How is the accessory placenta formed?

The placenta is not the place where the baby rests in the mother's belly, but the place where the baby absorbs nutrients in the mother's belly. Only when the placenta develops healthily can the baby absorb more nutrients and grow healthier. The accessory placenta is not the twins we imagine, but another placenta that grows next to the main placenta. Generally speaking, there is only one placenta, so why does a secondary placenta appear?

A pregnant woman's accessory placenta refers to one or several placental lobules that develop within the fetal membrane at a certain distance from the main placenta. The accessory placenta is connected to the main placenta by blood vessels derived from the fetus. Many people are curious about the reasons for the formation of the accessory placenta. Below, the editor of Xuexi.la will introduce you to the relevant knowledge about accessory placenta.

Causes of placenta in pregnant women

The mechanism of occurrence is still unclear. It is believed that endometrial dysplasia or endometrial inflammation, poor nutritional conditions or blood supply at the site of blastocyst attachment, prompting the placenta to find a better decidua site and placenta migration, thus forming an accessory placenta.

Clinical manifestations of accessory placenta in pregnant women

If accessory placenta is not diagnosed before delivery and is not carefully examined after delivery, it can easily lead to retained accessory placenta and severe postpartum hemorrhage.

Ultrasound of the accessory placenta in pregnant women

Scan

The placenta is located by scanning the uterine wall with a series of longitudinal and transverse sections. If placental echoes are found outside the main placenta, multiple sections should be taken to show the relationship between the two. Only after confirming that there is no connection between the two can a diagnosis be made.

Performance

(1) Two-dimensional ultrasound shows that there are one or more solid masses with the same echo as the placenta outside the main placenta, which are at least 2 cm away from the main placenta.

(2) Color Doppler blood flow imaging showed that there were blood vessels connecting this solid mass to the main placenta, and the vascular Doppler spectrum indicated that it was a fetal blood vessel.

(3) If the accessory placenta extends from the primary placenta across the internal cervical os to the opposite side, attention should be paid to whether there is vasa previa.

Function of the placenta in pregnant women

The function of the placenta is complex and is not simply filtration. The site for substance exchange in the placenta is mainly at the vascular syncytial membrane (VSM). The vascular syncytial membrane is a thin film composed of five layers: syncytiotrophoblast cells, syncytiotrophoblast basement membrane, villous stroma, capillary basement membrane and capillary endothelial cells.

There are two independent circulatory systems in the placenta, one for the fetus and the other for the mother (even if it develops to the sinusoidal endothelial type, such as in the late rabbit embryo, there is still a layer of endothelial cells separating the two sides). The chorionic villi can be regarded as a semipermeable membrane. The area of ​​contact between the entire chorionic villi and the maternal blood is 7 to 14 square meters. When the maternal blood flows in the gaps between the villi and the fetal blood flows in the villi, substances can be exchanged.

It is generally believed that oxygen, carbon dioxide and many small molecules rely on diffusion and osmosis for the placenta, while large molecules such as proteins, antibodies, hormones, etc. rely on active transport and drink transport. Some larger molecules (such as Rh positive antigens, etc.) generally cannot be transported; however, in cases of hypoxia, trauma, and special delivery, cross-flow and mixing may occur. During normal pregnancy, maternal blood and fetal blood are separated and do not interfere with each other, while selectively exchanging substances. This phenomenon is called the placental barrier. The composition of the barrier includes the endothelial cells of the microvessels in the villus core, the basement membrane, connective tissue, epithelial basement membrane and chorionic epithelium, which are all daughter tissues in the case of a sinusoidal villus placenta. Other types of placentas include maternal tissues, such as endometrial epithelium, basement membrane, connective tissue, and endothelium.

The placenta also has a storage function. For example, in the early stages of pregnancy, the placenta grows very quickly. A large amount of nutrients (protein, glycogen, calcium, iron, etc.) are stored in the placental cells to meet the needs of fetal growth. The placenta has a function equivalent to that of the liver. It not only stores nutrients but also has a regulatory effect. In the later stages of development, the fetal liver gradually grows and develops fully, and the metabolic regulatory function of the placenta gradually decreases and even disappears. The placenta can also transform and synthesize some substances, perform multiple functions of the digestive tract, lungs, kidneys, liver and endocrine glands, and regulate these functions to protect the fetus and mother so that the pregnancy proceeds smoothly.