When is a placenta considered low lying?

• A. When it covers the internal os
• B. When it is located less than 2 cm from the cervix
• C. When it is within 5 cm of the cervix
• D. When it lies posterior to the cervix

Answer: (B)

A placenta is considered low lying when its edge sits within a short distance of the internal cervical os but does not cover it. The key threshold is within 2 cm of the os; this proximity signals a placenta that is in the lower uterine segment and may affect delivery planning, but it hasn’t yet overlapped the opening. If the placenta covers the os, that’s placenta previa, which is a different, higher-risk situation. Being within 5 cm would be too broad to define low lying, and being located posterior to the cervix is not the criterion used to classify placental position. Ultrasound measures this distance to guide monitoring and potential delivery decisions.