PREDICTION OF PLACENTA PREVIA AT DELIVERY
The occurrence of placenta previa is common in the first
half of pregnancy, and its persistence to term will depend on
the gestational age and the definition employed for the
exact relationship of the internal cervical os to the placental
edge on TVS.
21–26
In this guideline, the following terminology is recommended to describe this relationship: when the
placenta edge does not reach the internal os, the distance is
reported in millimetres away from the internal os; when the
placental edge overlaps the internal os by any amount, the
distance is described as millimetres of overlap. A placental
edge that exactly reaches the internal os is described by a
measurement of 0 mm.