What Is a Posterior Placenta?

Posterior placenta is one position of the placenta. Here’s everything you need to know about how it impacts pregnancy and delivery.

Medically reviewed by Andrea Chisholm, MD FACOG

The placenta is considered the baby’s lifeline, so it’s little wonder close medical attention is paid to this vital organ. During pregnancy, the placenta provides nutrients and oxygen from your body to your fetus via the umbilical cord.

But did you know the position of the placenta can reveal critical insights into the health of your pregnancy? Many pregnant people will be told they have a posterior placenta, but what does this mean for you and your fetus?

Posterior placentas are common, but given the importance of placement, it’s helpful to know how this may affect your pregnancy. Experts weigh in on all you need to know.

Related: What to Know About the Placenta During Pregnancy

What Does Posterior Placenta Mean?

Shortly after conception, the placenta attaches itself within the uterus in one of four main positions. One of the locations is posterior, which simply means the placenta has implanted on the back of your uterus, closest to your spine. Generally speaking, a posterior placenta won’t negatively impact your pregnancy and it’s unlikely to complicate labor or delivery.

“Posterior placenta is for the most part a normal variation and of little to no clinical consequence,” explains Robert M. Silver, MD, a professor of obstetrics and gynecology at the University of Utah Health Sciences Center.

Other placental positions include:

• Anterior: at the front of your uterus, closest to your abdomen

• Fundal: at the top of your uterus

• Lateral: on the left or right side of your uterus

• Low-lying: located toward the bottom of your uterus, potentially obstructing the cervix

What To Know About the Placenta

The placenta is a temporary organ created to support your fetus during pregnancy. Along with providing nutrients and oxygen to your little one, the placenta removes waste and carbon dioxide while producing the necessary hormones to help your fetus grow.

How Does Posterior Placenta Affect Delivery?

A posterior placenta is normal and both vaginal and C-section births are usually considered safe in this scenario.

There are no major medical concerns or risks with a posterior placenta by itself, explains Karin A. Fox, MD, MEd, FACOG, FAIUM, an associate professor, fellowship director, and clinical director of Baylor College of Medicine's Maternal-Fetal Medicine Division.

“We get more concerned if the placenta is low-lying or ‘previa,’ where the placenta covers the inner portion of the cervix," she says. If you have placenta previa, a C-section is usually recommended–whether posterior or otherwise. However, the edge of the placenta can move safely away from the cervix later in pregnancy and reduce any risks.

How Do I Know I Have a Posterior Placenta?

Your sonographer will be able to tell you the location of your placenta at your anatomy scan, usually between 18-22 weeks. For many, this might be the only time you hear about the position of your placenta, unless it’s combined with other factors.

Can There Be Posterior Placenta Complications?

While having a posterior placenta is unlikely to pose any risks to you or the fetus itself, there are some conditions where knowing the exact location of your placenta will be crucial. This is why sonographers carefully study the position of the placenta when you get your routine scans.

One serious medical condition that may affect the placenta wherever it’s implanted is placenta accreta spectrum, an area Dr. Fox is well versed in as the lead of Baylor College of Medicine’s placenta accreta spectrum care team. When this happens, the placenta doesn’t spontaneously detach after the baby is delivered and, in severe cases, can lead to life-threatening bleeding. Although it is most common when the placenta is low, anterior, and in the region of a uterine scar from a prior surgical procedure, those with posterior placentas can also be affected.

“When a placenta is posterior and placenta accreta is present, it can be more difficult to identify on ultrasound because it is more difficult to see the entire placenta with the baby in front of it,” explains Dr. Fox. “For this reason, anyone who has risk factors for placenta accreta spectrum should have their sonogram performed by experts and may require delivery in a referral center with a specialized team.”

Dr. Silver agrees that occasionally a posterior placenta can make prenatal diagnosis of placental problems slightly more challenging. But he says most of these conditions can still be reliably diagnosed using transvaginal ultrasound, if necessary.

Related: What Is an Anterior Placenta?

What Are Posterior Placenta Benefits?

Pregnant people with posterior placentas may enjoy some benefits that others with placentas in different positions won’t.

“Some people report that they are more able to feel baby's movements and kicks when the placenta is posterior because there is just a bit less between baby and mom's abdomen when the placenta is behind the baby,” says Dr. Fox.

Posterior placenta can also make it easier to perform an external cephalic version, or a procedure to turn the baby from breech to ‘head down’ to allow for a vaginal delivery.

Plus, posterior placenta may slightly increase the success and decrease the risk of certain procedures, explains Dr. Silver. “In cases of placenta previa or low-lying placenta, the cesarean delivery is slightly easier and prone to less blood loss if the placenta is posterior. However, these benefits are minor and uncommon,” he says.

While one study shows posterior placentas could be associated with preterm labor, others suggest that it’s less risky overall compared to other placental positions. For example, a study found posterior placentas result in less adverse pregnancy, delivery, and infant outcomes than fundal and lateral locations. Meanwhile another study investigating prenatal hemorrhage in patients with placenta previa cited anterior positions–not posterior–as a notable risk factor.

Can a Posterior Placenta Indicate the Baby’s Sex?

Some studies have tried to find evidence between the location of the placenta and sex. Generally, these reports are disputed with one study suggesting there is no correlation at all. The best way to discover the sex of your baby is by ultrasound.

When To Seek Medical Help

Physical symptoms are unlikely to indicate where your placenta is located and whether there is anything wrong. Instead, any symptoms relating to your placenta are likely to be more general, such as vaginal bleeding or pain, and these should always be investigated.

“Vaginal bleeding may be associated with placental problems–regardless of whether it is posterior, anterior, fundal, or lateral–and should prompt contact with a medical provider,” advises Dr. Silver.

The Bottom Line

Without any physical symptoms or suspicions on an ultrasound, it’s safe to assume that your posterior placenta is a variation of normal and unlikely to cause you any trouble. But if you have any concerns regarding fetal movement or if any abdominal pain, bleeding, or severe back pain is present, contact your health care provider.

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