This article about turning a posterior baby is written by Hannah Dahlen

Midwives have traditionally encouraged women whose babies are lying in a posterior position (baby facing the mother’s back) to use a hands and knees position and pelvic rocking exercises during pregnancy to try and help rotate the baby into an anterior position (baby facing the mother’s front). A large Australian study published in the British Medical Journal in January 2004 indicated that several minutes a day of hands and knees exercises with pelvic rocking from 37 weeks of pregnancy until the onset of labour did not reduce the incidence of a posterior baby or babies lying in a posterior position. Posterior positions occur in around 10 to 25 out of 100 pregnancies. It continues to persist in labour in around 6 out of 100 women.

Posterior positions in labour can lead to more painful labour with a greater need for forceps or caesarean delivery. In labour women with babies in posterior positions are also encouraged to spend time on their hands and knees to encourage rotation and ease backache. Because you have the added force of contractions it is likely this is more effective than spending time on your hands and knees during pregnancy.