Hi.
My name is Mana Parast, and I'm a perinatal pathologist and stem cell scientist
at the University of California, San Diego.
And today, I'm going to tell you about a very intriguing organ, an organ that none of us
would be able to survive the intrauterine period without.
And that organ is the placenta.
So, what is the placenta?
It is the connection between mom and baby.
It's also known as afterbirth, because it's delivered after the baby.
And those of us that study the placenta in cases of pregnancy complication also know it
as a diary of intrauterine life.
Now, placenta... and the placenta is literally forming a connection between mom and baby.
On one side, it's connected to the baby via the umbilical cord.
This is the connection through which the baby's blood flows into the placenta in order for it
to be loaded up with oxygen and nutrients, and then goes back to the baby.
On the flip side, it's attached to mom, and specifically, to the uterine lining called decidua.
Now, placentas come in all shapes and sizes.
This one has the umbilical cord attached to one side.
This one seems to have a little bit of extra tissue on the side.
This one looks a little pale, maybe a little bit lumpy on the fetal side.
And this one looks like it has an abnormal umbilical cord, and is a little bit green.
So, is there a significance to these different shapes and sizes and colors?
Well, let's examine them together.
So, with some of these placentas, what they help us with is to confirm clinical findings.
So, this placenta, with a little bit of extra tissue on the side... actually, what this is
is a blood clot that has been accumulating over the period of pregnancy, and led to
the premature delivery of this placenta at 27 weeks.
So, this finding actually confirms the clinical diagnosis of chronic abruption.
Sometimes, placentas can provide a hint at a diagnosis of an underlying disease in mom.
So, when this placenta came out, it was associated with a small-for-gestation baby.
On exam, we could see that the placenta shows areas of infarction or dead tissue.
And microscopically, this placenta was diagnosed with massive perivillous fibrin deposition.
This is a condition that's associated with maternal autoimmune disease.
And in fact, this mom went on to be diagnosed with lupus.
And this diagnosis came about because of this placental examination.
And it's important to... that she received this diagnosis, at this point in time,
because for her next pregnancy she will be able to be treated to prevent another instance of
intrauterine growth restriction.
At other times, placentas can provide a cause of stillbirth.
So, in this case, the placenta is shown to have a long hyper-twisted umbilical cord.
And a placental exam can give us some insight into recurrence of stillbirth
in subsequent pregnancies.
So, with the long umbilical cord, because the length of the cord is at least
partly determined by genetics, this woman is at a slightly increased risk of having stillbirth
due to a long cord in a subsequent pregnancy.
So, what I've shown you is that the placenta can really be the diary of intrauterine life.
But more recently, it's been called "the least understood human organ"
by the National Institute of Child Health and Human Development.
And this is in fact true as well.
We don't really understand how the placenta develops.
We don't have a good test to test its function during an ongoing pregnancy.
And even worse, we don't have any drugs to target the placenta when there is a pregnancy complication.
So, let me tell you about another devastating disease during pregnancy,
which is called preeclampsia.
Preeclampsia has also been called "the silent killer."
The symptoms of preeclampsia develop during the second half of pregnancy,
even though the disease is thought to originate early in pregnancy.
The symptoms include high blood pressure, and high protein in the urine -- or proteinuria --
which is a result of kidney dysfunction.
But the symptoms can vary.
They can range from just purely high blood pressure, or gestational hypertension,
all the way to eclampsia, where there's seizures, and to HELLP syndrome,
which includes liver failure and clotting disorders.
Preeclampsia happens in 5-8% percent of pregnancies worldwide.
Other than maternal complications, there is also neonatal complications,
the most common of which is intrauterine growth restriction.
There is no cure for preeclampsia except delivery.
And as a result, it's the leading cause of preterm deliveries.
A placenta from... a preeclamptic placenta shows a lot of pathology.
So, what you see here is a placenta with an infarct, or an area of dead tissue.
In addition, these placentas show evidence of maternal vascular disease, as is evident
on the clinical side by high blood pressure in mom.
But even around the infarction, or the dead tissue, the placenta, under the microscope,
appears very abnormal.
Basically, it shows evidence of abnormal placental development.
And we're not clear as to how this happens.
In order to better understand this disease, we have to understand placental development better.
Now, the placenta develops from the embryo, from... in particular, from the outer cells
of an embryo that are called trophoblast.
This outer layer of cells -- the trophoblast -- proliferate, expand, and differentiate
in order to give rise to the placenta at term.
The word trophoblast comes from the Greek word tropho, meaning "to feed."
And in fact, this is the primary function of these cells, in order to be able
to access maternal blood and then provide it to the growing placenta, and therefore the fetus.
The trophoblasts begin at a progenitor cell called a cytotrophoblast, or CTB.
And they have to differentiate into two different subtypes.
One is extravillous trophoblast, or EVT.
And the other is a multinucleated syncytiotrophoblast, or STB.
Now, EVT, extravillous trophoblasts develop early in pregnancy.
And they're perhaps the most crucial to pregnancy success.
So, before pregnancy, the maternal vessels look like this.
They are basically very small, and they can carry very little blood to a growing baby.
However, in... during the first trimester of pregnancy, the extravillous trophoblasts
actually invade and remodel maternal vessels, thereby allowing these vessels
to carry more blood to the growing feto placental unit.
The syncytiotrophoblasts develop in functional units units of the placenta
called the chorionic villi.
This is where the gas and nutrient exchange actually happens.
These units are comprised of fetal blood vessels in the middle and a layer of cytotrophoblasts,
and these progenitor cells then fuse to form the multinucleated syncytiotrophoblasts.
Syncytiotrophoblasts secrete the pregnancy hormone HCG.
And they are the cells that are responsible for gas and nutrient exchange.
If either one of these cell types doesn't differentiate properly, the result is
abnormal placental development.
So, if the extravillous trophoblasts, or EVT, don't differentiate well,
the placenta doesn't receive enough maternal blood.
If the syncytiotrophoblasts, on the other hand, don't differentiate properly,
that results in improper, insufficient gas and nutrient exchange.
Both of these can result in placental diseases, including preeclampsia and intrauterine growth restriction.
So, in summary, the placenta, as I've explained, is a diary of intrauterine life.
Placental examination cannot just confirm clinical findings, but it can also identify
underlying maternal disease.
It can provide a cause for unexplained stillbirths.
I've also explained that abnormalities in placental development can lead to
pregnancy complications, including preeclampsia and IUGR.
And I've also summarized the development of placental cells, or trophoblasts,
specifically from a cytotrophoblast progenitor state into either extravillous trophoblasts, or EVT,
which are invasive cells that help access maternal blood, or syncytiotrophoblasts, or STB,
which are multinucleated cells which help in gas and nutrient exchange.
I hope you stay tuned for the second part of the talk, where I'm going to discuss
how we can model and better understand human placental development.