In most cases, yes. Placenta previa diagnosed during a second-trimester ultrasound resolves on its own before delivery. More than 98% of marginal cases and over 80% of complete cases clear the cervix by the third trimester, based on a study of over 360 pregnancies with a mean diagnosis around 18 to 19 weeks. The earlier in pregnancy it’s found, the more likely it is to move out of the way.
Why the Placenta Appears to Move
The placenta doesn’t literally slide upward. What happens is that the lower part of the uterus stretches and thins as pregnancy progresses, effectively pulling the uterine wall (and the placenta attached to it) away from the cervix. At the same time, a process called trophotropism causes the placenta to grow preferentially toward areas with the best blood supply, which is typically the top of the uterus. Tissue on the less-nourished lower portion gradually thins out. Together, these two forces make it look on ultrasound as though the placenta has migrated upward, when really the uterus has reshaped around it.
This remodeling happens most dramatically between 20 and 34 weeks, which is why a previa flagged at your anatomy scan often disappears by the time you’re rechecked later in pregnancy.
Marginal vs. Complete Previa
How much of the cervix the placenta covers matters a lot for your odds of resolution. A marginal previa, where the placenta reaches near or just touches the edge of the cervical opening, resolves in virtually all second-trimester diagnoses. A complete previa, where the placenta fully covers the cervix, still resolves more than 80% of the time when found before 22 weeks, but those odds drop the later it’s discovered and the more tissue sits over the opening.
Prior C-Section Lowers the Odds
If you’ve had a previous cesarean delivery, your chances of the previa clearing are lower. In a prospective study comparing outcomes, 90% of women without a prior C-section saw their complete previa resolve, while only 61% of women with a prior C-section experienced resolution. The combination of an anterior placenta (one attached to the front wall of the uterus, right over the old scar) and a prior cesarean was the worst scenario: complete previa persisted to delivery in more than half of those cases. Scar tissue in the lower uterine segment is thought to interfere with the normal stretching and blood flow changes that would otherwise move the placenta out of the way.
Whether the placenta sits on the front or back wall doesn’t affect resolution on its own. It only becomes a meaningful factor when scar tissue from prior surgery is involved.
How It’s Monitored
After an initial diagnosis, most providers schedule a follow-up ultrasound around 28 weeks. In one study, 62% of previas had already resolved by that scan. Even when clearance was confirmed at 28 weeks, most patients still had a repeat check around 32 weeks to be sure.
Current guidelines from several professional societies recommend follow-up imaging at 32 weeks, though some research suggests the 28-week scan alone may be sufficient for cases that have clearly resolved. Your provider will decide the schedule based on how much of your cervix was covered and whether you’ve had any bleeding.
Activity Restrictions While You Wait
If your previa hasn’t resolved yet and you’re not actively bleeding, you’ll likely be placed on some form of pelvic rest. That typically means no sexual intercourse, no tampons, and nothing inserted into the vagina. You may also be asked to avoid strenuous exercise, heavy lifting, squatting, and jumping, since these activities can trigger bleeding or contractions.
Some providers recommend modified bed rest at home for more significant cases. The restrictions can feel frustrating, especially when the previa is likely to resolve on its own, but the goal is to prevent a bleeding episode that could lead to an emergency situation before the placenta has time to move.
What Happens If It Doesn’t Resolve
When the placenta still covers the cervix in the third trimester, the main concern is painless, bright red vaginal bleeding. This can happen spontaneously with no obvious trigger, or it can be brought on by contractions, intercourse, or a medical exam. Some women don’t experience bleeding until labor begins. The bleeding comes from the placenta being stretched or partially separated as the cervix starts to change in late pregnancy.
A persistent previa means a cesarean delivery is necessary. When the placental edge overlaps the cervical opening at all, vaginal delivery isn’t safe. For low-lying placentas where the edge has pulled back but is still close, the distance matters: women whose placental edge sits more than 10 millimeters from the cervical opening can often deliver vaginally, with more than two-thirds doing so without increased bleeding risk. At 10 millimeters or less, the risk of hemorrhage during labor rises significantly.
Scheduled cesarean delivery for a persistent, uncomplicated previa is typically planned around 36 to 37 weeks. If bleeding episodes, labor, or other complications develop earlier, delivery may need to happen sooner. When early delivery is anticipated, corticosteroids can be given to help the baby’s lungs mature.