Introduction: The prevalence of breech presentation ranges from 6.9% to 10.0% between weeks 32 and 36 of gestation, gradually declining to 3.0-5.0% by the time an external cephalic version (ECV) can be offered. The primary objective of our study was to identify the factors favoring a spontaneous version between the routine third-trimester ultrasound and the proposal of external cephalic version. We also compared the maternal and neonatal outcomes at delivery between fetuses who spontaneously turned to the cephalic presentation and those who were in the cephalic presentation after external cephalic version.

Method: This retrospective observational study included pregnant women with a breech fetus at their third trimester ultrasound scan (around 32 WG), who were under the care of a tertiary hospital between 2003 and 2022.

Results: A total of 2,439 women were included in the study. The rate of spontaneous version between 32 and 36-37 weeks was 65%. The favoring factors, after adjustment, were multiparity, maternal age under 25 years, polyhydramnios. No difference was found in the incidence of cesarean section (12.6% vs. 13.2% p  = 0.32) or assisted vaginal delivery (12.1% vs. 13.0% p  = 0.72) for fetuses lying in the cephalic presentation after external cephalic version, compared to those with spontaneous version into the cephalic presentation after third trimester scan.

Conclusion: The risk factors for a fetus remaining in the breech presentation after 32 weeks of gestation were similar to those associated with breech presentation in general. There was no difference in maternal or fetal outcomes between fetuses that were spontaneously or non-spontaneously versed fetuses (after external cephalic version).