The phrase "posterior baby" refers to a baby's position in the womb during childbirth. It means that the baby is facing the mother's abdomen instead of facing her back. Full definition
The high numbers of posterior babies at the end of pregnancy and the early phase of labor is a change from what was seen in studies over ten years old. (spinningbabies.com)
While most posterior babies do eventually rotate, that can still mean there is quite a long wait - and a lot of physical labor during that wait. (spinningbabies.com)
I found the experience of a very intense labour with uterine hyperstimulation on Synt / Pitocin, a big posterior baby, episiotomy and Ventouse with only partial local anaesthesia barbaric and quite horrifying. (skepticalob.com)