The placenta is arguably the least studied of all human organs and tissues. Each one of us comes into the world attached to one: the lifeline that supplies oxygen and nutrients from the mother’s blood, and which removes carbon dioxide and other wastes via the same route. In most cases, the placenta does what it’s expected to do, and few of us give it any thought.
Under usual circumstances, placental cells arise from the early embryo. The placental membranes fuse with the lining of the uterus, forging a connection between maternal and fetal circulation. Interestingly, this ability derives from the genes of ancient viruses, which once infected the cells of our mammalian ancestors and have long since been repurposed 
to establish this most important early life connection. In addition to protecting the fetus from the mother’s immune system, the placenta also acts as a barrier against toxins and infectious organisms such as bacteria and viruses.
But just because the placenta usually does its intricate job well doesn’t mean that we can afford to ignore it. Sometimes, this benevolent cellular invasion can go terribly wrong.
Occasionally, when there is a scar in the uterus from an earlier surgery (such as a prior cesarean delivery), the placental cells invade the uterine muscle. In other cases, it may penetrate through the uterus and invade the bladder and bowel. This can threaten the mother’s life or may require the uterus to be removed following cesarean delivery.
At other times, the placenta fails to forge a strong connection to the maternal circulation. This condition, known as preeclampsia, affects 3-6 percent of all pregnancies. It can occur suddenly, without warning, and may result in seriously high blood pressure for the mother or even potentially fatal complications. The supply of oxygen and nutrients to the fetus may also be impaired. There is only one cure—delivery of the baby. If delivery is needed early, then the baby will be born preterm. Preterm delivery can be life threatening for the newborn, and can increase the chances for such serious, lifelong conditions as intellectual disability, blindness, and cerebral palsy. As adults, individuals who were born preterm are at higher risk for diabetes and heart disease.
Given the tremendous importance of the placenta in human health and development, my colleagues at NICHD and I are proposing a new, intensive effort to unlock the secrets of the placenta. Information from such an effort could lead to new treatments for many of the conditions affecting the placenta, and, perhaps, even prevent them from occurring. Our proposal, “The Human Placenta Project: Placental Structure, Development, and Function in Real Time,” appears online in the journal Placenta.
We invite other federal agencies and non-governmental research organizations with interests in maternal and child health to join with us in this exciting new endeavor, including the development of new means to routinely monitor the placenta’s day-to-day development and function. Currently, efforts to study the placenta are largely limited to examining placental tissues after the birth of the infant. Although we’ve learned a lot from such efforts, there’s a limit to what they can provide. Consider, for example, how difficult it would be to treat heart disease if we couldn’t monitor heart function in living patients, but were limited to examining heart tissue after a heart attack patient had died. The Human Placenta Project seeks not only to make more effective use of existing technologies to monitor the placenta, but also to develop new technologies expressly for this purpose.
As a start, we are planning a scientific meeting later this spring, which will assemble not only international experts in placental biology, but also experts from other fields, who can provide other creative insights. We’ll ask them to identify the most promising scientific opportunities, with the goal of developing an initial research agenda for the HPP.
It has long been known that the placenta plays a key role both in fetal development and in maternal well-being during pregnancy. However, placental conditions can pose not only an immediate threat to a pregnancy, but may also have longer term consequences – for both the fetus and the mother. For example, later in life, women who have had preeclampsia are at increased risk for heart disease later in life. Another condition linked to the placenta, gestational diabetes, conveys an increased risk for diabetes later in life. Similarly, evidence indicates that infants born in pregnancies affected by placental disorders may be at increased risk for obesity, heart disease, and diabetes.
A concerted effort to understand the placenta and monitor its function offers not just the prospect of improved health for pregnant women and the infants to whom they will give birth, but for adults as well.
Addendum
I would like to congratulate Yoel Sadovsky, Elsie Hilliard, and their colleagues at the University Of Pittsburgh School Of Medicine for winning the prestigious Cozzarelli Prize in the Biomedical Sciences. Funded in part by the NICHD, the researchers showed how the cells of the placenta can prevent viruses from crossing from the mother’s blood into the fetal circulation. In laboratory cultures, they also showed that this ability can be transferred to other kinds of cells. The finding opens up the possibility that this defense of the placenta might one day be used to prevent the spread of viral diseases. I believe this recent accomplishment illustrates the potential of the Human Placenta Project to improve human health.
Our Website features a podcast interview with Dr. Sadovsky about this study, recorded last August.
Originally posted: March 19, 2014
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