"...maybe one of a mother giving birth..." Careful, if the baby is in contact with the vagina, that would be a violation. Of course, if the mother was one of those multiparous women with strong pelvic muscles who can pop out babies with ease, you might capture the newborn in mid-air at the moment of delivery. Strangely, Zygote supposedly deigned to create an anatomically correct female for some OB/GYN job. So, you could argue that birth has been declared (ex cathedra no less) to be an acceptable reason for depicting yawning yoni.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken