Sarah and Siaboo the orangutans -- are due about a month apart. Keepers have trained the "moms to be" to participate in the regular ultrasounds -- by coaxing them with treats.
The goodies get them to stand still at the front of the cage during the procedure. And instead of regular gel -- Siaboo prefers a blend of avocadoes on her belly.
Zoo experts got a fairly good look at the newborns on the monitor, although the primates were a little skittish.
Doctors will attend the births this fall -- but won't intervene unless the mothers need help.