer of the egg that prevents any additional sperm from binding. This happens within seconds and therefore called the 'fast block' of polyspermy. During the 'slow block' of polyspermy that happens 5-8 minutes after fertilization, the egg releases enzymes that alter the zona pellucida, the outer layer of the egg, and a wall is formed surrounding the egg that stops more sperm from penetrating the egg. Defects of these mechanisms, or simply too many strong sperm cells competing to enter the egg can give rise to polyspermy.

During artificial fertilization of the egg during in vitro fertilization (IVF), there is a chance of an egg being fertilized by more than one sperm. This can make the procedure ineffective, requiring repeated attempts at fertilization, leading to an additional investment of time and money.

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