Placenta

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Philippe Gloaguen
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How the placenta works

The placenta is a very important and valuable organ during pregnancy. During this period, the mother's womb forms placenta, a deciduous organ, i.e. temporary, which has the purpose of nourishing, protecting and supporting the growth of the fetus. But how the placenta works? Its shape is that of a disc, which adheres to the wall of the uterus and the maternal vessels enter it on one side, and the fetal vessels on the other. There is no direct contact between maternal and fetal blood, the passage of nutrients and oxygen occurs through a thin membrane, called the "placental barrier".



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What is the placenta

The placenta represents the main physical bond between mother and child, it is no coincidence that it is an organ common to the pregnant woman and the fetus. A part of the placenta originates from the maternal organism, that is, it is constituted by the uterine endometrium (defined as decidua) while the remaining part has fetal origins because it is formed from the chorionic villi, i.e. extensions generated by the outer layer of embryonic cells. The placenta provides for all the needs of the fetus: it nourishes it, protects it and allows an intimate bond to be established with the mother. It is a very important bond made up of care, dependence and autonomy which, in some respects, will also have its importance in the extrauterine life of mother and child.



What is the placenta for

The primary function of the placenta is to allow metabolic and gaseous exchanges between fetal and maternal blood. The fetus and placenta are connected to each other via the umbilical cord while the mother's organism communicates directly with the placenta through blood-filled sacs called blood lacunae. But the placenta performs numerous other functions:



  • it supplies oxygen to the fetus and removes carbon dioxide through the placental barrier, that is the thin layer of cells that separates the chorionic villi from the maternal blood;
  • purifies and regulates the body fluids of the fetus;
  • provides the fetus with the necessary nutrients, including glucose, triglycerides, proteins, water, vitamins and mineral salts thanks to its permeability with respect to these nutrients present in the maternal blood;
  • it allows the passage of antibodies to endocytosis and at the same time prevents that of numerous pathogens (with some exceptions such as rubella viruses and toxoplasmosis protozoa);
  • prevents the passage of many harmful substances for the fetus even if some can still pass through it constituting a danger for the baby (caffeine, alcohol, nicotine, some drugs, drugs ...);
  • produces the hormonal substances necessary for pregnancy: human chorionic gonadotropin (HCG), progesterone, estrogen and prolactin.

The position of the placenta depends on where the implantation of the embryo takes place in the endometrium, it can therefore be anterior, posterior, or lateral and this affects neither pregnancy nor delivery. However, it can happen that the placenta is located lower than normal: in this case we are talking about low placenta or placenta previa. In about 5% of early-stage pregnancies, the low-lying placenta is found, which in most cases returns to its normal position as the pregnancy progresses. This occurs because the uterus, by increasing in size, pushes the placenta higher. To correctly diagnose placenta previa, it is necessary to check its position around the 35-36th week of gestation.

Generally, placenta previa makes it necessary to carry out delivery by caesarean section, especially in cases of central placenta previa. In this case, an obstruction of the cervix occurs which prevents the fetus from passing through the birth canal.

Un attempt at natural childbirth in these conditions it would cause lacerations in the placenta which in turn could cause serious bleeding that can seriously endanger the health of the mother and baby. To evaluate the functionality of the placenta in normal conditions, the most reliable parameter is above all that of fetal growth: if the size of the fetus corresponds to what is expected based on the gestational period and the quantity of amniotic fluid is normal, it means that the placenta works well. Other parameters that are evaluated through ultrasound examinations are the umbilical artery flowmetry, which evaluates the functionality of the placenta based on the conditions of the fetus, and the uterine arteries flowmetry, which instead explores the maternal side.

Read also: Placenta previa, what it is and what it can entail

Flowmeter testing is not necessary in all pregnancies, but it is certainly essential in pregnancies at risk for fetal growth retardation in order to monitor the situation and choose the most suitable time for delivery. In some cases in the ultrasound reports the gynecologist can signal the presence of "placental lakes": these are sections of the placenta in which blood circulates more slowly that are rarely associated with placental insufficiency or aging of the placenta and therefore with a growth retardation fetal.

On the other hand, an event that can seriously jeopardize the health of the mother and the baby is that of the detachment of the placenta. This is a real obstetric emergency sometimes associated with hypertension in pregnancy and requires prompt intervention. Clinically, placental abruption manifests itself through abdominal pain and abundant blood loss, so it is very important to contact your doctor immediately in the presence of such symptoms. It is important to emphasize that often it is only the symptoms that allow the diagnosis of placental abruption because the ultrasound examination generally does not indicate any abnormalities. Among other things, to identify the presence of a possible hematoma behind the placenta through ultrasound, it takes time while in these cases it is necessary to intervene as soon as possible.

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