Skip to content

    Health & Pregnancy

    Font Size
    A
    A
    A

    Twin Pregnancy Types

    h9991443_001.jpg

    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 amniotic sac.

    Fraternal twins develop when two eggs are fertilized by two separate sperms. The fetuses have separate placentas and amniotic sacs.

    ByHealthwise Staff
    Primary Medical ReviewerSarah Marshall, MD - Family Medicine
    Specialist Medical ReviewerWilliam Gilbert, MD - Maternal and Fetal Medicine

    Current as ofNovember 14, 2014

    WebMD Medical Reference from Healthwise

    Last Updated: November 14, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

    Pregnancy Week-By-Week Newsletter

    Delivered right to your inbox, get pictures and facts on
    what to expect each week of your pregnancy.

    Today on WebMD

    hand circling date on calendar
    Track your most fertile days.
    woman looking at ultrasound
    Week-by-week pregnancy guide.
     
    Pretty pregnant woman timing contaction pains
    The signs to watch out for.
    pregnant woman in hospital
    Are there ways to do it naturally?
     
    slideshow fetal development
    Slideshow
    pregnancy first trimester warning signs
    Article
     
    What Causes Bipolar
    Video
    Woman trying on dress in store
    Slideshow
     
    pregnant woman
    Article
    Woman looking at pregnancy test
    Quiz
     
    calendar and baby buggy
    Tool
    dark chocolate squares
    Slideshow