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Fraternal Twins: Equivalent vs. Fraternal Twins

What Are Fraternal Twins?

Fraternal twins, or dizygotic twins, occur when two totally different eggs are fertilized by two sperm. “Di” means two and zygotic refers back to the zygote, the egg fertilized by the sperm that can grow to be an embryo and develop right into a child.

Nearly all of twins are fraternal twins (twins which can be extra like siblings born on the identical time). Monozygotic twins, or similar twins, come from a single egg and sperm that splits into two after conception.

Study extra about fraternal twinning, from how they kind to how they relate to one another, in addition to how they differ from similar twins.

Odds of Conceiving Fraternal Twins

Fraternal twins kind in the identical method that each one people do, by the union of sperm and egg. Dizygotic twinning happens when multiple egg is launched throughout ovulation. This is called hyperovulation.

There are quite a few causes for hyperovulation, together with:

  • Peak: Taller folks have a higher-than-average price of dual pregnancies.
  • Excessive physique weight: Additional fats shops produce elevated ranges of estrogen, which can stimulate hyperovulation.
  • Maternal age: As you get older, you are extra more likely to hyperovulate.
  • Subsequent births: Individuals who have beforehand given beginning to a number of youngsters could also be extra more likely to have twins.
  • Race: The best charges of twinning are present in Central African populations, whereas Asia and Latin America have the bottom charges of twinning.

There are weaker anecodtal associations with utilizing contraception capsules, folic acid, and the season of the 12 months. None of those components have been confirmed to extend the possibilities of having similar twins.


An inclination towards hyperovulation is usually a genetic trait. On this method, fraternal twinning will be hereditary. A mom who has the gene for hyperovulation can go it all the way down to their daughter. Then, the daughter’s possibilities of having twins are elevated.

As a result of males carry each X (feminine) and Y (male) chromosomes, they’ll additionally maintain the trait for hyperovulation. They will go it alongside to their daughters too, growing their daughters’ possibilities of having fraternal twins.

If there are fraternal twins on each the mom’s and father’s sides, your odds for twins goes up even greater.

Nonetheless, having the gene for hyperovulation doesn’t improve a person’s possibilities of fathering fraternal twins. If a person carries the gene, it does not change the ovulation sample of the mom of their youngsters. They’ve their very own genes governing their ovulation. As an alternative, it will be the daddy’s daughter who inherits it via their dad’s genes. That’s the reason twins are generally assumed to “skip a era.”

Fertility Therapies

As medical expertise made fertility-enhancing remedies extra accessible, the dual beginning price has skyrocketed. Whereas not all remedies for infertility improve your odds of fraternal twins, many do, together with.

Curiously, whereas IVF normally leads to fraternal twins (as a result of switch of a number of embryos on the identical time), some cases of monozygotic twinning may happen.

Varieties of Fraternal Twins

As a result of fraternal twins kind from separate eggs and sperm, this could result in some unusual circumstances through which the twins have totally different gestational ages and even totally different fathers.


Typically, hyperovulation occurs a number of days aside. After one egg is fertilized and begins to journey to the uterus for implantation, one other egg is fertilized by sperm from a later incident of sexual activity. The result’s fraternal twins who’re conceived a number of days aside. This is called superfetation.


There have even been cases of fraternal twins with totally different fathers. This happens when an individual releases a number of eggs and has sexual relations with multiple accomplice. If an egg is fertilized by sperm from one particular person, after which one other egg is fertilized by sperm from a special particular person, the result’s fraternal twins with totally different fathers. This phenomenon is named superfecundation.

Placenta Fusion

Throughout being pregnant, the placenta gives very important sustenance to the child. In a a number of being pregnant with fraternal twins, a placenta develops for every child. Typically, nevertheless, the 2 placentas fuse collectively and look like one single placenta. Having a fused placenta will increase the prospect of low beginning weight and intergrowth discrepancy (through which one twin will get extra vitamins and oxygen from the placenta and grows greater than the opposite).

Nonetheless, as a result of they sometimes have their very own placentas, fraternal twins usually are not in danger for a number of the situations that have an effect on monozygotic twins, corresponding to twin-to-twin transfusion syndrome (TTTS) or monoamniotic twins.

Equivalent Twins vs. Fraternal Twins

Identical to different siblings, fraternal twins will share about 50% of their DNA. Every particular person receives half of their DNA from their mom’s egg and the opposite half from their father’s sperm, so any two offspring could have some overlapping qualities.

Monozygotic twins share the identical genetic make-up, or genotype (though their DNA isn’t essentially similar.) This shared DNA is what makes them typically have remarkably comparable appearances and traits.

Not like monozygotic twins, fraternal twins might look nothing alike, together with having totally different:

  • Eye coloration
  • Hair coloration
  • Personalities
  • Stature

Or, they could certainly be so comparable that they’re assumed to be similar, simply as some siblings could be remarkably indistinguishable in the event that they have been the identical age.

Twins and multiples are additionally formed by their setting after they’re born. Some similarities are enhanced as a result of they’re raised in the identical house, share the identical experiences, and are educated in the identical faculties on the identical time.


As a result of fraternal twins originate from separate conceptions, they’ll each be boys, each women, or one in every of every (identical to a singleton child). Chromosomes from the daddy’s sperm decide intercourse: XX for a woman and XY for a boy.

In consequence, the possibilities of fraternal twins leading to boys, women, or a mixture are the identical as for every other pair of siblings.

Monozygotic twins, then again, are at all times the identical intercourse, both two women or two boys.

Fraternal Twins (Dizygotic)

  • Come from their very own egg and sperm

  • Share about 50% of DNA

  • Might look very totally different

  • Could be a boy and woman, or the identical intercourse

Equivalent Twins (Monozygotic)

Well being Dangers

All pregnancies carry dangers for the pregnant particular person. Moreover, twins are affected by your well being and habits throughout being pregnant. Fraternal twins share elevated or decreased well being dangers as a consequence of sharing the being pregnant setting.

Being pregnant with twins places extra calls for in your physique in contrast with a singleton being pregnant and will increase the chance of the next:

  • Anemia
  • Delivery defects, together with neural tube defects and gastrointestinal and coronary heart abnormalities
  • Gestational diabetes
  • Miscarriage
  • Preeclampsia
  • Being pregnant-induced hypertension
  • Untimely beginning or preterm labor

Coping With a Twin Being pregnant

Whereas it is not doable to utterly get rid of the dangers that include having fraternal twins, you possibly can take some wholesome steps to cut back these dangers, together with:

  • Getting common prenatal care. Common prenatal care, ideally with a physician skilled in twin pregnancies, is important for catching any issues and receiving correct care.
  • Consuming effectively. Sustaining a nutritious diet and weight might help you are feeling your finest throughout being pregnant and assist guarantee your infants are born at a more healthy weight.
  • Staying hydrated. Dehydration is thought to set off untimely labor, which is extra seemingly once you’re carrying twins, so preserve that water bottle crammed.
  • Studying to acknowledge the indicators and signs of untimely beginning. If the indicators and signs of preterm labor are caught early sufficient, it could be doable to forestall it so you possibly can carry your being pregnant to time period and provides your infants a greater likelihood of survival.

A Phrase From Verywell

Your fraternal twins will share many issues all through their lives after beginning out within the womb collectively. Take pleasure in their similarities and variations as they develop. With these info, you can inform them how they really are distinctive.

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