Everything We Know About the Placenta

Emily Oster:

A lot of us totally forget that we even had a placenta or delivered it because when the placenta comes out, you’re sitting with a little baby on your chest, and it’s easy, relatively speaking, to push out the placenta.  But that last little push when you’re holding your baby says goodbye to a truly amazing organ — to a couch cushion, your baby’s first bodyguard, its waterbed. It’s your baby’s first friend. We’re going to finally give the placenta its due.  Let’s set the stage by just explaining what the placenta is.

Dr. Gillian Goddard:

The placenta is an organ. It does many different things, but I think at the most basic level, it allows communication between the fetus and the mother so that the fetus can get the things that it needs to grow and develop appropriately. When the placenta implants in the side of the uterus, there are multiple cells at this point in the embryo. The very earliest things that happen are some differentiation of some different types or groups of cells in that little clump of cells that is a very, very early pregnancy.  One set of those groups of cells actually grows into the placenta, and it tells the uterine lining to change so that the uterine lining interfaces with the cells that grow into the placenta. If you’ve ever had something called chorionic villus sampling, which is one of the tests that we do for genetic testing, they’re actually testing the villi, which are the little pieces of baby DNA that are interfacing with the lining of the uterus to communicate with one another.  In some ways, the placenta is the only organ that’s made up of two people together, which I just love.

Emily Oster:

The way the placenta works is it’s attached to the wall of the uterus and it’s between the wall of the uterus and the baby.

Dr. Gillian Goddard:

Yes, it’s like a couch cushion that sits between the wall of the uterus and the baby, but it’s physically attached to the wall of the uterus.

Emily Oster:

Why do we need the placenta? Why not just connect directly to the baby, which seems more efficient?

Dr. Gillian Goddard:

The placenta does more than connect mom and baby. It is a barrier that can keep some things from mom away from the baby. Some types of things that mom might experience, types of illnesses and things, can’t cross the placenta. In that way, it’s protective for the baby. 

Emily Oster:

I am imagining the baby has grown this extra organ, which bosses mom’s body to do things that the baby needs. Is it responsive in that sense? Is there a sense in which if the baby needs more, it uses the placenta to get more from mom?

Dr. Gillian Goddard:

It’s less responsive than that. It sets up this entire ecosystem almost inside of mom’s body that supports the baby, but it tends to make more of things and not necessarily to turn things up and down. 

Emily Oster:

Do we have any idea why this is an efficient way to do this?

Dr. Gillian Goddard:

I don’t know that we know exactly why. Some of this is that mammals are much more complex and so they need more nutrients in order to grow and develop during pregnancy because you’re developing a much more complex creature with a more complex brain and more complex types of physiology. Mammals are warm-blooded, so there’s all kinds of maintaining body temperature that have to develop as part of being a healthy mammal to function in the world. This system allows you to grow a more complex thing, animal or person.

Emily Oster:

Let’s talk about what can go right or wrong with the placenta. Let me frame the question in a way that I think many people would ask: What can I do to get the best placenta? What things could I do to make my placenta really like a nice cushion with a good-quality upholstery, stain-resistant? What’s it going to take?

Dr. Gillian Goddard:

The biggest thing that you need to grow a placenta is a healthy embryo, which you only have so much control over. Remember, this isn’t like, I want to give my baby a super-high IQ. We’re talking about just creating, quite frankly, a temporary organ. You need a healthy embryo and you need lots of energy. That is why the beginning of pregnancy can make people feel really tired, because it requires a lot from the mother’s body to undergo this big physiologic change to support the baby. The biggest thing you can do is listen to that and rest as much as you can.

Emily Oster:

Sometimes people get told they have either an anterior or posterior placenta. What does that mean?

Dr. Gillian Goddard:

It literally refers to the location on the wall of the uterus where the placenta has grown. So when that little embryo, that clump of cells, comes floating into your uterus from the fallopian tube, it implants at some place on the wall of the uterus, ideally sort of near the top of the uterus, which is called the fundus. It can be more to the front or more to the back. It can be a little lower down. It can really implant anywhere. 

Emily Oster:

The other thing to say about this positioning is placenta previa is a reasonably common diagnosis and occurs when the placenta is basically low in the uterus and is over the cervix. It can be completely over, partially over. What you said about the growth of the uterus is important to that because it is often diagnosed early in pregnancy. Then as the uterus grows, basically the placenta moves out of the way. So actually a very large share, like 90%, of diagnosed previa do resolve.

Dr. Gillian Goddard:

Resolve on their own with no intervention whatsoever.

Emily Oster:

Let’s fast-forward to the end of pregnancy, when I think we have a lot of placental discussion. The first thing that comes up often is the question of whether your placenta wears out — effectively, whether some of the push to not let people go past 41 or 42 weeks of pregnancy is  feeling like this placenta is a temporary organ. It only has so much time, and if it wears out, that can be dangerous. How much do we know about whether that happens, that process, et cetera?

Dr. Gillian Goddard:

We’re really just starting to understand exactly what’s going on in that process. There are some relatively simple hormones called peptide hormones that impact the way that the mother’s vasculature is connected to the placenta. We think that these hormones are important and may play a role in some of the complications that can happen in the third trimester. Maybe these hormones have an impact on triggering things like labor and what we often talk about as placental sufficiency or insufficiency, how much capacity the placenta has to do its job. It may be related to some of these hormones that affect the blood flow on the mother’s side to the placenta.

Emily Oster:

At the end of pregnancies, you go into labor. Let’s imagine you have a vaginal birth, you deliver the baby, and then the third stage of labor is the delivery of the placenta. Some people find that surprising. It’s typically like one contraction and the placenta comes out, ideally all in one piece. So one thing that can happen is the placenta can get stuck and not come out. Why is that of concern?

Dr. Gillian Goddard:

Because if there are pieces of the placenta stuck or if the whole placenta is stuck, it doesn’t allow the blood vessels on the mother’s side to clamp down and stop delivering blood. It allows for really significant hemorrhage on the mother’s side, which can be quite dangerous.

Emily Oster:

Assuming that your placenta is delivered at the end of the third stage of labor, it’s there. They put it in one of those bedpans. Then we’re going to get to the most important question in this interview, which is: should I eat it?

Dr. Gillian Goddard:

I don’t think that there are any proven benefits of eating your placenta.

Emily Oster:

Some nice people will take your placenta and turn it into pills. What’s the evidence on those?

Dr. Gillian Goddard:

There’s no proven benefit to that whatsoever. Some of the theories are that it might help with your recovery after pregnancy because there’s a little bit of iron in the placenta, but literally there’s 90 milligrams of iron in your placenta at the end of pregnancy. That’s like two days’ worth of iron supplements that are available over the counter.

Emily Oster:

It does seem like it would be hard to see how you come up with that. After this experience, I would not have thought the first thing you would do is be like, throw that on a stick and put it over the fire.

Dr. Gillian Goddard:

It’s not very appealing. I don’t know if you’ve looked at a placenta before, but it’s a fascinating thing to look at. It’s two-sided. You can tell which side was which, but I can’t say that it looks particularly appetizing.

Emily Oster:

You’re an endocrinologist. It seems like this is an extremely interesting organ that grows by itself and is full of interesting hormones and bosses the hormonal system.

Dr. Gillian Goddard:

It doesn’t boss the hormonal system; it bosses the entire body around. It changes everything about your physiology. It changes how food moves through your gut. It affects every one of your organ systems, which is why I love it so much. Unlike many glands, it is an endocrine gland, and unlike many glands, it makes this whole menu of hormones. It doesn’t just make one hormone or two hormones, it makes eight or 10 hormones. Those are just the ones that we understand. It does that in a really organized and sort of specific way that we really don’t even completely understand how it does what it does. I would love to know more about it.