Fig. 4 a.

to d Pathological cord insertions. a Velamentous insertion at the end of the first trimester. The UC insertion is demonstrable opposite the chorion frondosum. b Transvaginal view of the same pregnancy as in a. A velamentous vessel runs directly across the cervical os (≙ vasa praevia). c and d Demonstration of velamentous vessels in the second trimester: c Longitudinal section. d Transverse section. These findings must always be followed by further assessment of placental UC insertion (to exclude velamentous insertion) and examination of the lower uterine segment (to exclude vasa praevia). Caption: chorion frondosum/placenta (*); cord insertion (→); cervical canal (▸).