When should external cephalic version be performed?

External cephalic version (ECV) is a procedure used to turn a fetus that is in a breech or transverse position into a head-down (cephalic) position, which is more favorable for vaginal delivery. The optimal timing for performing ECV is after 36 weeks of gestation, specifically around 37 weeks. This timing allows for the fetus to have sufficient fetal maturity while also taking advantage of the space available in the uterus to facilitate the manipulation of the fetus.

Performing ECV before 36 weeks may not be advisable due to the increased risk of complications and lower likelihood of success, as the fetus is not fully matured, and the amniotic fluid level may not be as conducive to a successful version. Waiting until 40 weeks is often too late since the risks and complications associated with possible delivery or fetal distress increase closer to labor. Additionally, attempting ECV during labor is generally not recommended because it could lead to complications, such as fetal heart rate decelerations or increased stress to the fetus.

Thus, the rationale for performing external cephalic version after 36 weeks strikes a balance between ensuring fetal maturity and maximizing the chances of success while maintaining safety for both the mother and the fetus.