Skip to Content
Home > Wellness > Health Library > Twin Pregnancy Types
Identical twins come from a single egg that has been fertilized by
one sperm. For unknown reasons, the fertilized egg splits into two embryos
during the first stage of development. In the mother's womb (uterus), most
identical twins share the same placenta. (They get oxygen and nutrients from
the mother and get rid of wastes through the placenta.) But they usually grow
within separate amniotic sacs. In rare cases, identical twins share one
Fraternal twins develop when two eggs are fertilized by two separate
sperms. The fetuses have separate placentas and amniotic sacs.
ByHealthwise StaffPrimary Medical ReviewerSarah Marshall, MD - Family MedicineSpecialist Medical ReviewerWilliam Gilbert, MD - Maternal and Fetal Medicine
Current as ofNovember 14, 2014
Current as of:
November 14, 2014
Sarah Marshall, MD - Family Medicine & William Gilbert, MD - Maternal and Fetal Medicine
How this information was developed to help you make better health decisions.
To learn more, visit Healthwise.org
© 1995-2015 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.
Our interactive Decision Points guide you through making key health decisions by combining medical information with your personal information.
You'll find Decision Points to help you answer questions about:
Get started learning more about your health!
Our Interactive Tools can help you make smart decisions for a healthier life. You'll find personal calculators and tools for health and fitness, lifestyle checkups, and pregnancy.
Feeling under the weather?
Use our interactive symptom checker to evaluate your symptoms and determine appropriate action or treatment.