Fraternal Twins

Fraternal Twins

Fraternal twins are the most common type of twinning, also known as Dizygotic or Non-Identical Twins. This happens when two eggs have been released called hyperovulation, which are then fertilized independently, by two separate sperm.


More Facts About Fraternal Twins


  • How common are they?
    Dizygotic Twins are more common than identical twins. The most common is boy/girl twins which makes up nearly half of all twins born, about 40%. In total non-identical twins including fraternal girl/girl and boy/boy twins make up about 75% of all twin births. Next in order of most to least common are fraternal girls, fraternal boys, identical girls then identical boys.
  • Have you heard the term Dichorionic Diamniotic twins?
    This means each baby has it’s very own placenta and amnionic sacs. Fraternal twins are always Dichorionic Diamniotic or commonly known as Di/Di twins even if it appears they have one placenta. This just means the two placentas have fused together but they still work separately. In some cases identicals can also be Di/Di twins.
  • Why are boys less common?
    Generally speaking non-identical boys and in fact all boys twins or not are weaker the fetus more so than girls. It is thought this is because when the mother is under any type of stress a women’s liver produces a hormone called cortisol. This hormone cortisol is very damaging to a male fetuses which can cause a miscarriage, but a female fetuses seems to be completely unaffected by this.
  • Geographically…
    Looking geographically Africa has the highest incidences of dizygotic twinning while Asia has the lowest. People say in some African tribes the consumption of yams has some effect on conceiving multiples.
  • Are they hereditary?
    While identical twins are in no way hereditary, dizygotic twinning can run in the family. In saying that there are women who fall pregnant with dizygotic twins with no history of multiples in their family.
  • Statistics…
    It is more common for older women to fall pregnant with non-identical multiples. Of mothers who become pregnant over the age of 45, 17% of those have multiples. Other factors that researchers have said to increase the likelihood of having twins are women who are taller, who have had a number on pregnancies and who are overweight.
  • What about their genes?
    Non-identical twins are basically siblings that share a birthday. Though they share about 50% of their genes, they can look very different or can sometimes be mistaken for monozygotic, identical twins.
  • Fertility treatments…
    Fertility drugs and treatments like IVF can increase the chance of having twins slightly.
  • Increasing your chances…
    Once you have had non-identical twins then it is said you are twice as likely to have them again.

Have you got any further questions, then check out our Twin Pregnancy FAQs

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