Placenta
From ChildWiki.com
The placenta is a temporary female organ that functions as a union between the fetal and maternal structures. The placenta is necessary for fetal development and survival.
By the time the fertilized egg travels from the fallopian tube to the uterus, it will be already divided in a handful of cells. This bundle of cells, a blastocyst, will attach to the uterine wall. Soon, the outer layer of cells, the trophoblast, begins its development into the placenta.
Once completely formed, the placenta serves as a flesh bridge between the mother and the baby, traversed by a complex system of blood vessels.
The placenta is completely formed from fetal cells. This is part of the reason why the tests meant to detect chromosomal abnormalities of the fetus are made by extracting a part of tissue from the placenta (at the beginning of the pregnancy, during week 6 and week 11 of pregnancy and analyzing it. The placenta and the fetus are genetically identical.
Once formed, the placenta continues to grow in order to provide fetal needs. The placenta reaches maximum thickness at 32 weeks, after which it starts thinning slowly.
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[edit] Placenta's Shape and Dimensions
At a term birth, the placenta will usually weight about 1/7th the baby's weight. It is round in shape, probably as large as a large plate (20-25 centimeters in diameter) and about 3 centimeters thick.
It has two distinct faces: one fetal and one maternal. The fetal part is flat, smooth, almost silky. Its surface is covered in blood vessels that make it look maroon. Inside the fetal section is an insertion of the umbilical cord, which looks like a reddish-blue tube and contains three blood vessels, the umbilical vessels: two arteries and one vein.
The placenta is covered in a firm gelatinous substance, which helps prevent the forming of nodes or curls.
[edit] Placenta's Role and Functions
During pregnancy, the maternal blood does not go directly into the fetal vessels. The two blood circuits are separate. The exchanges between them are made with the help of the complex vascular system that is present in the placenta.
It has been estimated that the maternal blood flow through the placenta during week 20 is of 300ml per minute, and in week 40 of 600ml per minute. The area of the placental surface that is used for blood circulation and exchange is 11 square meters.
All the nutritional elements that the fetus requires comes from the maternal blood through the placenta, this is why diet is important during pregnancy. All residual products that the fetus eliminates will get back to the maternal blood and the mother will eliminate them through urine and feces.
The advantage of this "filter" is that the fetus is safe from toxins and dangerous infections. Though the placenta is a great filtration system, it isn’t perfect. Unfortunately, some infections can pass through the placenta and into the fetal blood, such as: rubella, toxoplasmosis and HIV/AIDS infections.
Certain poisons can also get through the placenta, including alcohol and nicotine, thus smoking and drinking during pregnancy is also discouraged. Medication and drugs pass the placenta as well, reaching the fetus.
Besides the fact that the placenta maintains the life and development of the baby, it also has the function of producing hormones, which are very important for a healthy pregnancy. The increased production of estrogen and progesterone assured by the placenta will stimulate the mammary glands and prepare them for breastfeeding.
[edit] What Happens When the Placenta Is Functioning Normally
If the baby is developing well, is active, and the expectant mother is gaining weight, then the placenta is doing its job. Still, there are cases in which the placenta cannot cope with the needs of the growing fetus.
Placenta issues arise when the blood flow is low (in mothers with a hypertension), or because it hasn't developed well, started aging and is now less efficient. These issues can lead to a placental insufficiency. Consequences of placental insufficiency are: the mother doesn’t gain enough weight, the fetus becomes small for its gestational age, and fetal movements are reduced.
If this occurs, the mother will be advised to rest more in order to raise the blood flow through the placenta. Also, the obstetrician may order a non-stress test to graph fetal movements. Other placental monitoring tests are echography and blood tests. If the function of the placenta is severely affected, labor and birth may be induced earlier.
[edit] Separation and Expulsion
After birth, the third stage of labor arrives: the separation and expulsion of the placenta. It will take around 10 minutes and is much less painful than birth itself.
After the baby is born, the following contractions will instigate the separation of the placenta and its elimination through the vagina. The uterus will continue to contract, closing all the resulting open blood vessels from the separation of the placenta and limiting the bleeding.
There are two ways in which this stage is performed.
- Most women have an active labor stage that initiates the decrease in bleeding. Right after birth, an oxytocin injection is given to the mother that will produce uterine contractions. Several minutes after the baby is born, the doctor will place a hand onto the mother's abdomen, and with the other hand he will pull on the umbilical cord to eliminate the placenta.
- The other way to do this is by eliminating the placenta naturally. This process can take between 30 to 60 minutes, until the uterus begins contracting on its own again. This process can be accelerated by placing the baby at the breast, because breastfeeding stimulates the production of oxytocin.
After delivering the placenta, the doctor will examine it and the attached membranes to determine that it is whole and there are no remaining pieces in the uterus. Any pieces left in the uterus will cause internal bleeding. There are some cases in which the elimination of the placenta cannot be completed due to non separation. These cases require surgical intervention.
[edit] Placenta Problems During Pregnancy
Normally, the placenta is developed onto the upper side of the uterus, but it can develop onto the inferior side. This is usually seen at the echography from week 20. In this case, the ultrasound will be redone later on, because in most cases, as the uterus enlarges, the placenta will move up towards the upper walls.
Nevertheless, there are cases in which the placenta remains inferior, covering the internal opening of the cervix. This condition is called, (placenta previa). In these cases, the baby's exit is blocked and a cesarean is required. Placenta previa can cause bleeding.
Another cause for bleeding in advanced pregnancy is placenta abruptio, when the placenta detaches itself from the uterus while the woman is still pregnant. When this happens, the mother is prescribed bed rest in the hospital until the baby reaches fetal maturity and can be delivered safely.
