prævia

Placenta previa is an obstetric condition in which the placenta implants in the lower part of the uterus near or over the opening of the cervix (the internal os). The name comes from Latin praevius, meaning in front of or preceding, reflecting the placenta’s position relative to the cervical opening.

Classification varies, but most commonly: complete placenta previa (the placenta completely covers the internal os); partial placenta previa (the placenta covers part of the os); marginal placenta previa (the placenta’s edge reaches the margin of the os); and low-lying placenta (the placenta is near the os but not covering it). The exact definitions can differ by guideline or imaging threshold.

Diagnosis is typically made by ultrasound, often first by transabdominal scanning and then clarified with transvaginal ultrasound to measure the distance between the placental edge and the internal os. In many cases, placenta previa is first suspected after painless vaginal bleeding in the second or third trimester. MRI is rarely needed but may be used in complex cases.

Risk factors include prior cesarean delivery or other uterine surgery, multiparity, advanced maternal age, smoking, and multiple gestation. Placenta previa increases the risk of maternal hemorrhage during pregnancy and delivery, preterm birth, and may be associated with placental abnormalities such as placenta accreta spectrum.

Management depends on gestational age, bleeding, and placental location. If the placenta covers the os and there is bleeding or if the pregnancy is near term, delivery is usually by cesarean section. Vaginal delivery is generally avoided when the placenta covers the os. In stable cases with mild bleeding and a non–covering placenta, expectant management with careful monitoring may be considered, often with hospitalization and activity modification. Rh status and fetal well-being are routinely assessed as part of care.