Stability of first twin presentation in the late third trimester and its implications for delivery planning: a retrospective cohort study

INTRODUCTION: Fetal presentation of the first twin plays a key role in delivery planning. While vertex presentation is considered favorable for vaginal delivery, presentation changes may occur during the third trimester. However, the factors influencing these changes-particularly in relation to chorionicity-remain poorly defined. MATERIAL AND METHODS: This was a retrospective cohort study including 263 twin pregnancies (166 dichorionic diamniotic (DCDA), 97 monochorionic diamniotic (MCDA)) followed at a tertiary center between 2000 and 2025. Third-trimester ultrasounds were performed at 32 weeks and prior to delivery. We evaluated changes in the presentation of the first twin and analyzed variables that may be associated with fetal dynamics or stability, including parity, amniotic fluid volume, placental location, estimated fetal weight, and second twin presentation. RESULTS: The first twin maintained the same presentation in 53.6% of DCDA and 57.7% of MCDA pregnancies. Among those initially non-vertex, a spontaneous change to vertex presentation occurred in 53.4% of DCDA and 71.4% of MCDA cases. No statistically significant associations were found between presentation changes and the maternal or ultrasound-related variables studied. When vertex presentation was observed in the third trimester, it remained stable in over 95% of cases. CONCLUSIONS: The presentation of the first twin remains dynamic throughout until delivery, especially in non-vertex cases. However, a vertex presentation after 32 weeks is highly predictive of stability until delivery. Serial third-trimester ultrasound are essential for accurate delivery planning and should guide shared decision-making with expectant parents.