What Are the Different Parts of the Placenta?

By the time you find out you're pregnant, your body is already busy growing a new organ. While not a permanent part of your body, the placenta is considered an organ and is a vital part of pregnancy. It is formed during the first three months and grows parallel to the uterus in the fourth month. The development of the placenta is critical for a successful pregnancy. There are many different parts that make up the placenta and each has its own purpose.

What Is a Placenta?

The placenta attaches to the wall of the uterus during pregnancy. It provides vital nutrients and oxygen to your baby through the umbilical cord.

There are two sides to the placenta: the fetal side (known as chorion) and the maternal side (known as decidua). The average placenta weighs around one pound, is about 20 centimeters in diameter, and is about three centimeters thick. If you have twins or multiples, there may be one large placenta that the twins share, or separate placentas, one for each baby.

Attached to the placenta will be the umbilical cord. The umbilical cord is usually around 50 to 60 centimeters long.

The Parts of the Placenta

Fetal Side (Chorion)

The fetal side of the placenta faces in, toward the fetus. It has a shiny appearance with the umbilical cord attached in the center, with visible veins branching out.

Amnion

The amnion is the membrane that covers the fetal side of the placenta. It helps protect the fetus and regulates temperature. You may be more familiar with the term amniotic fluid, which is secreted from the membrane. The fetus breathes amniotic fluid and it also cushions the fetus from the walls of the uterus.

Maternal Side (Decidua)

The maternal side of the placenta faces out, toward the mother. This side of the placenta is a dark maroon, reddish color. When a person is not pregnant, it is known as the endometrial lining of the uterus. It also contains lobules known as cotyledons.

During a placental exam, a doctor looks for any gaps or missing cotyledons, which can indicate possible retained placenta.

Sometimes, sections of the placenta have a white-like tone and are slightly hardened to the touch when compared to the normal sections of the placenta. These are known as calcifications and are one of the most commonly seen placental abnormalities.

“This is often seen when one is closer to 41 or 42 weeks of pregnancy, as it's a sign the placenta is older and has peaked in terms of its function,” explains Jennifer Lincoln, MD, a board-certified OB/GYN in Portland, Oregon and author of "Let’s Talk About Down There: An OB-GYN Answers All Your Burning Questions without Making You Feel Embarrassed for Asking."

“We can also see this earlier in pregnancy in people who are smokers," Dr. Lincoln adds. "A calcified placenta doesn't work as well.” She notes this usually doesn’t affect the baby, but sometimes, it can lead to intrauterine growth restriction.

The Umbilical Cord

The umbilical cord should contain three blood vessels: two arteries and one vein.

The arteries are smaller in diameter, while the vein is much wider. The vein brings blood from the placenta to the fetus, while the umbilical arteries carry blood back from the fetus to the placenta. These vessels are surrounded by a gelatinous substance known as wharton’s jelly.

The cord is typically about two to three cm in width and between 50 and 60 cm in length. It develops from the fetal side of the placenta to the belly of the fetus, eventually becoming the baby's belly button.

What Happens to the Placenta After Birth?

Once your baby comes into the world, and you've delivered the placenta, your doctor will want to inspect it to make sure it's healthy. This process is called a placental exam.

What Is a Placental Exam?

The placental exam occurs after delivery of the placenta, which is the third and final stage of labor. When people think about labor and delivery, they focus on the baby, and they may forget that the placenta also needs to be delivered.

“The good news is delivering your placenta is a lot easier than birthing your baby, because placentas don't have a head or shoulders!” explains Dr. Lincoln. Delivery of the placenta usually occurs over a few minutes, but can take up to a half an hour.

“If you have an epidural, all you may feel is some pressure as the placenta delivers, or [you may feel] nothing at all. Without an epidural, it may feel a bit more intense, but again it's much easier than pushing a baby out!” Dr. Lincoln says.

Once the placenta is delivered, the placental exam can take place. Since the placenta is no longer in your body, the exam is completely painless for you and your baby.

While the placental exam is quick and doesn’t need to involve you, you can ask to see your placenta. Your doctor can explain to you the various sections and parts of the placenta.

“Don't be afraid to ask to see yours after your birth, and take photos [if you want],” suggests Dr. Lincoln. “They really are beautiful!” 

After a Placental Exam

If your healthcare provider suspects that part of the placenta is missing, or is concerned that placental tissue remains inside your uterus, action may need to be taken to remedy this problem. Retained placental tissue can lead to postpartum infection, problems with low breast milk supply, and postpartum hemorrhage.

Changing positions, breastfeeding your newborn, or receiving medication that stimulates uterine contractions are all possible ways to expel retained placenta. However, sometimes the tissue needs to be removed manually.

“We can either use our hand or a surgical instrument to swipe out the retained placenta,” explained Dr. Lincoln. “If someone has an epidural, this is often all that is needed for anesthesia, but we can also use sedating medications.” 

If there were any complications at the birth or potential issues with the baby, or the placenta has traits that are of concern, your provider may choose to send a portion or the entire placenta to a pathology lab for a more detailed evaluation.  

“A pathologist can analyze the placenta as a whole as well as on the microscopic level,” says Dr. Lincoln. “If needed, blood samples can also be sent from the placenta, which is sometimes done to look for genetic issues or infection.” 

Some abnormalities will indicate referral to a neonatologist or other pediatric specialist to evaluate your newborn. For example, if the umbilical cord only has one artery, instead of two, this may indicate rare congenital conditions that warrant further examination of your newborn.

If the placenta exam uncovers signs of infection, your doctor may prescribe antibiotics for you or your baby.

However, much of the time, the placenta is found to be completely normal. Or, the findings are incidental—meaning that they may not be “normal” but they don’t indicate a problem with the mother or baby.

As long as the placenta doesn’t need to be sent to pathology, it is usually disposed of with biohazard waste after the examination.

Taking the Placenta Home

If you intend to keep your placenta, it’s best to speak to your provider and the hospital or birthing center before your delivery day. This way, you can find out what the process is for those who wish to take home their placenta. You will know what forms (if any) you’ll need to fill out, and what supplies they require to transport your placenta home with you.

A Word From Verywell

The placenta is a very delicate and important organ in the development of your fetus. Its various parts work together to protect the fetus and bring it critical nutrients.

Delivering the placenta is known as the third stage of labor. Your body created that placenta, so don’t be embarrassed to ask to see it if you wish.

A placental exam is also often done after delivery. Remember that the vast majority of the time, the placental exam doesn’t find anything of concern. There are, however, times when the placenta reveals a potential health issue for the parent or baby. When something isn’t quite right, ask your OB/GYN or healthcare provider to explain what the next steps may be for you and your baby.