The vast majority of placenta previa cases diagnosed during pregnancy resolve on their own. Over 98% of low-lying placentas and placenta previas identified in the second trimester clear before delivery, with only about 1.6% persisting at term. If you were flagged at your 20-week anatomy scan, the odds are strongly in your favor.
How likely yours is to resolve depends on the type of previa, how far the placenta overlaps the cervix, and when it was first detected. Here’s what the numbers actually look like.
Resolution Rates by Type
Not all placenta previa is the same, and the type matters a lot for predicting whether it will move. A marginal previa, where the placenta reaches the edge of the cervical opening but doesn’t cover it, resolves about 98% of the time when diagnosed in the second trimester. A complete previa, where the placenta fully covers the cervix, still resolves in over 80% of cases. Those are reassuringly high numbers for both types, though complete previa does carry a meaningfully higher chance of sticking around.
Why the Placenta Appears to “Move”
The placenta doesn’t actually detach and relocate. What happens is that the lower part of the uterus stretches and grows significantly during the second half of pregnancy. As this lower segment expands, the cervix effectively moves farther away from the placenta’s edge, making it look like the placenta migrated upward.
There’s also a process called trophotropism: the placenta preferentially grows toward the area of the uterus with the best blood supply, which is typically the upper portion (the fundus). At the same time, the portion of the placenta sitting over the thinner, less blood-rich lower segment can thin out and recede. Together, these two mechanisms account for the high resolution rates seen throughout the second and third trimesters.
How Distance From the Cervix Predicts Your Odds
One of the strongest predictors of resolution is how far the placenta sits from the internal cervical opening at the time of your anatomy scan. Research in the Journal of Ultrasound in Medicine broke this down clearly:
- 10 to 20 mm from the cervix (low-lying): 99.5% resolution rate. This is nearly guaranteed to clear.
- Within 10 mm of the cervix: 95.4% resolution rate. Still very likely to resolve.
- Covering the cervix (true previa): 72.3% resolution rate. Most still resolve, but roughly 1 in 4 persist.
In practical terms, the closer the placenta is to covering or overlapping the cervix at the midtrimester scan, the more follow-up you’ll need and the higher the chance it remains an issue.
When Diagnosis Happens Matters
Earlier detection generally means better odds of resolution, because the uterus still has significant growing to do. The persistence rates by gestational age at diagnosis paint a clear picture:
- 15 to 19 weeks: only 12% persist
- 20 to 23 weeks: 34% persist
- 24 to 27 weeks: 39% persist
- 28 to 31 weeks: 62% persist
- 32 to 35 weeks: 73% persist
The pattern is straightforward: a previa found at your 20-week scan has a much better chance of resolving than one still present at 32 weeks. By the third trimester, the lower uterine segment has already done most of its stretching, so there’s less room for the placenta to “migrate.”
What the Follow-Up Timeline Looks Like
After a previa is identified at the anatomy scan, your provider will schedule a follow-up ultrasound to check whether the placenta has moved. This typically happens around 28 weeks, though timing varies. At that first follow-up (median 28 weeks), about 77.7% of women show resolution.
For those who haven’t resolved by that point, another ultrasound follows later in the third trimester. Among women whose previa persisted at the first follow-up, about 71% went on to resolve at a later scan. Overall, the cumulative resolution rate across all follow-up ultrasounds reaches roughly 92%.
So if your 28-week scan still shows previa, that doesn’t mean it’s permanent. A significant portion of persistent cases continue to clear between 28 and 36 weeks, though the window narrows as you approach term.
What Happens If It Doesn’t Resolve
For the small percentage of cases where the placenta remains over or very close to the cervix, a cesarean delivery is planned at 36 to 37 weeks. This timing balances the baby’s lung maturity against the risk of going into labor spontaneously, which could cause dangerous bleeding with a previa in place.
In the weeks leading up to delivery, you may be advised to avoid strenuous activity and watch for vaginal bleeding, which is the hallmark symptom of a previa that hasn’t cleared. Some women with persistent previa experience no bleeding at all, while others may have episodes that require closer monitoring or even hospitalization.
One Complication Worth Knowing About
Even when placenta previa resolves, it can leave behind a slightly elevated risk for a condition called vasa previa, where fetal blood vessels run across or near the cervical opening without the protection of the placental tissue or umbilical cord. This is uncommon, but a history of resolved placenta previa or a low-lying placenta is a recognized risk factor. Your provider may keep this in mind during later ultrasounds, particularly if the placenta had a bilobed or irregularly shaped appearance.