LISTEN ABOVE: The director of the Twin Studies Center at California State University explains why all same-sex twins should get genetic testing.

Are you a twin? And if so, do you know with confidence whether you are an identical or fraternal twin?

Many parents rely on the results of an ultrasound. If there are two placentas, they assume they are carrying fraternal twins, and if there is one placenta, it’s assumed the twins are identical.

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