Functions
During pregnancy, amniotic fluid envelops the product of conception, absorbing and dampening insults from the outside world, such as shocks and pressures of various kinds. Likewise, the amniotic fluid protects the surrounding tissues of the mother from the movements of the fetus, which are facilitated by her own presence. This fluid also acts as a thermal insulator and allows the optimal development of the various bodily structures of the fetus.
Amniotic cavity
In the very early stages of development, the amniotic fluid is secreted by the cells of the amnion; subsequently, throughout the first trimester of pregnancy, its accumulation is linked to the transudation of the maternal-fetal plasma that circulates in the interstitial spaces of the membranes.
Synthesis and Composition
In the second trimester and up to the twentieth week of pregnancy, the amniotic fluid has a composition and an osmolarity superimposable to those of the blood of the mother and fetus, whose skin is permeable to water, electrolytes, urea and creatinine .
After the twentieth week, the amniotic fluid begins to be integrated and progressively replaced by the urine of the fetus, thanks to the maturation of its renal emunctorium. From here until the end of gestation, the fetus will participate not only in the production of amniotic fluid, but also in the in fact, around the fifth month, he begins to swallow part of the liquid, absorbing it through the intestine (to the delight of urinotherapy supporters ...).
Did you know that ...The product of conception is defined:
- zygote - from fertilization to the end of the second week;
- embryo: from the third week to the end of the third month;
- fetus: from the fourth month to delivery.
During pregnancy, the fetus produces large quantities of sebum, necessary to form the so-called varnish, a lipid layer that protects its skin from maceration induced by amniotic fluid.
Once it has entered the bloodstream, through the umbilical cord and the placenta, the amniotic fluid reaches the maternal circulation, strengthening the bond between the two organisms. In the second half of pregnancy, the lungs and the umbilical cord also contribute to the synthesis of amniotic fluid, while a minimal contribution can also be attributed to the sweat glands, tears and gastrointestinal secretions.
During the first two trimesters of pregnancy the volume of amniotic fluid far exceeds that of the embryo, first, and then of the fetus, favoring its movement and symmetrical development. During the last three months of gestation the ratio between the two volumes decreases in favor of the fetal one.
Breaking of the waters
Towards the thirty-fourth week the amniotic fluid reaches the peak of its volume, around 800 ml which will be about 600 ml during labor. In this phase the amnion can tear suddenly or rupture only partially; in the first case the woman she feels the descent into the vagina of a hot liquid, which turns out to be odorless and colorless, while in the second the signals are less nuanced.
In both situations, however, it is a clear sign that the happy event is almost upon us.
Sometimes, especially in the presence of bacterial infections, the membranes can rupture before the 38th week of gestation; in these cases we speak of premature rupture of the membranes (PROM). Regardless of the period in which it occurs, after the breakdown of the water it is very important that the woman goes to the hospital to prevent the risk of infections.
To learn more, read: Breaking of the waters "
Amniocentesis
Inside the amniotic fluid there are various substances in suspension; as we have seen, these substances vary according to the stage of development of the product of conception.
Amniocentesis, that is to say the removal of amniotic fluid, is generally carried out between the sixteenth and eighteenth week of gestation. In this phase, within the amniotic fluid are found - among other things - cells of fetal origin, in particularly those of flaking of epithelial tissues (skin, lower urinary tract, trachea, etc.). The culture of these cells allows to examine the chromosomal map of the unborn child and thus formulate a prenatal diagnosis about the presence or absence of chromosomal abnormalities (such as the syndrome In addition, the dosage of alphafetoprotein in the amniotic fluid allows to investigate the possible presence of diseases and malformations, such as spina bifida, anencephaly or meningocele.
In amniocentesis, amniotic fluid is taken with a fine needle under ultrasound guidance. Like all invasive procedures, amniocentesis presents a certain percentage of risk of spontaneous abortion, quantifiable in about 0.5%. It is therefore useless to carry out this examination in the event that the parents exclude recourse to termination of pregnancy even in the presence of any serious abnormalities of the fetus.
Recent studies have found that amniotic fluid is an "excellent source of stem cells, multipotent and capable of differentiating into various tissues. These cells can be stored in special private facilities, the so-called stem cell banks, waiting for science to develop them. the large - but in many ways still potential - applications.
Changes in amniotic fluid
Polyhydramnios
An excessive amount of amniotic fluid is called polyhydramnios. This condition can be the consequence of a multiple pregnancy (twin or multiple), gestational diabetes or congenital abnormalities of the fetus (which lead to the inability to swallow or absorb, for example due to the presence of an "intestinal obstruction).
Oligodramnios
A small amount of amniotic fluid is referred to as oligohydramnios. In this case, the condition may depend on placental dysfunctions, rupture of the amnion, prolonged pregnancy beyond the canonical 40 weeks or congenital anomalies of the fetus (which lead to the inability to produce urine).
Other articles on "Amniotic Fluid"
- Amniocentesis
- Amniocentesis: to perform it or not to perform it
