Recommendations
2. Sonographers are encouraged to report the actual dis
-
tance from the placental edge to the internal cervical os at
TVS, using standard terminology of millimetres away
from the os or millimetres of overlap. A placental edge
exactly reaching the internal os is described as 0 mm.
When the placental edge reaches or overlaps the internal
cervical os on TVS between 18 and 24 weeks’ gestation
(incidence 2–4%), a follow-up examination for placental
location in the third trimester is recommended. Overlap
of more than 15 mm is associated with an increased
likelihood of plaenta previa at term. (ll-2A)