previa

Prevía is a term used in several languages with different meanings, but it is most commonly encountered in obstetrics in reference to placenta previa. The word itself comes from Latin prævia, meaning before or preceding. In non-medical contexts, previa can mean a preview or an earlier event, as in everyday language, such as a prelude or beforehand.

In obstetrics, placenta previa describes a condition in which the placenta implants in the lower part of the uterus near or over the internal cervical os. It is classified as marginal, partial, or complete (low-lying placentas fall under these categories as well). The hallmark symptom is third-trimester vaginal bleeding that is often painless. Placenta previa can pose risks to both mother and fetus, mainly through hemorrhage during delivery if the placenta covers the cervix.

Diagnosis is typically made by ultrasound, first transabdominal then transvaginal, to determine the placenta’s location relative to the os. Management depends on the amount of bleeding, placental position, gestational age, and fetal status. Stable cases near term are usually managed with planned cesarean delivery around 36 to 37 weeks. In cases of active bleeding or nonviable placental position, earlier delivery may be required. Digital vaginal examinations are avoided when previa is suspected due to bleeding risk.

Risk factors for placenta previa include prior cesarean delivery, other uterine surgeries, multiparity, advanced maternal age, smoking, and multiple gestations. Placenta previa increases the likelihood of preterm birth and maternal hemorrhage, and it is associated with placenta accreta spectrum in some pregnancies.