By definition a low-lying placenta is a placenta whose edge is within 2 centimeters of the cervical opening. This should be distinguished from a placenta previa in which the placenta is actually covering the cervical opening. If the placenta persists in covering the cervix in the late third trimester, this can pose a risk of life-threatening bleeding and requires delivery by Cesarean section.

In contrast, a low-lying placenta (by definition) is not covering the cervix and should not interfer with vaginal delivery or necessarily pose an increased risk of vaginal bleeding. Of course there are some caveats to consider. Perhaps the most important is the precise wording of the report. Occasionally ultrasound reports will be evasive and not clearly indicate whether the placenta is a actually covering the cervix. If the ultrasound report is clear that the placenta is not over the cervix, our practice generally does not recommend specialized follow up or procedures unless the patient is actually bleeding. Of course, if one of our patients is having bleeding, we will generally follow her more closely regardless of placenta location.

Another consideration is gestational age. As the pregnancy progresses, the placenta covers less surface area of the uterus on a proportionate basis. As a practical matter, most placentas that are seen to be covering the cervix in early pregnancy will "move" up and away as the pregnancy progresses.