Placenta previa and vasa previa: Clinical sciences

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Introduction0:00–0:45

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.

Unstable patient0:45–5:19

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.
As for the labs, they usually reveal anemia and possible thrombocytopenia, as well as elevated PT, INR, and PTT, and low fibrinogen as coagulation factors are consumed.
Finally, an ultrasound will show the placenta either covering the cervical os or within 20 millimeters. This makes the diagnosis of placenta previa with hemorrhage and shock.For treatment, start IV fluids and prepare to give blood transfusions, if needed.
Deliver the patient by emergent c-section with immediate cord clamping, and give Rh immunoglobulin to Rh-negative patients to prevent rhesus alloimmunization in future pregnancies.
Now that we’ve talked about bleeding from a maternal source, let’s look at fetal blood loss from a vasa previa. In this case, bleeding occurs because the fetal blood vessels are unprotected and at risk for rupture and compression when the cervix dilates or the membranes rupture.
There could be evidence from an earlier ultrasound so consider risk factors such as velamentous cord insertion, meaning there are membranous umbilical vessels at the placental insertion site; marginal cord insertion, where the umbilical cord is inserted at or near the placental margin; succenturiate placenta, which is a placenta with one or more smaller accessory lobes; and in vitro fertilization.On a physical exam, maternal vital signs are typically normal.
Vaginal bleeding may persist or stop spontaneously. Assess fetal heart rate for a sinusoidal pattern that occurs with fetal anemia, or for sudden bradycardia with fetal decompensation.
Expect normal labs, and if you have time for an ultrasound, it may show fetal vessels crossing or within 20 mm of the os.
In this case, the diagnosis is lacerated vasa previa with fetal hemorrhage. When it comes to treatment, perform an emergent c-section with immediate cord-clamping to prevent ongoing blood loss.
Additionally, the neonate will often require immediate transfusion with type O-negative blood. Finally, provide maternal Rh immunoglobulin if they are Rh-negative.
Now that we’ve covered unstable patients, let’s move on to stable ones. Start with a focused history and physical exam.

Stable patient5:19–6:50

First, check if your patient has already had a second-trimester ultrasound, as this may have detected a placenta previa or vasa previa.
On the other hand, they may present with painless vaginal bleeding. Here’s a clinical pearl!
Painless vaginal bleeding in the second or third trimester often indicates a placenta previa, whereas painful vaginal bleeding typically comes from placental abruption.Now, risks for placenta previa include high parity, prior- c-section, prior uterine surgery, advanced maternal age, multiple gestations, smoking, and in vitro fertilization.
On the flip side, vasa previa should be suspected if an ultrasound demonstrates a velamentous cord insertion, marginal cord insertion, or succenturiate placenta; or if they had in vitro fertilization.
In both cases, vasa previa and placenta previa, the physical exam is often unremarkable. With these findings, you can suspect either placenta previa or vasa previa.
To confirm your suspicions, you’ll need some imaging. If they haven’t yet had their second-trimester fetal anatomic survey, be sure to perform one now, and consider transvaginal imaging with color and pulse wave Doppler for better visualization of fetal vessels.Let’s talk more about the imaging findings..

Vasa Previa6:50–7:40

Now, if ultrasound demonstrates unprotected fetal blood vessels that cross the internal cervical os or are within 20 millimeters, diagnose vasa previa.
Treatment starts with pelvic rest, which means refraining from using tampons or engaging in sexual intercourse. Plan on administering corticosteroids for fetal lung maturity between 28 to 32 weeks of gestation.
Consider hospitalization between 30 to 34 weeks because bleeding from vasa previa is massive and the fetus could exsanguinate.
Lastly, plan on a c-section delivery from 34 to 37 weeks gestation; however, you may need to deliver sooner if their membranes rupture or if they go into labor.Now, if the ultrasound demonstrates the placenta is covering the internal os or is within 20 millimeters, we are talking about either a placenta previa or a low-lying placenta.

Placenta previa or low-lying placenta7:40–10:30

Treatment includes pelvic rest, with a return if vaginal bleeding or contractions occur. It’s possible for the placenta to move away from the cervix as the pregnancy develops, therefore, assess for resolution with an ultrasound at 32 weeks.
If the placenta is now more than 20 millimeters away, plan routine pregnancy care as the condition has resolved. Here's another clinical pearl!
Even though the placenta previa has resolved, take a good look at the lower uterine segment on ultrasound to assess for fetal vessels over the cervix because a resolved placenta previa may become a vasa previa.
Okay, back to the patient. If the placenta is within 20 millimeters away, this is called a low-lying placenta.
Assess the proximity of the placental edge to the cervix, as this influences your management. If the placenta is low-lying, but 11 to 20 millimeters away from the cervical os, the risk of bleeding is not as high, but still possible.
Consider placing them on pelvic rest, and have them return for any episodes of vaginal bleeding or contractions, and offer them a trial of labor at term.
During delivery, the fetal head applies pressure to the tip of the placenta, helping to prevent placental disruption. Watch them carefully, though, and remain prepared for an immediate c-section.On the flip side, in cases where the placenta is 10 millimeters or less from the os, the risk for bleeding is high.
Treatment includes pelvic rest with a return for assessment with any vaginal bleeding or contractions. Plan for a c-section between 36 weeks and 37 weeks 6 days gestation.
Alright, let’s go back to our 32-week ultrasound. If it shows the placenta is still covering the os, you can confirm placenta previa.
Continue pelvic rest and have them return for any vaginal bleeding or evidence of labor, and plan for a c-section between 36 weeks and 37 weeks and 6 days of gestation, or sooner if needed.Here’s a final clinical pearl!
Be cautious when delivering patients with a placenta previa or low-lying placenta that’s overlying a uterine scar, such as in those who have had a previous c-section.
These patients are at high risk for placenta accreta spectrum, which can cause life-threatening hemorrhage when attempting to deliver the placenta because it adheres to the uterine wall.

Review10:30–11:12

Alright, as a quick recap… Placenta previa, low-lying placenta, and vasa previa are placental disorders that can cause hemorrhage.
Treat unstable patients with placenta previa with IV fluids and possibly blood products while proceeding to the OR for immediate c-section.
Similarly, unstable patients with vasa previa should also be delivered right away. As for the stable patients with vasa previa, put them on pelvic rest and plan for a c-section.
If the placenta is low-lying but 11 millimeters or more from the os, you can offer a trial of labor. However, if the placenta is 10 millimeters or less from the os or completely covers it,