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Expert Q&A
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| By Randy Morris Board Certified Reproductive Endocrinologist, Chicago | ||
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I am looking for information in regards to what they call double ovum twins, or one egg with two yolks. How is it possible for a single egg to be fertilized with both a female and male child? From what I have been told when an egg is fertilized it only lets in one sperm to fertilize the egg.?
I have never heard or seen the term "double ovum twins." The most common type of twin pregnancy is when two separate eggs (ovum) are each fertilized with a separate sperm. Each develops its own yolk sac with its own umbilical cord, gestational sac and placenta. They are referred to as dizygotic (non-identical) twins.
A less common type of twins is when a single egg is fertilized with a single sperm. At some point after fertilization, the zygote or embryo splits in two. These are referred to as monozygotic (identical) twins. Monozygotic twins may rarely grow in the same sac together. It is possible that they could share a placenta or yolk sac. They would still have separate umbilical cords.
An egg doesn't have a yolk sac. A yolk sac is a structure seen when performing ultrasound on a developing embryo. It is not part of the fetus but rather a nutrient-containing structure that the fetus can feed off of until the placenta is developed. If two yolk sacs are seen within a single gestational sac, it could be a remnant from a twin pregnancy in which one of the twins was lost or failed to develop. It is also possible to have a double yolk sac that arose from a single fetus.
When an egg is fertilized by a sperm, there is a process called a cortical reaction that usually prevents additional sperm from penetrating the egg. It is possible, however, for more than one sperm to penetrate an egg. This is called polyspermic fertilization. These abnormally-fertilized eggs typically don't develop at all. If they do, it could develop into an abnormal type of pregnancy called a molar pregnancy in which no fetus develops. It is also possible that it develops into a fetus with too many chromosomes that ultimately miscarries
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More Answers by this Expert
- How can I prepare for conception? Is there any truth to cranberries contributing to uterine health?
- Can a chronic urinary infection affect my chances of conception?
- Why can't fallopian tubes be transplanted?
- What are double ovum twins?
- I'm 39 years old. I've heard that the older you get, your eggs start splitting, increasing your odds of a multiple birth (which I would be very grateful for). Is it likely that I would have a multiple birth?