19. How can I tell if my multiples are identical or fraternal?

To determine zygosity, your doctor may look (around 12-18 weeks gestation) for separate and distinct sacs as well as separate and distinct placentas for each fetus. Unfortunately, this method can only confirm identical multiples when more than one infant shares an amniotic sac and/or sometimes a placenta. Because identical multiples can also appear separately, mono-zygosity cannot be ruled out if separate sacs and placentas are seen.

Unless zygosity is confirmed through a shared amniotic sac or placenta (not just a merged placenta which can sometimes happen with fraternal multiples), the only definitive way to know zygosity is to test the placentas at the time of delivery or to DNA test each child after birth.

One way parents of identical multiples can meet other families of identical multiples is through the MOST Family Support Forums.

The Mom 2 Many website offers more detailed information on zygosity testing.

Zygosity Chart

Identical versus Fraternal Quiz

FAQ on Zygosity

Twin Services article "The Alphabet Soup of Twin Biology"

MOST also offers our book Expecting Multiples: A Comprehensive Guide covering a variety of topics related to pregnancy and delivery of higher-order multiples.

Please Note:
MOST provides these FAQs for informational purposes and cautions visitors not to use the content below to make treatment decisions without personally consulting a qualified health care provider. Reuse of this content without proper citation is a violation of copyright. To obtain permission to use Supertwins 101 content contact MOST.

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Copyright MOST 2005                                                     Updated 9/14/10