»  My friend said their doctor told them the zygosity of their twins based on a placental exam. Is this possible?  (Back)

The number of placentas does not predict zygosity. One third of monozygotic twins have two placentas and 42% of dizygotic twins have a single, fused placenta. Many obstetricians try to determine the zygosity based on how thick or thin the membrane between the two bags of water is, or by how easily it can be peeled apart. This is only accurate if a microscopic examination is done after special processing of the tissues. This examination is expensive and often inconclusive.

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