The main function of the placenta is allow metabolic and gaseous exchanges between fetal and maternal blood. However, it is not the only function it has, as we will see in this article. It is also important to know that the position of the placenta, although it does not usually affect childbirth, it does in some specific cases, one of which we will talk about today, which is previa or low placenta.
The fetus and the placenta are connected to each other through the umbilical cord while the maternal organism communicates directly with the placenta through blood-filled sacs called blood lacunae.
What is the placenta?
It is a deciduous organ, therefore temporary, that forms in the uterus during pregnancy. The placenta is responsible for nourishing, protecting and assisting in fetal growth.
It is common to the pregnant woman and the fetus. One part is of maternal origin (made up of the modified or deciduous uterine endometrium), while the rest is of fetal origin (made up of chorionic villi). The placenta, therefore, represents the roots of the fetus in the mother's soil.
Functions of the placenta
As we have commented, the placenta serves as metabolic and gaseous exchanges between fetal and maternal blood, but not only that, it also performs many other functions, among which I will mention the most important:
- 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 fluids body parts of the fetus;
- contributes to the fetus necessary nutrients, including glucose, triglycerides, proteins, water, vitamins and mineral salts thanks to its permeability with respect to these nutrients present in maternal blood;
- allows the passage of antibodies by 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, although some can still pass through it, constituting a danger to the baby (caffeine, alcohol, nicotine, some medicines, drugs...);
- produces the hormonal substances necessary for pregnancy: human chorionic gonadotropin (HCG), progesterone, estrogen and prolactin.
In what position is the placenta?
The position of the placenta depends on the point of implantation of the embryo in the endometrium, therefore it can be anterior, posterior or lateral and this does not affect the pregnancy or delivery. However, it may happen that it is located lower than normal: in this case we are talking about low placenta or previa. About 5% of early pregnancies have a low placenta, which in most cases returns to its normal position as the pregnancy progresses. This happens because the uterus, when increasing in size, pushes it up. To correctly diagnose this situation, its location should be verified around the 35-36 week of gestation.
Generally, this requires the cesarean birth, especially in cases of central placenta previa. In this case, an obstruction of the cervix occurs that prevents the passage of the fetus through the birth canal.
Placenta previa and natural childbirth
Un attempted natural birth in these conditions it would cause lacerations in the placenta which in turn could lead to serious bleeding that could seriously endanger the health of the mother and the baby. To assess the functionality of the placenta under normal conditions, the most reliable parameter is above all that of fetal growth: if the size of the fetus corresponds to that expected based on gestational age and the amount of amniotic fluid is normal, it means that it is functioning well. . Other parameters that are evaluated through ultrasound examinations are uroflowmetry of the umbilical artery, which assesses the functionality of the placenta based on the conditions of the fetus, and uroflowmetry of the uterine arteries, which instead explores the maternal side. .