Childbirth stations

The animation follows the baby's progress through the mother's birth canal, marking the baby's childbirth stations by how her head lines up with specific points in the mother's bony pelvis.

These points are called vertex positions, and use the designations 3, 2, 1, 0, -1, -2 -3 in what obstetricians (OB/GYNs) call the 1/3 system.