When it comes to pregnancy, most attention rightly has been focused on the baby-to-be and the pregnant mother.  The mother and baby of course remain the key focus of a pregnancy.  But as we so slowly begin to understand the mysteries of how a fertilized egg turns into a baby, the placenta continues to be more and more fascinating.

A recent article about the placenta brings much of the new findings to light, https://nyti.ms/2zCe0ZC.

What is the placenta?

The placenta is, like the heart or spleen, an organ of the body, with a vast universe of cells organized a central purpose.  In the case of the heart the purpose is obvious, it is to pump the blood, as well as monitor fluid status in the body.

For the placenta, the purpose is also clear, it is to maintain the pregnancy and guide the fertilized egg in its journey from a single cell, to a full-fledged person ready to be born and live in the open-air world.

The word placenta comes from the Greek word plax or plak, which simply means a flat plate.   It’s the root of another medical word, plaque, which is a flat plate of cells.  The word originates from the early stages of the placenta, when it really looks like a flat plate of cells.

The emergence of the embryo and placenta

One of the most amazing facts about the placenta is that it is made mainly from the baby’s cells.  We tend to think that once the egg is fertilized and divides into a ball of dividing cells, that the ball of dividing cells is going to be the baby.  But it turns out at that very early stage, in the first days of pregnancy, the vast majority of those dividing cells will be the baby’s placenta, only a tiny smear of cells on that ball will become a person!

It makes clear what a top priority biology makes of the placenta.  First, the egg must be fertilized, but once that happens, most cells that are created are devoted to keeping that emerging person healthy and thriving, so it is the placenta first, then the baby that develops.  That flat plate of cells that becomes a person is the embryo until it is more fully formed at which point it is called a fetus.

The first task of the placenta is to invade the wall of the mother’s uterus, and it is a true invasion, the placental cells burrow the sphere deep into the uterine wall, neutralize the mother’s immune system ability to defend itself by destroying the placenta and embryo, change the architecture of the uterine blood vessels so that they grow towards the forming placental blood vessels to ensure steady supply of oxygen and nutrient and clearance of embryo’s wastes.

In short order, the cells of the placenta establish the functions of heart, lung, kidneys, really many organs, while the embryo develops all these organs over the following weeks and months.

The impact of placental health on the subsequent health of the mother

Since the placenta literally takes command of a large blood vessel system, the blood vessels of the mother’s uterus, it has a huge impact n the mother’s whole circulatory system.  It is this impact that leads the placenta controlling the mother’s blood pressure, fluid balance, really the integrity of her entire blood vessel system.  When this goes wrong, the mother’s blood pressure can rise, her blood vessels become leaky causing leg swelling, and her kidney blood vessels become leaky causing protein to appear in her urine, a condition called pre-eclampsia which is very common and causes quite a bit of complications in pregnancy including premature birth.

Complications from placental interactions with the mother’s uterus can cause long term hazards to the mother’s health, including later risk for heart disease and stroke.

A very troubling field of placental research is opening up a tremendous range of understanding about how the cells from the embryo, and later the fetus, actually get through the placenta into the mother’s circulation, and live their for many years and decades.  It is thought that the entry of another person’s immune cells, namely the embryo and fetus, allows for these persisting cells to attack the tissues of the mother.   There is growing evidence this does occur, and may be a large part of the reason that auto-immune problems like lupus and rheumatoid arthritis are so incredibly more common in women than men.  It may be that much of the auto-immune inflammation seen in women who have been pregnant may actually not be auto-immune, but initiated by cells from the babies of the pregnancies.

Properties of the Placenta Impact Differences in the Health of Male and Female Babies and Students

In nearly every study of how the health of male and female newborn babies, female babies are shown to have slightly, but reliably, greater health in a number of different ways.  Male fetuses suffer more miscarriages than female fetuses, males are more likely to be born prematurely, and in the NICU, the survival rates are slightly higher for female newborns than males.  In school years, boys far outnumber girls in the chances of developing abnormalities of neurocognitive function, such as ADHD, learning disorders, and autism spectrum disorder.

Later in life, boys are far more likely than girls to develop schizophrenia.

Recent findings in the study of the placenta have uncovered some clues to suggest the male placenta may play a role in these outcomes.

A key finding is that when the placenta is stressed during a pregnancy, through trauma or infection or dehydration, the male placenta is more likely than the female placenta to be affected by the stress.

Another difference is noted in the expression of genes in male and female embryos. Remember, two people may have the same DNA, but express the genes at different times and in different patterns.  It has been found that over 50 genes shared by all embryos are expressed more in male than in female embryos.  A major difference between male and female DNA is with the X-chromosome.   All people, male or female, have 22 pairs of matching chromosomes, one of each of the 22 pairs are from Mom and the other one of the pair is from Dad.

But then there is a 23rd pair of chromosomes.  For nearly all female humans, there is a pair of these chromosomes too, one from Mom and one from Dad, just like the other 22 pairs.  I say nearly all because a number of females have only one X chromosome, a situation called Turner Syndrome, which is fairly rare.   For nearly all male humans (again, there are rare variations such as XYY), their pair of X chromosomes is quite different, they have one X chromosome from Mom, but the matching chromosome from Dad is a tiny, tiny version of that chromosome, and called Y.  The Y chromosome contains very few of the total number of genes.

What does this mean?

For all the 22 pairs in everyone, and the X-X pair in nearly all females, if there is a problem with one gene on one of the pair, there is a good chance the other of the pair will have the normal gene.  But for males, they have only one copy of the X chromosome, so many, many genes on this chromosome stand alone, any problem with them and the child is affected by the abnormality.

Of the 50 plus genes expressed more commonly in males than females, many are indeed on the X chromosome, explaining why boys are more affected.

A specific set of genes, related to schizophrenia, is seen to be more active when the pregnancy is stressed, and these genes are seen to be activated in the male placenta more than the female in these situations.  Researchers find it very plausible a similar mechanism may underlie the male preponderance of troubles with other aspects of cognition such as those seen in autism spectrum disorders, ADHD, and learning disorders.

BOTTOM LINES

1. We have tremendous interest and even reverence for many key organs of our lives.  The heart, our lungs, certainly our brains, come to mind.  But there is only one organ that gets thrown away after we are born that is just as incredible, the placenta.
2. We tend to think the ball of cells that the fertilized egg creates soon after conception is all baby, but really it is nearly all developing placenta.  That organ serves as the heart, lung, kidneys, of the emerging embryo until their organs are crafted.  That ball of cells, the early placenta is also in charge of invading the mother’s uterus and sustaining the pregnancy.  This makes the placenta a truly master organ.
3. Given the centrality of the placenta to the very existence of pregnancy and the development of the embryo into a fetus and then baby, it makes sense that problems with the placenta could lie at the heart of a range of health issues.
4. Stresses on the health of the placenta affect male more than female embryos and fetuses, which may explain why boys are more likely to have neurobehavioral dysfunctions.
5. The command of the placenta on how the mother and baby-to-be blood flows interact help explain why troubles with that function can lead to abnormalities in Mom’s blood pressure, insulin function.   Leakage of fetal cells into the mother’s circulation may explain why auto-immune diseases are far more common in women who have been pregnant than men.

The placenta is an organ vital to all our lives, it is quite fascinating to learn more about its impact on all our lives.

To your health,
Dr. Arthur Lavin