Placenta previa and vasa previa: Clinical sciences

Placenta previa is when placental tissue partially or completely covers the internal cervical os. When the placental edge is within 20 millimeters of the internal cervical os but isn’t actually covering it, it’s called a low-lying placenta. In contrast, in vasa previa, the fetal vessels either cross the internal os or are within 20 millimeters of it. The etiologies are unknown, though each condition has independent risk factors. These entities are important because they can cause bleeding, especially in labor or when membranes rupture. In placenta previa, the source of bleeding is maternal, whereas bleeding in vasa previa comes from the fetus.

Your first step in evaluating a patient presenting with a chief concern suggesting placenta previa or vasa previa is to do a CABCDE assessment to determine if they unstable. Unstable patients may have heavy vaginal bleeding, so prepare for urgent surgical management. Stabilize the airway, breathing, and circulation, and intubate the patient if necessary. Obtain IV access, and continuously monitor their vital signs. Initiate continuous fetal heart rate monitoring, and check for any signs of labor. Perform a sterile speculum exam to assess the volume of bleeding and check visually if the cervix is dilated.

Keep in mind that you should never perform a digital cervical exam on a patient with placenta previa or vasa previa, as it can disrupt the placenta and vessels and worsen the situation.

After the primary assessment, obtain a focused history, physical exam, and labs including CBC, PT, INR, PTT, fibrinogen, and a type and crossmatch. You may also need to perform an ultrasound to help with diagnosis, but don’t delay treatment while waiting for imaging.

Let’s talk about the history of those with placenta previa. Your patient may report dizziness, tunnel vision, and anxiety due to the acute blood loss, which occurs when shearing forces from uterine contractions and cervical changes disrupt the placental attachment site. There could also be a known abnormal placental location from an earlier ultrasound.

There are conditions that raise the risk of placenta previa, such as high parity, history of a prior c-section or other uterine surgery, advanced maternal age, multiple gestations, smoking, and in vitro fertilization.

A physical exam might reveal hypotension, tachycardia, and altered mental status. They may appear pale, and their skin might feel cold or clammy. Typically, there will be painless vaginal bleeding, which could spontaneously resolve or it might be ongoing. With severe bleeding, you may find fetal bradycardia as well.