A low placenta means the placenta has attached in the lower part of your uterus, close to or covering the cervix. This is common to see on a mid-pregnancy ultrasound, affecting roughly 11 percent of patients scanned around 20 weeks. The good news: about 95 percent of these cases resolve on their own as the uterus grows and the placenta effectively moves upward. For the small number that persist, careful planning ensures the safest possible delivery.
Low-Lying Placenta vs. Placenta Previa
These terms describe different degrees of the same problem, and the distinction matters. A “low-lying placenta” means the lower edge of the placenta sits within 20 millimeters (about 2 centimeters) of the cervical opening but doesn’t cover it. “Placenta previa” means the placenta actually overlaps or completely covers the cervical opening. Both are measured on ultrasound, and the distance in millimeters between the placenta’s edge and the cervix determines which category you fall into.
Older terminology split things further into partial, marginal, and complete previa. Current practice simplifies this: either the placenta covers the cervix (previa) or it’s close but not covering it (low-lying). By the time of delivery, true placenta previa occurs in about 4 to 5 out of every 1,000 births.
Why Most Low Placentas Move Up
The placenta doesn’t literally detach and migrate. What happens is the lower part of the uterus stretches and grows significantly during the second and third trimesters. As this segment elongates, the placenta is carried upward and away from the cervix. This process is sometimes called “placental migration,” and it’s remarkably reliable.
In a large prospective study, only 5 percent of placentas that were low in the second trimester remained low in the third trimester. Your care team will typically schedule a follow-up ultrasound after 28 weeks, with most re-checks happening around 31 to 32 weeks, to see whether the placenta has moved to a safe position. If it hasn’t budged by then, additional scans will track it closer to your due date.
What a Persistent Low Placenta Means for You
If the placenta stays low or remains over the cervix into the third trimester, the primary concern is bleeding. Because the cervix begins to thin and open as your body prepares for labor, a placenta sitting over or near that area can partially separate, exposing blood vessels. The hallmark warning sign is bright red vaginal bleeding, typically painless, after 20 weeks. Sometimes it occurs alongside contractions that cause cramping, but painless bleeding is more characteristic.
Bleeding from a low placenta can range from light spotting to heavy hemorrhage. Any vaginal bleeding in the second or third trimester warrants an immediate call to your provider. Heavy bleeding requires emergency care.
Preterm Birth
Persistent placenta previa raises the chance of delivering early. About 5 percent of all preterm births are attributed to placenta previa, and the risk climbs if you experience bleeding episodes during pregnancy. Antepartum bleeding is one of the strongest predictors of preterm delivery in these cases. If your provider is concerned about early delivery, you may receive steroid injections to help your baby’s lungs mature faster, typically given between 24 and 34 weeks.
Placenta Accreta Spectrum
When the placenta implants low, especially in a uterus with a scar from a previous cesarean section, there’s an increased chance of the placenta growing too deeply into the uterine wall. This group of conditions, called placenta accreta spectrum, means the placenta may not separate normally after birth. The risk factors overlap significantly: prior cesarean delivery, previous uterine surgery, and placenta previa. Your care team will look for signs of abnormal attachment on ultrasound if you have these risk factors.
Vasa Previa
A low-lying placenta is also a risk factor for vasa previa, a condition where fetal blood vessels run across the membranes covering the cervix, unprotected by placental tissue. This is uncommon but serious, because those exposed vessels can rupture during labor. Most cases of vasa previa are actually caught during routine follow-up ultrasounds for low placenta. Transvaginal ultrasound with color Doppler is highly accurate for detecting it, with one large study of nearly 34,000 women finding 100 percent sensitivity when screening was done in the second trimester.
Activity Restrictions During Pregnancy
If your placenta is near or partially covering the cervix, your provider will likely recommend changes to your daily routine, especially if you’ve had any bleeding. The goal is to avoid anything that could trigger contractions or disturb the placenta.
- Physical activity: Running, jumping, heavy lifting, squatting, and strenuous exercise are typically restricted. Light walking is usually fine, but confirm with your provider.
- Sexual intercourse: Most providers advise against intercourse when there’s a low placenta or previa, since it can cause contractions or irritate the cervix.
- Vaginal insertions: Tampons, douching, and anything inserted vaginally should be avoided.
- Rest: Some providers recommend modified bed rest at home, particularly after a bleeding episode.
These restrictions feel frustrating, especially when you feel fine. They’re precautionary, and they may be loosened if a later scan shows the placenta has moved to a safe distance.
How Delivery Is Planned
The distance between the placenta’s edge and the cervical opening at your final ultrasound drives the delivery plan. If the placenta completely covers the cervix, a cesarean section is necessary because the baby cannot pass through without causing dangerous bleeding. This is non-negotiable for true placenta previa and is typically scheduled around 36 to 37 weeks.
For a low-lying placenta that’s close but not covering the cervix, the picture is more nuanced. Research comparing planned vaginal delivery with elective cesarean in women with low-lying placentas found that when the placenta’s edge was 11 to 20 mm from the cervix, half of women who attempted vaginal birth delivered successfully. When the distance was 10 mm or less, only about 19 percent achieved a vaginal delivery, though attempting labor at that distance did not increase the rate of severe bleeding or serious complications. Your provider will weigh the exact measurements, your bleeding history, and your preferences when discussing options.
What to Watch For
The most important thing you can do between now and delivery is recognize bleeding early. Bright red vaginal blood, with or without pain, is the signal that something needs attention. Some women experience a small initial bleed that stops on its own, sometimes called a “sentinel bleed,” followed weeks later by more significant episodes. Not every case involves bleeding at all, but knowing what to look for keeps you prepared.
Between ultrasounds, there’s nothing you did to cause the placenta to implant low, and there’s nothing specific you can do to make it move. The uterus handles that on its own in the vast majority of cases. Your role is to follow activity guidelines, attend your follow-up scans, and get prompt care if bleeding occurs.