After 36 weeks. Patients who have completed 36 weeks of gestation are preferred candidates for external cephalic versions (turn the baby, if not head down). Generally, spontaneous versions are likely to have taken place by 36 completed weeks. If done prematurely, babies can revert back to breech. Also, if complications arise during an attempted version, emergency delivery of a term infant can be accomplished.
After 38 weeks. Turning the baby or external version should be done after 38 weeks. The baby's heart tracing should be good. You should not be in labor, your water should not be broken, your placenta should not be over your cervix, and you should be able to have a vaginal delivery in order to have a version. Generally versions are successful 75% of the time in turning the baby.