Warning, placenta pictures ahead!
Placenta is a word that evokes a variety of different responses from people. Some are fascinated, some are disgusted, many are indifferent. This organ is often called “the afterbirth” and thought of as something that is to be whisked away and discarded as soon as it’s passed. Many women never get a chance to see their own, but in the growing movement to reclaim natural birth in our culture, more and more women insist on viewing, touching, or even eating their placentas. The day after our second son was born, at home, my husband posted “I almost forgot that there is a placenta in our fridge” on his Facebook status, and the variety of responses was absolutely hilarious. Beyond being something to take care of after the excitement of baby’s birth, though, the placenta has many incredibly important (and incredibly fascinating!) functions, both during pregnancy and during birth.
1) The placenta is the go-between, the gateway between the growing baby and the mother’s bloodstream. Growing alongside the baby in the mother’s womb, it is linked with the mother’s blood and then connects to the baby via the umbilical cord, which enters the baby’s body through the abdomen. This organ is like the filter through which the mother’s blood flows, sending vital nutrients, antibodies, and oxygen through the umbilical vein to the baby, and then receiving de-oxygenated blood and fetal waste through the umbilical arteries.
Perhaps one of the most fascinating things about the placental system is that while the blood flows constantly between mother and baby by way of the umbilical cord, being processed through the placenta, the two bloodstreams don’t actually come into direct contact with one another. There are specific blood vessels that handle maternal blood, and specific blood vessels that handle fetal blood - there is no point when the two blood supplies simply flow into one another.
(the fetal side of a placenta)
2) The placenta releases a specific balance of hormones that prevent the mother’s body from terminating the pregnancy and rejecting the fetus. In a very simplified explanation, in the very beginning of pregnancy there are two major hormones at play - human chorionic gonadotropin, or HCG, and progesterone. (Of course there are a variety of other hormones involved in creating and maintaining a pregnancy, but these ones are the really crucial ones in the beginning.)
Since the placenta itself needs several weeks to form, these hormones originally come from other sources. HCG is first produced from the embryo itself, signaling to the mother’s body that the egg has been fertilized and pregnancy is ready to begin. Receptors in the corpus luteum (the remaining follicle after the egg has been released) then receive this signal from the embryo, and it continues its production of a hormone called progesterone. Without the hormonal signals from the HCG, progesterone levels would become lower and lower towards the end of the monthly cycle, triggering the start of menstruation. But when the egg is fertilized and progesterone levels remain high, the uterine lining continues to develop rather than being shed during menstruation. This ensures a safe, thick lining of endometrium in the uterus, for the fertilized egg to implant and pregnancy to begin.
This delicate balance of HCG from the growing embryo and progesterone from the corpus luteum continues for about 10 weeks past ovulation, until the placenta becomes mature enough to take over. Then the placenta continues the process of producing both of these important hormones, and continues to maintain just the right levels all the way through pregnancy.
3) Another important hormone that is produced by the placenta is estrogen. The levels of this hormone are very low during the early parts of pregnancy, but rise steadily during the second and third trimesters, particularly towards the very end of pregnancy.
There are two important reasons for these increasing levels of estrogen. This hormone turns on the receptors for oxytocin, which is an important step in preparing the uterus for labor. It is the flow of oxytocin that will cause contractions during labor, but it is the estrogen produced by the placenta that prepares the uterus in advance, getting it ready to receive the signals from the oxytocin. Estrogen also helps to prepare the breast tissue for milk production. It causes the ducts and other tissues to grow and develop, in preparation for making breast milk.
4) Have you ever noticed your pelvis and hips getting wider towards the end of pregnancy, perhaps causing your hips to slip or give out once in a while? You can thank relaxin for this sometimes annoying but incredibly important part of pregnancy. Relaxin is another hormone produced by the placenta, and it does just what its name says - it causes ligaments to relax. Part of the miracle of birth is that this relatively small part of a woman’s body is designed for fully developed, sometimes fairly large babies to pass through. Relaxin is a crucial part of that, loosening up the pelvic ligaments to allow the pelvis to open wide enough for the baby to pass through. It can be irritating to deal with the discomfort of your loosening pelvis as you’re trying to move your very pregnant body around for daily activities, but the experience of having this perfectly designed little person emerge from what seems like such a small place makes the discomfort worth it.
(the maternal side of a placenta)
5) Speaking of the end of pregnancy, the placenta has an important role in triggering the start of labor. Remember the hormone called progesterone, which helps to maintain a safe environment for the fetus to grow and develop? One of the important effects of progesterone is to prevent contractions of the uterus. This is obviously a very important step in a healthy pregnancy, and is actually called “the progesterone block” by scientists. The steadily rising levels of estrogen, also released by the placenta, reach a point where they override this function, though. Once the estrogen increases to a certain high enough level, it negates the anti-contraction quality of the progesterone. This causes contractions, the beginning of labor.
The placenta is a fascinating organ, the only organ in the human body that develops for a specific, important purpose and is then expelled because it is no longer needed. Its role in a healthy pregnancy goes so far beyond simply providing nourishment for the baby. The placenta, or more specifically the hormones that are released by the placenta, serve many very important functions, from establishing the environment within the uterus during early pregnancy, to helping trigger the start of labor, and even preparing the breasts to nourish the baby after birth. Perhaps if more people were aware of the incredible ways that this organ helps to establish, maintain, and eventually end pregnancy, we would be less apt to think of it as simply “afterbirth”, a waste product meant to be gotten rid of. Without the placenta there wouldn’t be a pregnancy to speak of, so let’s give this incredible organ the credit it’s due.
What do you think of when you hear the word “placenta”? Did you get a chance to look at or touch your own placenta, or do you intend to?
image credit: moppet65535 via Flickr; moppet65535 via Flickr.
*** Note - this was originally published on a now defunct website in the "birth business." I'm the original author of the post and was proud of my work so I decided to repost it here. :)