A low-lying placenta is one that sits within 20 millimeters of the cervix (the opening of the uterus) but doesn’t fully cover it. It’s typically discovered during the routine anatomy scan around 20 weeks of pregnancy, and it’s common: roughly 1 in 12 pregnancies show a low-lying placenta or placenta previa at that midpregnancy ultrasound. The good news is that the vast majority resolve on their own as the uterus grows.
How It Differs From Placenta Previa
The placenta normally attaches high on the uterine wall, well away from the cervix. When it implants lower than expected, doctors distinguish between two situations based on position. A low-lying placenta is close to the cervix (within 20 mm) but leaves some gap. Placenta previa means the placenta completely covers the cervix. The distinction matters because full previa almost always requires a cesarean delivery, while a low-lying placenta often allows for other options.
Why Most Cases Resolve on Their Own
The placenta doesn’t actually slide upward. What happens is that the lower part of the uterus stretches and grows significantly during the second and third trimesters, effectively pulling the placenta farther from the cervix. This process is sometimes called “placental migration,” though it’s really the uterine wall doing the moving.
The numbers are reassuring. Over 60% of low-lying placentas diagnosed in the second trimester have resolved by 26 weeks, and 88% have resolved by 30 weeks. Your care team will schedule a follow-up ultrasound, usually somewhere between 28 and 32 weeks, to check whether the placenta has moved into a safer position. If it hasn’t budged by then, you’ll likely have another scan closer to your due date to guide delivery planning.
Symptoms to Watch For
Many people with a low-lying placenta have no symptoms at all, and the diagnosis comes as a surprise on their anatomy scan. When symptoms do appear, the hallmark is painless vaginal bleeding, typically bright red. This can happen because the cervix begins to thin and stretch as pregnancy progresses, disturbing the nearby placental tissue. Any vaginal bleeding during pregnancy warrants a call to your provider, but painless bleeding in the second or third trimester is particularly characteristic of a low placenta.
Who’s More Likely to Have One
Several factors increase the chance of the placenta implanting low:
- Previous uterine surgery. A prior cesarean delivery, D&C, or fibroid removal leaves scarring that can influence where the placenta attaches.
- Multiple prior pregnancies. Each pregnancy slightly changes the uterine lining, making low implantation more likely in later pregnancies.
- Age 35 or older.
- Carrying multiples. Twins or triplets require a larger placenta, which is more likely to extend toward the cervix.
- Smoking or cocaine use.
- Uterine fibroids.
Activity and Lifestyle During Pregnancy
If your placenta is low-lying, your provider may recommend reducing physical activity, avoiding intercourse, and skipping heavy lifting until follow-up imaging confirms the placenta has moved. These precautions (often called “pelvic rest”) are meant to minimize anything that could irritate the cervix or provoke bleeding. Not every provider gives the same advice, so the specifics depend on how close the placenta is to the cervix and whether you’ve had any bleeding episodes.
Light walking and gentle daily movement are generally fine for most people, but high-impact exercise or anything involving deep squatting or abdominal strain is typically off the table until you get the all-clear.
What Happens at Delivery
If the placenta migrates away from the cervix by the third trimester, a normal vaginal delivery is the standard plan. But when a low-lying placenta persists, the delivery approach depends on exactly how close it remains.
Research published in Obstetrics & Gynecology found that when the gap between the placenta and cervix measured 11 to 20 mm, half of those who attempted vaginal delivery succeeded. When the distance was 10 mm or less, the vaginal delivery rate dropped to about 19%. Based on these findings, a trial of labor is generally considered reasonable when the placenta sits 11 to 20 mm from the cervix. Closer than that, a planned cesarean is more likely, though the risk of severe complications didn’t significantly increase either way.
Complications Worth Knowing About
The main concern with a low-lying placenta is heavier-than-normal bleeding after delivery (postpartum hemorrhage). Even when the placenta appears to have migrated to a normal position by the third trimester, the risk doesn’t fully disappear. A 2024 study found that people whose low-lying placenta resolved still had about three times the odds of significant postpartum bleeding (13.2%) compared to those who never had a low placenta (4.1%). They were also more likely to need additional medications to control bleeding and had higher rates of extended hospital stays beyond seven days.
This doesn’t mean every resolved case leads to problems. The large majority of deliveries go smoothly. But your birth team will be aware of your history and prepared to manage heavier bleeding if it occurs, which is one reason that follow-up imaging and clear documentation in your chart matter.
The Follow-Up Timeline
After a low-lying placenta is found at the 20-week scan, you can expect at least one additional ultrasound to track its position. Most providers schedule this around 28 to 32 weeks, since the data shows 88% of cases have resolved by 30 weeks. If the placenta is still low at that point, a final check around 36 weeks helps determine whether a vaginal birth is feasible or a cesarean should be planned.
The waiting period between scans can feel stressful, but the odds strongly favor resolution. For the small percentage of cases that persist, having a clear delivery plan in place well before your due date gives your care team the best chance of a safe outcome for you and your baby.