What Is Placenta Previa?

"Placenta low-lying" or "placenta covering the cervix" — if either phrase has appeared on your scan report, placenta previa is the name behind it. The 27-second video at the top of this page gives the quickest possible picture: where the placenta normally sits, and what changes when it lies low instead. The questions below are the ones that usually come next.

First, what exactly is lying where?

The placenta is the organ that grows inside the uterus during pregnancy and passes oxygen and nourishment to the baby. In most pregnancies it attaches high up, well away from the cervix — the opening at the bottom of the uterus that the baby passes through at birth. In placenta previa, it attaches low down instead, lying close to the cervix, partly over it, or completely covering it. That position matters for one straightforward reason: if the placenta sits across the exit, it is in the way when labour begins, and the tissue there can bleed as the cervix starts to change late in pregnancy.

How would you even know it is there?

Often, the first anyone knows is the routine ultrasound scan, where the sonographer notes where the placenta is lying as a standard part of the check — our overview of ultrasound in pregnancy explains what those scans look at. A low placenta seen earlier in pregnancy is not always the final picture, because as the uterus grows, the placenta can appear to shift upwards relative to the cervix. That is why a follow-up scan later in pregnancy is commonly arranged: to see whether it has moved clear or whether it is still covering the cervix as the due date approaches. Some people also experience painless bleeding in the second half of pregnancy, which is one of the recognised signs and a reason to contact your maternity team promptly, even if it stops.

So what changes for the rest of the pregnancy?

Mainly, the level of watching. You can expect extra scans to track the placenta's position, and your team may talk with you about taking certain activities more gently — their advice will be tailored to how much of the cervix is covered and whether there has been any bleeding, so their guidance comes first. Nothing you did causes this; it is about where the placenta happened to implant, not about anything you ate, lifted, or did before you knew.

And what does it mean for the birth itself?

If the placenta is still covering the cervix near the end of pregnancy, a vaginal birth would mean the baby trying to pass an opening that is blocked, so a planned caesarean birth is usually recommended in that situation — our comparison of C-section and vaginal delivery walks through how the two differ. If follow-up scans show the placenta has moved clear, the plan can change again. Either way, the plan is made from your own scan pictures, not from general articles — which is exactly how it should be.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about placenta previa, not medical advice. Any bleeding in pregnancy should be reported to your own maternity team promptly, and decisions about monitoring and birth planning belong with the clinicians who have seen your scans.

Frequently Asked Questions

Does a low placenta early in pregnancy always mean placenta previa at birth?
No. A placenta that looks low on an earlier scan can appear to move away from the cervix as the uterus grows. That is why a later follow-up scan is used to confirm the position before birth plans are finalised.

What is the main warning sign to act on?
Bleeding in the second half of pregnancy — classically without pain — is the sign most associated with placenta previa. Do not wait to see whether it happens again; contact your maternity team straight away.

Can placenta previa be prevented?
There is no step you can take before or during pregnancy that guarantees where the placenta implants. It is a matter of where implantation happened, not something caused by your actions.