What is placenta previa?
Placenta previa is when the placenta sits low in the uterus and partly or fully covers the cervix, the opening your baby would normally pass through during birth. Instead of attaching higher up on the uterine wall, it implants near or over that opening. This matters because the cervix needs to open during labor, and a placenta blocking that path can tear and bleed heavily as it does. It's identified most often on a routine ultrasound, sometimes before you've noticed anything unusual at all.
Finding out your placenta is low-lying can feel alarming, especially if you weren't expecting any complication. It helps to know that a low-lying placenta found in the second trimester is common, and that most of these move out of the way on their own as the pregnancy progresses and the uterus grows. Whether it resolves or persists is something your provider will track with follow-up scans rather than something you can predict from symptoms alone. Either way, being monitored doesn't mean something has already gone wrong.
What are the symptoms of placenta previa?
The hallmark symptom is painless vaginal bleeding, usually bright red, that can start suddenly in the second half of pregnancy without any warning. It may be light spotting one time and heavier the next, and it often stops on its own before starting again later. Some people have no bleeding at all before the diagnosis is made on ultrasound, so the absence of bleeding doesn't rule previa in or out. Because the bleeding is typically painless, it can be easy to dismiss as minor — it isn't something to wait out.
Call your provider the same day for any vaginal bleeding in the second half of pregnancy, even if it's light and stops quickly. Go to an emergency room or call emergency services for heavy bleeding, bleeding that soaks through a pad within an hour, dizziness, fainting, or contractions along with bleeding. Heavy bleeding from placenta previa can escalate quickly, and getting evaluated promptly is what keeps both you and your baby safe. It's always reasonable to be evaluated even if you're not certain the bleeding is significant.
What causes placenta previa, and who's at higher risk?
There's no single known cause of placenta previa — it comes down to where the fertilized egg happened to implant in the uterus. Certain factors make it somewhat more likely, including having had previous cesarean deliveries, prior uterine surgery, a previous placenta previa, or being pregnant with twins or more. Smoking and becoming pregnant at an older age are also linked with a higher chance, as is a history of many previous pregnancies. Each additional cesarean scar adds a bit more risk in future pregnancies, which is one reason providers weigh delivery decisions carefully when previa is a possibility down the line.
It's worth being clear that many people diagnosed with placenta previa have none of these risk factors, and having one or more of them doesn't mean it will happen. These are patterns seen across large groups of pregnancies, not predictions for any individual one. If you've been told you have a low-lying placenta or previa, it isn't the result of anything you did during this pregnancy. The placenta's position is set very early on, generally before you'd have had any way to influence it.
How is placenta previa diagnosed?
Placenta previa is diagnosed by ultrasound, usually first spotted at the routine second-trimester anatomy scan around 18 to 22 weeks. If the placenta is found to be low-lying or covering the cervix at that point, your provider will schedule a follow-up ultrasound later in pregnancy, often in the third trimester, to see whether it has moved. A transvaginal ultrasound — done with a probe rather than over the abdomen — gives a clearer, more reliable view of exactly how the placenta relates to the cervix than an abdominal scan alone. It's a standard, low-risk part of confirming or ruling out previa, not a sign of extra concern on its own.
Between scans, your provider may also ask you to watch for and report any bleeding, and may space out visits more closely if you're further along and previa hasn't yet resolved. If the placenta still covers or comes close to the cervix later in the third trimester, it's less likely to move further before delivery. That finding shapes the delivery plan going forward, so your care team will talk you through exactly what it means for your specific situation rather than leave you guessing from the ultrasound report alone.
How is placenta previa managed during pregnancy?
Management depends mostly on whether you're having any bleeding and how far along you are. If there's no bleeding and the previa is picked up incidentally, care usually involves extra ultrasounds to track the placenta's position, along with guidance to avoid things that could trigger bleeding — often including pelvic rest, meaning no intercourse and nothing placed in the vagina, and avoiding strenuous exercise. If bleeding does occur, treatment depends on how much, how far along you are, and how you and your baby are doing on monitoring, and can range from rest and close observation to hospital admission for closer watching.
In cases of heavy or repeated bleeding, especially earlier in pregnancy, your provider may recommend a hospital stay so you can be monitored continuously, with steroid injections sometimes given to help your baby's lungs mature in case an early delivery becomes necessary. This kind of monitoring can feel like a lot, particularly if you were feeling fine otherwise. It's a precaution built around the fact that previa bleeding can become unpredictable quickly, not an indication that a serious complication is definitely coming.
What does placenta previa mean for delivery?
Placenta previa that persists into the third trimester means a cesarean delivery, since a placenta covering the cervix makes vaginal birth unsafe for both you and your baby. If previa is still present close to term, delivery is typically planned, often somewhere around 36 to 37 weeks, earlier than a standard due date, to reduce the chance of a sudden bleeding emergency before a scheduled birth. The exact timing depends on your bleeding history, how the placenta looks on your most recent scan, and how you and your baby are doing overall.
If you've had heavy bleeding or the previa is complicated by the placenta growing too deeply into the uterine wall — a related condition your provider would flag separately — delivery may need to happen even sooner, at a hospital equipped to manage significant blood loss. This can mean a very different birth experience than you may have pictured, and it's fair to grieve that even while focusing on a safe outcome. Talk with your provider well before your due date about exactly what your delivery plan looks like, including what happens if bleeding starts before that date arrives.