that-goddamn-owl: Well, if Elastigirl is able to stretch her body either wide open (the plane exploding) or far long (her infiltration to Syndrome's Base), I think it's safe to assume that her elastic properties go down beyond her bones and in fact affect the rest of her organs as well. The only thing she has not stretched out is her head though.

But does the umbilical cord count as part of her body?
Technically it is formed from Dash’s egg cells multiplying so it shouldn’t since it’s not the same genetic information contained in his DNA to allow him to have mom’s powers .-.