10 fascinating facts about the placenta you probably didn’t know!

March 2020

The placenta, the lifeline between a mother and baby, is the organ where the connection between baby and mother is first established. According to the NIH, it is “the least understood human organ and arguably one of the most important organs in the body.” It influences the health of a woman and her baby during and even after pregnancy. In honor of this incredible organ, we listed ten fascinating facts about the placenta.

1. Small but mighty - Shaped like a parachute, the placenta is a highly specialized organ that helps support the development of your baby. An average placenta is 9 inch in length, about 1 inch thick, and typically weighs just over 1 pound. Blood from both mom and baby pass through the placenta but never mix. Every minute during the pregnancy, almost about 550 milliliters of blood gets pumped into the uterus to exchange nutrients with the placenta for your baby. That alone is amazing (and also explains why pregnancy is so exhausting.)

2. One organ, multiple functions - The developing fetus doesn’t eat or breathe and relies solely on its mom for nutrients and oxygen. The placenta acts as the baby’s lungs to supply oxygen and remove carbon dioxide. It also acts as baby’s kidneys to filter out waste products such as urea, uric acid, and creatinine. It also helps the fetus in keeping its temperatures steady and acts as an immunological barrier protecting the fetus from being attacked by the mom’s immune system.

3. It’s not a maternal organ - In fact, the placenta develops from the fertilized egg, which means, just like the embryo, the placenta is half from mom and half from dad. The placenta begins to form right after the fertilized egg implants in the uterus wall around 6 to 7 days after conception, and it continues to grow with the baby to supply its growing needs.

4. The placenta is also a gland - The placenta acts as a gland that secretes hormones during pregnancy like Human Chorionic Gonadotropin (hCG), Estrogen, Progesterone, and Human Placental Lactogen which play an essential role in supporting your growing baby and prepare you to motherhood.

5. Placenta gives babies “starter” immunity - Mother’s antibodies are passed through the placenta during the third trimester and help the baby prepare for life outside the womb. These antibodies build up the baby’s initial immune system and offer protection for up to six months until the baby can produce its own antibodies.

6. Identical twins may share a placenta - Fraternal twins, developed from two separate fertilized eggs, will always have 2 placentas. However, the number of placentas in identical twins is determined by the time at which the fertilized egg splits. If the egg splits before the placenta develops, each baby will have its own placenta. If the egg splits after the placenta has formed, both babies will be sustained by one placenta.

7. Fetal cells can pass through the placenta to protect and heal the mother’s organs- Fetal stem cells can transfer to the mother during pregnancy, and they seem to target sites of injury. These cells have been found in the skin, liver, kidney, and bone marrow. This phenomenon is called fetomaternal microchimerism. The significance of fetomaternal microchimerism remains unclear.

8. The only disposable organ - A placenta will grow in every pregnancy to support the growth of your baby. Once its mission is complete, it is not needed in the body anymore, and unless you decide to store it, it will be disposed of as biological waste.

9. It prepares your body to breastfeed - The placenta produces high levels of progesterone to support the growth of your baby. Progesterone suppresses the action of prolactin, which triggers milk production. Once the placenta is delivered, the progesterone levels drop, which triggers prolactin to signal the body it’s time to produce milk.

10. The placenta can help us fight cancer - The placenta has the unique ability to grow and infiltrate the mom’s body without being attacked by the mom’s immune system. This process is highly regulated, and the placenta “knows” to stop infiltrating before causing harm to the mother. Understanding the mechanism the placenta uses in this process will allow cancer researchers to better understand how tumors grow without being stopped by the immune system.

As you can see, the placenta is quite a remarkable organ during pregnancy. However, its benefits extend well beyond pregnancy and can offer hope that will last a lifetime. You can learn more about preserving the placenta after birth here.

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