When Does the Placenta Form? Your Expert Guide

Pregnancy is wild—your body is wild.

From as early as six days after conception, there’s a flurry of complex changes and activity going on.

Cells dividing, hormones triggering, and the first signs of a brand new (temporary) organ. 🤯

Yep, growing right alongside your baby is the placenta—an impressive fusion of fetal and maternal tissue keeping your baby in tip-top shape until their debut.

If you want an easy way to define placenta, consider it your baby’s lifeline until they’re safe in your hands. 🙌

Great! So, how does it work?

And what exactly is the function of the placenta?

And when does the placenta form?

We tackle everything you need to know about this ingenious little organ, including position, complications, and delivery.

In this article: 📝

What is the placenta?

Simply put, the placenta is a disc-shaped organ that forms in your uterus during pregnancy.

Also called an afterbirth, this temporary organ aids the growth and development of your baby by giving them the oxygen and nutrients they need.

All while removing waste products from their system.

It’s probably one of the most important organs of your body and a true multi-tasker.

It’s lungs, liver, kidneys, gut, and endocrine glands rolled into one with the ability to supply your growing baby with everything they need while boosting your maternal metabolism to keep up the good work in later pregnancy.

No wonder the placenta is considered sacred in certain cultures!

How you define placenta depends on your view of this transient super-organ and the context you become acquainted with it.

One person’s medical waste is another’s spiritual symbol.

What week does the placenta attach?

The placenta starts to develop pretty soon after conception—although it doesn’t attach to the walls of your uterus until a bit later (more on that below).

Once a fertilized egg reaches your uterus from the fallopian tube, it has already transformed into a little cluster of dividing cells called a blastocyst.

The blastocyst stays in your uterus for a few days before attaching to the inner lining of your uterine wall (endometrium) in a move you know as implantation.

It continues to make new cells, separating them into layers.

Those on the outside will soon become the fetus, while the inner cells implant even deeper into the endometrium to become the placenta.

All this happens within the first six to 12 days of pregnancy.

Isn’t your body incredible?!

Can the placenta attach anywhere?

In short, yes.

The placenta attaches wherever your fertilized egg implants and, depending on where, could possibly cause some concerns.

Let’s look at each possibility:

• Posterior placenta: This is when the placenta attaches to the wall of your uterus near your spine. While it has been linked to pre-term labor, the posterior placenta is considered one of the better locations and one of the most common.
  
• Anterior placenta: An anterior placenta is when it attaches to the front wall of your womb—close to your belly. This is another common position and not typically a concern though it may make it harder to recognize when your baby kicks.
  
• Fundal placenta: This is when the placenta attaches to the top of the uterus. It may not start here but could move there to make room for vaginal delivery. It’s generally considered normal, though, and not majorly associated with any pregnancy complications.
  
• Lateral placenta: This is when the placenta has attached to the left or right side of the uterus. Less common than the posterior or anterior positions, one study suggests that women with a lateral placenta have a higher risk of preterm birth and preeclampsia.
  
• Low-lying placenta: Also known as (placenta previa). This is a pregnancy complication where the placenta partially or fully covers the cervix. Because of this, the low-lying placenta does carry extra risks and might mean you’ll need to have a cesarean section.

How do you know where your placenta is attached?

Your healthcare provider will be able to see the position of your placenta during an anatomy scan at week 20.

This marks the halfway point of your pregnancy and is an opportune time for your medical team to see how your baby is developing.

Alongside the position of the placenta, the technician will also be checking for genetic conditions and organ abnormalities.

If your placenta is low-lying or is any cause for concern, you’ll be offered an extra ultrasound for week 32.

This is because the placenta can move again as your uterus grows but tends to settle down by this point.

From here, your medical provider will be able to help you plan the safest course of action for your birth plan.

When does the placenta form?

So, what starts as just a few cells in the first four weeks of pregnancy eventually grow to be several inches long.

But this is no overnight success story.

During the first ten weeks of pregnancy, the placenta continues to develop, all the while producing and releasing human chronic gonadotropin (hCG).

This stellar move triggers your body to release more estrogen and progesterone, thickening your uterine lining, halting menstruation, and just all around supporting your pregnancy.

And yes, it’s also the hormone that tips off pregnancy tests that your whole world is about to change.

When is the placenta fully formed?

While the placenta continues to develop throughout your term—eventually reaching a weight of about a pound—by 12 weeks of pregnancy, the placenta has all it needs to support your baby.

By week 20, the placenta is fully formed, and by 34 weeks, it is considered mature.

Shortly after your baby is born, your uterus will continue to contract, helping the placenta separate from the uterine so you can deliver it.

When does the placenta take over?

As your placenta develops, the corpus luteum serves as the main source of hormones and nourishment during the first trimester.

Wait, isn’t that a cyst?

Well, yes, albeit a perfectly normal, harmless one that forms after your ovaries release an egg every month.

Once the egg gets fertilized, the corpus luteum acts as a temporary organ, releasing the progesterone needed to turn your uterus into a healthy, nourishing space for your fetus to grow.

Around week 12, the placenta takes over, producing enough progesterone for the corpus luteum to take its leave and slowly break down.

Keep in mind forming this powerhouse organ is no easy feat for you either.

Just as the corpus luteum is taken on the heavy lifting until the placenta gets up to speed, so too are your energy levels (hello pregnancy fatigue).

Once the second trimester arrives, the placenta is in the driving seat.

From here, it takes water, oxygen, and nutrients directly from your bloodstream as it flows through your uterus, delivering them to your baby via the umbilical cord.

And in an expert exchange, the placenta filters back out carbon dioxide and unwanted waste your baby doesn’t need.

The placenta also does another important job: preventing harmful things from reaching your baby.

It works hard to keep viruses and bacteria out of the womb and stops the baby’s cells from transferring back into the mother’s blood.

Once you get closer to your due date, it passes through antibodies to your baby, jumpstarting their immune system for those first few months of life.

Impressive, no?

Just you wait.

What happens to the placenta in multiple births?

Do multiple babies mean multiple placentas? Or do the babies share one placenta?

Well, the answer is yes and yes…

Depending on the type of twins you’re carrying, it is possible for the babies to share a placenta.

This can happen in the case of identical twins when the placenta forms before the embryo split into two or more babies).

Otherwise, if the babies are non-identical (also known as fraternal twinsl), then each baby will have their own placenta.

Again, this is something that can be seen on ultrasounds, so your healthcare provider will discuss it with you if you ask.

Delivery of the placenta: does it hurt?

Just as the placenta grows alongside your baby, so too does it leave once you’ve given birth.

Its watch has ended, so to speak.

With your baby in the safety of your (more than capable) hands, there’s no more duties for the placenta to fulfill, and so, the third stage of labor begins.

If you’ve had a vaginal birth, the placenta is typically delivered between five and thirty minutes after your baby.

During this stage, you’ll continue to experience contractions, but these will be far less intense.

You may even feel the urge to push, or your healthcare provider may help the afterbirth along by massaging your uterus.

If you’ve had a C-section, the placenta will be removed through the same incision used to deliver your baby

As for what happens to the placenta after birth, that entirely depends on the setting.

Most hospitals treat the placenta as medical waste and simply dispose of it.

But it’s not uncommon now for parents to keep this little lifeline—to honor it with a burial or even eat it by way of placenta encapsulation.

That being said, there’s nothing stopping you from honoring this dedicated worker from a distance.

What matters is that it’s done its duty well.

The rest is up to you, mama.

You’ve got this! ❤️