If one egg is fertilized by two sperm, it results in an abnormal number of chromosomes, a condition known as triploidy.
Understanding Triploidy
Normally, a human egg and sperm each contain 23 chromosomes. Upon fertilization, these combine to create a zygote with 46 chromosomes (23 pairs), the standard genetic blueprint for a human being. However, when two sperm fertilize one egg, the resulting zygote has 69 chromosomes (three sets of 23), instead of the usual 46. This is triploidy.
Consequences of Triploidy
Triploidy is almost always fatal.
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Early Miscarriage: The vast majority of triploid pregnancies end in miscarriage during the first trimester.
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Severe Birth Defects: In rare cases where the pregnancy continues beyond the first trimester, the fetus exhibits severe birth defects. These can include heart defects, brain abnormalities, and malformations of the limbs. Survival beyond birth is extremely rare, and if it occurs, it is usually only for a very short period.
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Partial Molar Pregnancy: Sometimes, triploidy can lead to a partial molar pregnancy, a type of gestational trophoblastic disease. In this condition, the placenta develops abnormally, forming a mass of cysts. It can sometimes be associated with cancerous changes.
Why Does This Happen?
While the exact reasons for polyspermy (fertilization by more than one sperm) are not fully understood, factors that can increase the risk include:
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Delayed Fertilization: If the egg is "overripe" (i.e., not fertilized soon enough after ovulation), its protective mechanisms against multiple sperm entering may be less effective.
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In Vitro Fertilization (IVF): There is a slightly increased risk of polyspermy with some IVF techniques.
In Summary
The fertilization of an egg by two sperm leads to triploidy, a condition where the embryo has 69 chromosomes instead of the normal 46. This almost always results in miscarriage or severe birth defects and is rarely compatible with life.
