Placenta: what it is, when it forms, what it is for, what happens if it works poorly

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In this article

  • What is the placenta
  • How it forms
  • Anatomy and development
  • What is
  • If it doesn't work well

Placenta, what is it

The word placenta comes from a Latin term which means focaccia. In fact, it is an organ which, once fully developed, takes the form of a flattened discoid focaccia.

"He is the only one transitional organ that we have - it is formed only during pregnancy, constituting the interface between mother and baby - and contrary to what is often thought it has entirely fetal origins "explains the researcher Chiara sent, head of the Maternal-Fetal Translational Research Laboratory of the University of our city, which has been studying the biomolecular characteristics of the placenta for years.

Furthermore, the placenta is the only one shared organ between two individuals: for 280 days - more or less - provides the fetus with a continuous flow of food and oxygen and removes waste from the baby's metabolism.

Read also: Pregnancy week by week

How it forms

"The starting point is represented by the union of the spermatozoon to the egg cell: this is how it is formed zigote, a single cell that begins to divide into many other cells. Some of these will give rise to the embryo and others to the placenta "explains Mandò, underlining that precisely because of this origin from the genetic point of view, the placenta has fetal and non-maternal characteristics. analyzed in fetal DNA tests from maternal blood, increasingly popular among prenatal investigations.

The formation of the placenta - or as the experts say, placentation - it is not an immediate process, but it is completed in the first ones 20 weeks of pregnancy, with the differentiation of various cell types. "It is as if it were a construction site which, in order to be fully operational, must have the architect, the surveyor, the workers: each different cell type has its position and its role and all together contribute to ensuring that the placenta works. to the best".

Its development begins with the implantation of the embryo in the uterine mucosa: the cells that will give rise to the placenta immerse themselves in this mucosa and as tiny roots begin to branch.

Read also: Pregnancy with placenta previa

Anatomy and development

At the end of the process the placenta has the shape of a disc on one side attaches itself to the mother's uterus for its entire surface. On the other hand, the capillaries of the disc unite to flow into the veins and arteries of the umbilical cord. At term of pregnancy, the placenta has on average a diameter of 16-20 centimeters, a central thickness of 3-4 centimeters (which reduces to 0,5 centimeters at the edges) and a weight of 500 grams.

"Up to the twentieth week the placenta grows a lot on the surface, while in proportion the embryo first and the fetus then grow less. From the second half of pregnancy this relationship is reversed: the placenta is now well formed and able to function at its best. growth continues but has slowed down and furthermore its thickness is thinned to make room for the fetus which, on the other hand, grows more in these weeks ".

The exchanges of oxygen, nutrients, waste and - as we will see - also hormones occur at the mother-baby interface through an intricate anatomy of blood vessels: those coming from the mother open forming small pools of blood, where they immerse themselves and those coming from the fetus, so as to be able to withdraw and pour substances.

The importance of the first quarter

The formation of the placenta begins soon after fertilization and the first few weeks of pregnancy are very important for a proper placentation. Similarly, we now know that fetal organs are formed in the first trimester, while the baby will take the rest of the pregnancy to grow and "gain weight".


For this reason, in recent years doctors and researchers have begun to insist on the importance of the first trimester for the future of pregnancy and the health of mother and child, and in particular on the importance of lifestyle habits in this first trimester and possibly even earlier: no alcohol and smoking, yes to a healthy diet (varied and balanced, preferably Mediterranean style) and yes to regular physical activity.

What is the placenta for

Exchange of nutrients, oxygen and waste

"The main and best known function is that of provide oxygen and nutrients to the child e return to the mother the waste of the metabolism fetal "explains Mandò.

Production of hormones

Furthermore there is an important endocrine function, that is the production of hormones that are useful both to the mother and to the baby: for example the famous chorionic gonadotropin, the one that is detected by pregnancy tests, but also progesterone, estrogen, placental lactogenic hormone. , placental growth factor and others. Some of these hormones are important for maintaining pregnancy, others for protecting the baby from the mother's immune system.

The "intelligent" placenta

"But beware: the exchanges of substances that take place at the placental level are not passive and random: on the contrary, based on the conditions of the mother (for example her nutritional status and hormonal levels) and of the fetus, the placenta can actively concentrate and sort various substances, in order to optimize the growth of the child ". That's why Mandò likes to say that the placenta is a "intelligent" organ and that pregnancy is not a two-compartment system, but a three-compartment system: mother, baby, placenta.

The barrier function

Another very important function of the placenta is that of protect the baby from many microorganisms: "There are few known viruses that manage to cross it" explains the researcher, underlining that at the moment a lot of research is focused on understanding the possibility of this passage in the case of Sars-Cov-2, the virus responsible for Covid-19. "The available data suggest that there is no vertical transmission, ie passage of the virus from an infected mother to a fetus, but we need to continue studying". Mandò's research group, on the other hand, is trying to understand if the more serious symptoms of Covid (pneumonia and respiratory deficiencies) can hinder the oxygen transport function of the placenta, causing indirect negative effects on pregnancy.

Read also: Anterior placenta Read also: Flowmetry or Doppler in pregnancy: used to evaluate fetal circulation and placenta

If the placenta is not functioning well

If the placenta, for all the functions we have seen, is essential for pregnancy, it is not surprising that if it forms or functions poorly there can be negative consequences for the pregnancy itself and for the health of the baby and sometimes of the mother.

Effects on pregnancy

Abnormalities and insufficiencies of the placenta are now considered to be the basis of the main pathologies of pregnancy, such as the restriction of fetal growth, in which the baby does not develop as it should and which can lead to death in utero, or preeclampsia, which is dangerous for both the mother. , both for the son.

The long-term effects

The way the placenta works affects not only the "here and now" of pregnancy, but also the long-term health of the baby and the adult to come. The first to realize this, about twenty years ago, was the English epidemiologist David Barker: he had in fact observed that children born with a weight of less than 2500 grams (in general a sign of not very efficient placental functioning) ran, as adults, a greater risk of cardiovascular disease.

It is the so-called theory of the fetal origin of diseases, according to which the conditions of life in utero - which depend very much on the efficiency of the placenta - influence the risk of developing hypertension, diabetes, some types of cancer and even psychiatric and cognitive disorders as adults.

Factors that can adversely affect the development and functioning of the placenta

They are different:

  • diabetes in pregnancy
  • maternal obesity
  • smoking habit
  • alcohol abuse
  • maternal genetic predisposition
  • air or food pollution (for this reason, mothers-to-be are advised to consume small fish such as blue fish and not large fish, such as tuna, which tend to accumulate mercury)
  • psychosocial stress (through a hormonal action that causes an increase in the general inflammatory state)
Read also: The first thousand days of the child
  • the placenta
  • anterior placenta
  • previous placenta
  • placenta accreta
  • placental abruption in pregnancy

Questions and answers

When does the placenta start to work?

The sketch of the placenta begins to form during the first cell divisions of the zygote. With the implantation of the embryo in the uterine mucosa it begins to perform its functions: we are in the very early stages of pregnancy.

What happens if the placenta detaches?

Detachment of the placenta during pregnancy (particularly after 20 weeks) is a complication in which the placenta becomes completely or partially detached from the uterus. If the detachment is minimal there are practically no consequences, while if it is extensive it can lead to restrictions in fetal growth or even death in utero.

  • placenta
  • development of the fetus
  • preeclampsia
  • growth retardation
  • diabetes in pregnancy
  • weeks 1-13
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