The placenta, or “afterbirth,” was previously considered a simple, relatively unimportant organ. However, over time, researchers have realized that it plays a critical role not only in fetal development and maternal health during pregnancy, but also in the long-term well being of both mothers and their children. Although its importance is now generally recognized throughout the medical community, our knowledge of exactly how the placenta functions is limited. Also limited is our understanding of dangerous health issues related to placental abnormalities.
What we already know about the placenta and pregnancy complications
Although the placenta remains somewhat shrouded in mystery, its basic functions are known. During pregnancy, it develops from a small cluster of cells into an organ that weighs over a pound. In an article for The New York Times, Apoorva Mandavilli notes that, “It often is compared to an aggressive cancer. But a more apt metaphor might be a military invasion, as 90 percent of the placenta is made up of cells not from the mother but from the fetus” (1).
Placental cells specialize to do the work of the heart, lungs, liver, and kidneys until the fetus has developed enough to function outside the womb. The placenta delivers oxygen, nutrients, and important hormones to the fetus. It removes fetal waste products, such as carbon dioxide. Additionally, it protects the fetus from stress, germs, and chemicals.
If the placenta does not function properly, the consequences can be serious. We know that placental issues can contribute to pregnancy complications such as the following:
- Preeclampsia and eclampsia
- Intrauterine growth restriction (IUGR)/fetal growth restriction (FGR)
- Premature birth
- Placental abruption
- Maternal stroke
- HELLP syndrome
Babies born to mothers with abnormal placentas may experience poor perfusion and oxygenation, which can lead to forms of neonatal brain damage such as hypoxic-ischemic encephalopathy (HIE) and cerebral palsy (CP), among other birth injuries. And long-term, mothers with abnormal placentas are at higher risk of chronic conditions such as heart disease, diabetes, and kidney disease. (1, 2).
The placenta and sex differences
Researchers have found evidence that female fetuses are more resilient to stress from placental issues than are male fetuses. A recent analysis (3) identified 58 genes that are expressed differently in female fetuses, which may confer protection from miscarriage, stillbirth, and premature birth, all of which are more common in pregnancies involving a male fetus. Increased resistance to placental stress could also help to explain why females are less susceptible to neurodevelopmental disorders such as schizophrenia, A.D.H.D, autism, dyslexia, and Tourette’s. Other researchers (4) examined genes linked to schizophrenia, and found that these genes are activated at higher levels when a pregnancy is under stress. However, this effect was less dramatic in females than in males. Dr. Weinberger, an author on this study, told The New York Times that, “I’m very confident the same story is going to be there for autism, A.D.H.D., and other developmental behavioral problems” (1).
Real-time knowledge of placental health
Many studies of the placenta have involved dissecting the organ after delivery. There are also prenatal tests that can assess placental health during the third trimester. However, having an understanding of placental health after delivery or in late pregnancy does not do much to further knowledge of – or better yet, prevent – placental complications that occur in early pregnancy.
As Dr. George Saade, chief of obstetrics at the University of Texas Medical Branch explained, “It’s like studying cardiac disease or any other medical condition just by doing an autopsy” (1).
Fortunately, researchers are hard at work developing methods that could provide information about placental health in real time, throughout a pregnancy. Possibly methods include magnetic resonance imaging (MRI), ultrasound technology, blood tests, and oximetry.
In May of 2014, the National Institute of Child Health and Human Development (NICHD) held its first conference focused on the placenta, and launched the Human Placenta Project (HPP) (5). Today, the HPP is developing and improving methods for assessing placental development and wellbeing in various stages of pregnancy. They aim to identify non-invasive markers that predict pregnancy complications, and ultimately to develop medical interventions that could prevent placental abnormalities and improve outcomes for mothers and babies.
To learn more about the HPP, you can visit their website here: https://www.nichd.nih.gov/research/supported/HPP/default
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- Mandavilli, A. (2018, December 03). The Placenta, an Afterthought No Longer. Retrieved December 6, 2018, from https://www.nytimes.com/2018/12/03/health/placenta-pregnancy-health.html?action=click&module=Editors Picks&pgtype=Homepage
- Preeclampsia: MedlinePlus Medical Encyclopedia. (n.d.). Retrieved December 6, 2018, from https://medlineplus.gov/ency/article/000898.htm
- Gonzalez, T. L., Sun, T., Koeppel, A. F., Lee, B., Wang, E. T., Farber, C. R., … & Rotter, J. I. (2018). Sex differences in the late first trimester human placenta transcriptome. Biology of sex differences, 9(1), 4.
- Ursini, G., Punzi, G., Chen, Q., Marenco, S., Robinson, J. F., Porcelli, A., … & Seidel, J. (2018). Convergence of placenta biology and genetic risk for schizophrenia. Nature medicine, 24(6), 792.
- Grady, D. (2018, January 19). The Mysterious Tree of a Newborn’s Life. Retrieved December 6, 2018, from https://www.nytimes.com/2014/07/15/health/the-push-to-understand-the-placenta.html?module=inline