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Identical twins come from a single fertilized egg that divides in half.

  • Thirty percent of twins are identical.
  • Identical twins are the same sex and have the same genetic makeup.
  • They may share amniotic sacs and placentas, or be separate.

Fraternal twins come from two eggs fertilized by two sperm.

  • Although they are born at the same time, fraternal twins are no more alike than other brothers and sisters born to the same parents.
  • Inside the mother, fraternal twins are surrounded by separate sacs. They have separate placentas, although sometimes the placentas may grow together.
  • Fraternal twins are more likely to be born to:
    • Women 35 and over
    • Women who have already had twins
    • Women who become pregnant soon after stopping birth control pills
    • Women for whom twins run in the family

Risks from carrying twins

  • Preterm delivery due to early labor or early rupture of the membranes
  • Preeclampsia (high blood pressure, protein in the urine, and/or swelling)
  • Gestational diabetes
  • Anemia
  • Poor fetal growth
  • Increased blood loss with delivery
  • Cesarean section, if one of the twins is not coming out headfirst
  • Because twin pregnancies are more likely to have complications, you may be more likely to need bedrest or hospitalization.

Birth and beyond

  • Breastfeeding is usually possible with twins, and the body adapts by making more milk.
  • There are special pillows and techniques for breastfeeding twins.
  • Dartmouth-Hitchcock has lactation consultants who can help you with any breastfeeding questions you may have.
  • There are local support groups for mothers of twins.

Other resources

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