Dizygotic Twins (DZ twins)

Definition - What does Dizygotic Twins (DZ twins) mean?

Dizygotic twins are twins that develop from two eggs being fertilized by two seperate sperm and implanting in the uterus at the same time. They are no more related to each other than any other biological sibling and are the most common type of twins. Fertility treatments and drugs can cause a woman to become pregnant with dizygotic twins far more frequently than would occur naturally.

Dizygotic twins are also know as fraternal twins.

FertilitySmarts explains Dizygotic Twins (DZ twins)

All dizygotic twins are dichorionic-diamniotic twins, meaning they each have their own placenta and amniotic sac. Because they aren’t sharing a placenta or amniotic sac (like monochorionic-monoamniotic or monochorionic-diamniotic twins), they run little risk of compressing or becoming entangled in each other’s umbilical cords, both situations that can cause critical harm. Like any type of twins, dizygotic twins are expected to be born prematurely, likely at 37 weeks rather than at 40 weeks. Low birth weight from sharing the mother’s resources, along with premature birth can increase the danger of health issues, but dizygotic twins have the best odds of survival of all types of twins, at about 91%.

Some women carry a gene that makes them much more likely to ovulate more than one egg per menstrual cycle. Therefore, the chances of having dizygotic twins comes from with the mother’s genetics, even if twins run in the father’s family. Conversely, scientists do not know of any genetic factor in producing identical twins. Other factors that increase the likelihood of dizygotic twins includes the age of the mother (over age 35, the chances of having twins doubles), mother’s nutrition, the number of births the mother has already had, and any fertility drugs or treatments the mother may have undergone. While dizygotic twins occur in 0.67% of natural pregnancies, about 35% of in-vitro fertilization (IVF) pregnancies are twins.

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