Spontaneous Version of Fetal Presentation in Twin Pregnancies During Third Trimester: Longitudinal Assessment.

Little is known about longitudinal changes of the first twin presentation in twin gestations. This is a retrospective cohort study including 411 women who were admitted consecutively and delivered live-born twins at 36 weeks of gestation or more. Longitudinal assessment of the first twin presentation was conducted during gestation and at birth in all cases. Gestational age at antenatal assessment was divided into two intervals: early-third trimester (28-31 weeks) and mid-third trimester (32-35 weeks). Fetal presentation was categorized as vertex or non-vertex. We analyzed change of fetal presentation between antepartum intervals and birth. First twin presentation at early-third trimester had the same presentation at birth in 87.6% (360/411) of the study population. In this 'no change' group, vertex presentation was seen in 95.6% (283/296) and non-vertex was seen in 67.0% (77/115) of cases. In total, 96.1% (395/411) of the study population maintained their presentation between mid-third trimester and birth. Vertex presentation was seen in 98.4% (310/315) and non-vertex was seen in 88.5% (85/96) of cases. When comparing vertex with non-vertex, vertex presentation during third trimester was a more reliable predictor of presentation at birth (p < .001). The only factor that contributed significantly to spontaneous version of the first twin during mid-third trimester and birth was a lower birth weight of the first twin compared with the second twin. In conclusion, first twin presentation with vertex during third trimester is not likely to change into non-vertex at birth. We concluded that vertex presentation in twin gestations at early- and mid-third trimester is very predictable. In contrast, a non-vertex first twin presentation is relatively unstable.