Everything You Ever Wanted to Know About the Placenta

You've probably heard the word "placenta" plenty of times since you found out you were expecting. But what is the placenta, exactly? And why does it matter so much?

This temporary organ is doing some seriously heavy lifting throughout your entire pregnancy—nourishing your baby, filtering out waste, producing hormones, and even passing along immune protection. It's basically your baby's life-support system, all wrapped up in a disc-shaped organ about the size of a dinner plate.

Here's everything you need to know about the placenta, from how it forms to what happens after it's delivered.

What is the placenta?

The placenta is a temporary organ that develops inside your uterus during pregnancy. It connects to your baby via the umbilical cord and attaches to the wall of your uterus. Think of the placenta as the ultimate go-between: It's the interface where your body and your baby's body exchange everything needed to support growth and development—without ever mixing your blood with theirs.

By the time your baby makes their debut, your placental will weigh about one pound and measure roughly 9 inches (20 centimeters) in diameter. It's made up of both maternal and fetal tissue, and its genetic makeup is identical to your baby's. Once your baby is born, the placenta's job is done—and you’ll deliver it shortly after.

What does the placenta do?

The placenta is often described as your baby's lungs, kidneys, and liver all rolled into one! Here's a quick rundown of its major roles:

• Delivering oxygen and nutrients: Your blood passes through the placenta, and oxygen, glucose, and nutrients are transferred to your baby through the umbilical cord. This is how your baby gets the fuel they need to grow.
• Removing waste: The placenta filters carbon dioxide and other waste products from your baby's blood, transferring them back to your bloodstream for your body to dispose of.
• Producing hormones: The placenta acts as an endocrine organ, churning out hormones that maintain your pregnancy, support fetal development, and prepare your body for labor and breastfeeding. These include progesterone, estrogen, and human placental lactogen.
• Providing immune protection: As you get closer to delivery, the placenta passes antibodies from your immune system to your baby, giving them a head start on immunity that lasts for several months after birth.
• Acting as a barrier: The placenta allows essential substances to pass through while keeping your blood and your baby's blood separate. It also works to filter out some harmful substances—though it's worth noting that not everything is blocked. Some medications, alcohol, and other substances can still cross the placenta, which is why it's important to discuss all medications with your healthcare provider during pregnancy.

How and where does the placenta form?

The placenta begins forming very early in pregnancy. After a fertilized egg (now called a blastocyst) implants in the lining of your uterus—about five to 10 days after fertilization—some of those rapidly dividing cells start developing into the placenta. The placenta is formed from some of these early dividing cells and functions as a life-support system throughout pregnancy.

The placenta is fully formed by about 18 to 20 weeks of pregnancy, though it continues to grow alongside your baby right up until delivery.

Where the placenta attaches depends entirely on where the fertilized egg implants—and that's not something you have any control over. Your healthcare provider will check on the placenta's position during your 20-week anatomy scan. There are several common positions, and all are considered normal…

Posterior Placenta

A posterior placenta attaches to the back wall of your uterus, closest to your spine. This is one of the most common placements. Because the placenta isn't between your belly and your baby, you may feel kicks and movements earlier and more intensely.

Anterior Placenta

An anterior placenta is positioned on the front wall of your uterus, nearest your abdomen. It's perfectly normal and doesn't affect how well the placenta works. The main thing you may notice is that it can take longer to feel your baby's movements—often not until after 20 weeks—because the placenta is cushioning those kicks. An anterior placenta can also make it slightly trickier to find your baby's heartbeat on a Doppler ultrasound.

Fundal Placenta

A fundal placenta sits at the top of your uterus, between the two fallopian tube openings. This is a common and generally favorable position, as it leaves the lower part of the uterus clear for delivery.

Lateral Placenta

A lateral placenta attaches to the right or left side of your uterus. Like the other positions, this is normal. Some research has looked at whether lateral placentation may affect blood supply (since the placenta may receive blood primarily from one uterine artery rather than both), but in most pregnancies, it's not a cause for concern.

It's worth knowing that the placenta can appear to "move" as your pregnancy progresses. It's not actually relocating—your uterus is expanding, and the placenta's attachment point can shift upward as the uterine walls stretch. Most placentas migrate to the top or side of the uterus by 32 weeks.

What are common placenta issues?

While most placentas do their job without a hitch, there are some conditions worth knowing about. If any of these come up during your pregnancy, your healthcare provider will work with you on a plan to keep you and your baby safe.

Placenta Previa

Placenta previa occurs when the placenta partially or completely covers the cervix—the opening of the uterus. In most pregnancies, the placenta attaches at the top or side of the uterus, but with previa, it's positioned low enough to block your baby's exit route.

Placenta previa affects roughly 1 in 200 pregnancies and is most commonly detected during a second-trimester ultrasound. The good news? Many cases found early in pregnancy resolve on their own as the uterus grows and the placenta shifts upward. If it persists into late pregnancy, a c-section is typically recommended to avoid serious bleeding during delivery.

The primary symptom is painless vaginal bleeding during the second half of pregnancy. Risk factors include a previous c-section, prior uterine surgery, being pregnant with multiples, and being over age 35.

Placenta Accreta

Placenta accreta is a condition where part or all of the placenta attaches too deeply into the wall of the uterus. Normally, the placenta detaches from the uterine wall after delivery—but with accreta, the blood vessels and other tissue grow into the muscle of the uterus and won't let go.

Placenta accreta exists on a spectrum. In its milder form (accreta), the placenta extends into the uterine muscle. In placenta increta, the tissue invades even deeper into the muscle layer. And in the most severe form—placenta percreta—the placenta grows through the uterine wall entirely and may reach adjacent organs like the bladder.

The biggest risk factor is a prior c-section, and the risk increases with each subsequent cesarean delivery. Placenta accreta can cause serious, sometimes life-threatening bleeding during delivery. Treatment often involves a planned c-section, and in some cases, a hysterectomy may be necessary.

Placental Abruption

Placental abruption occurs when the placenta partially or completely separates from the uterine wall before delivery. This is a serious complication because it can cut off your baby's supply of oxygen and nutrients and cause heavy bleeding for the pregnant person.

Abruption affects roughly 1 in 100 pregnancies and most commonly happens in the third trimester. Symptoms can include sudden abdominal or back pain and vaginal bleeding, though in some cases the blood can be trapped behind the placenta, meaning there may be no visible bleeding at all.

Risk factors include high blood pressure, a history of abruption in a previous pregnancy, abdominal trauma (such as from a car accident or fall), and substance use. The cause is often unknown, however. Treatment depends on the severity and how far along the pregnancy is—mild cases may be monitored closely, while more severe cases may require early delivery.

Placental Insufficiency

Placental insufficiency (sometimes called placental dysfunction) means the placenta isn't transferring blood, oxygen, and nutrients to your baby as efficiently as it should. This can lead to fetal growth restriction, low birth weight, or, in more serious cases, preterm birth.

Placental insufficiency affects about 1 in 10 pregnancies. It can be caused by a range of factors, including high blood pressure, diabetes, blood-clotting disorders, and smoking.

One tricky aspect of this condition is that there are often no noticeable symptoms for the pregnant person. Your healthcare provider may detect it when your uterus isn't growing as expected, or when an ultrasound shows your baby is measuring smaller than anticipated. While there's no cure, close monitoring and managing underlying health conditions can help—and in some cases, early delivery may be recommended.

Retained Placenta

A retained placenta is when the placenta isn't delivered within about 30 minutes after your baby is born. This can happen if the placenta gets trapped behind a partially closed cervix, if the uterus isn't contracting strongly enough to release it, or if the placenta is abnormally attached to the uterine wall.

Retained placenta occurs in roughly 1 to 3% of deliveries. Without treatment, it can lead to serious infection or life-threatening blood loss. Treatment may include medication (like oxytocin) to encourage contractions, or a manual removal procedure performed by your healthcare provider.

What are signs of issues with the placenta?

Many placental conditions are detected during routine prenatal care—which is one of many reasons keeping up with your prenatal appointments is so important. But there are some warning signs to be aware of:

• Vaginal bleeding: Any bleeding during the second or third trimester should be reported to your healthcare provider right away. It can be a sign of placenta previa, placental abruption, or other complications.
• Sudden abdominal or back pain: Sharp or constant pain—especially in the third trimester—could indicate placental abruption.
• Reduced fetal movement: If your baby is moving less than usual, it could be related to placental insufficiency or other concerns.
• Your uterus measuring small: If your healthcare provider notices that your belly isn't growing as expected, they may order additional testing to evaluate the placenta's function.
• Preterm contractions: Contractions before 37 weeks could sometimes be linked to placental issues.

If you notice any of these symptoms, contact your healthcare provider. In the case of heavy bleeding or severe pain, seek emergency care. Most placental problems can be managed effectively when caught early.

How is the placenta delivered?

The delivery of the placenta is known as the third stage of labor—and it happens right after your baby is born.

• During a vaginal birth: After your baby arrives, you'll continue to have mild contractions. Your healthcare provider may give you a shot of oxytocin (Pitocin) to help your uterus contract and minimize bleeding. They may also gently massage your lower abdomen to encourage the uterus to release the placenta. You might be asked to push one more time—and the placenta is typically delivered within five to 30 minutes of your baby's birth.
• During a c-section: Your healthcare provider removes the placenta from your uterus during the surgical procedure.

Either way, your provider will carefully examine the placenta after delivery to make sure it's intact. Any fragments left behind in the uterus could cause bleeding or infection and would need to be removed.

What happens to the placenta after birth?

Once the placenta is delivered and examined, the hospital typically disposes of it as medical waste. But in recent years, more parents have expressed interest in alternative practices. Here are some you may have heard about:

• Placenta encapsulation: This involves dehydrating the placenta and turning it into capsules. Proponents believe it can help with postpartum recovery, energy, and milk supply. However, there is currently no scientific evidence supporting these claims. The Centers for Disease Control and Prevention (CDC) published a case report in 2017 describing an infant who developed a serious bacterial infection potentially linked to contaminated placenta capsules. The CDC does not recommend placenta encapsulation.
• Burying the placenta: In many cultures around the world, the placenta is considered sacred, and burying it is a meaningful ritual to honor the bond between parent and child.
• Lotus birth: This is the practice of leaving the umbilical cord and placenta attached to the baby until the cord dries and naturally falls off (typically within three to 10 days). Major medical organizations, including ACOG, do not recommend this practice because once the placenta leaves the body, it's no longer circulating blood and can become a source of infection. ACOG does, however, support delayed cord clamping for 30 to 60 seconds after birth, which has been shown to benefit newborns.
• Pathology examination: In some cases—such as preterm birth, fetal growth restriction, or preeclampsia—your healthcare provider may send the placenta to a pathology lab for a closer look. This can provide valuable information about what happened during the pregnancy.

If you're interested in taking your placenta home or doing something specific with it, talk to your healthcare provider and hospital well ahead of your due date so you can make arrangements.

The Bottom Line on the Placenta

The placenta is one of the most impressive organs your body creates—a temporary powerhouse that nourishes, protects, and sustains your baby for the duration of pregnancy. While it quietly does its job in the background, understanding what it does and what can go wrong empowers you to have informed conversations with your healthcare provider and stay alert to any signs that something might be off.

The best thing you can do for your placenta (and your baby) is keep up with your prenatal appointments, avoid smoking and substance use, manage any chronic health conditions, and talk to your provider about your concerns.

More on Labor and Delivery:

• Early Signs of Labor
• C-Section Recovery Tips
• Dilation and Effacement
• What’s a Membrane Sweep?

Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.