dispermy

Dispermy, or polyspermic fertilization, is the fertilization of an oocyte by two sperm during a single fertilization event. The zygote produced commonly contains three haploid chromosome sets (triploidy), typically two paternal and one maternal genomes.

Normally, oocytes employ fast and slow blocks to polyspermy to prevent multiple sperm entry. When these barriers fail, a second sperm can contribute genetic material to the zygote. The resulting triploid state means the embryo or placental tissues carry two paternal chromosome sets and one maternal set.

Outcomes are generally incompatible with continued development. Most dispermic conceptions abort early in pregnancy. If implantation occurs, the pregnancy may be a molar pregnancy with an abnormal placenta and little fetal tissue, or a fetus with multiple congenital abnormalities associated with triploidy.

Clinical and research relevance: Dispermy accounts for a portion of human triploid conceptions, particularly in the context of assisted reproduction. It provides insight into the mechanisms that normally prevent polyspermy and the consequences of aberrant fertilization for embryonic development.