The amniotic sac is a membrane lining that protects the embryo.
The amniotic sac is the membrane lining that develops on the eighth or ninth day after fertilization to cover the embryo. This sac is made up of the amnion (the inner membrane that contains the fetus and has amniotic fluid) and the chorion (the outer membrane that is part of the placenta and houses the amnion).
It should be noted that sac is a term that derives from saccus , a Latin concept. It is a container, receptacle or container that allows something to be contained inside. Amniotic , for its part, is that linked to the amnion (the bag that encloses an embryo).
Characteristics of the amniotic sac
Inside the amniotic sac, the fetus is protected, can move and is at a stable temperature. The amniotic fluid increases its volume inside the amnion as the fetus develops. This liquid is in circulation since the fetus inhales and swallows it but, in turn, also expels it.
It should be noted that, between the amnion and the chorion , the amniotic sac has a layer with a high amount of fibroblasts and collagen that enables the expansion of the sac. It is important to keep in mind that the amniotic sac is much larger in the ninth month of pregnancy, when the baby can weigh about three kilograms, than in the first weeks.
The amniotic sac is formed with the amnion and the chorion.
Liquid level
The fluid level within the amniotic sac must be maintained within certain parameters. When the amniotic sac has little fluid, what is known as oligohydramnios occurs. On the other hand, if the fluid inside the amniotic sac is excessive, it is called polyhydramnios . Let's look at these concepts in more detail below.
Oligohydramnios
As mentioned above, this is a phenomenon characterized by a shortage of amniotic fluid. This occurs in a percentage of pregnancies that does not reach 10%, especially during the first three months, although it can also occur towards the end.
Some of the causes are the consumption of ACEI drugs (angiotensin-converting enzyme inhibitors, used to combat heart failure, among other cardiovascular pathologies, such as high blood pressure), and it can occur in women who do not have risk factors. . Oligohydramnios normally appears as a consequence of certain anomalies in the fetal urinary tract, such as genitourinary obstruction.
To diagnose this disorder, an ultrasound is necessary (revealing an amniotic fluid index below 5) and treatment must be carried out by a specialized doctor. It is worth mentioning that not all health professionals are in favor of taking the presence of this disorder in the amniotic sac as a sign of gestational problems, and this continues to give rise to controversy.
Polyhydramnios
Unlike oligohydramnios, polyhydramnios indicates excess amniotic fluid (the index must be greater than 18). This disorder can appear as a result of the fetus not being able to ingest the normal amount of fluid, or due to complications in the stomach, intestine, brain, lungs or nervous system, among others.
Generally, the underlying causes associated with this phenomenon in the amniotic sac are the following:
- Anomalies in the abdomen of the fetus, such as esophageal atresia, normally linked to tracheal agenesis, tracheoesophageal fistula, intestinal atresia or duodenal atresia, among other problems.
- Multiple pregnancy in which fetofetal transfusion syndrome occurs, that is, the amount of amniotic fluid is greater in the recipient twin than in the donor.
- Deficiency of the hormone vasopressin, which is responsible for controlling water reabsorption through the concentration of urine.