Introduction
The placenta is a temporary organ that is formed during the pregnancy period in the uterus of the woman. It is attached to the uterus wall temporarily during pregnancy and is the medium through which babies get their nutrition from the mother. In the womb, the placenta provides oxygen and nutrients to the baby and removes harmful waste and carbon dioxide from the baby's body.
What Are the Functions of the Placenta During Pregnancy?
The placenta plays an important role in connecting the mother to the baby. Some of its functions are:
- Implantation: It helps the fertilized egg formed to get implanted directly by invading the wall of the uterus.
- Human Chorionic Gonadotropin (HCG): It helps to synthesize the human chorionic gonadotropin hormone from the fertilized implanted egg, which provides an indication to the mother about the pregnancy while performing urine pregnancy tests.
- Nutrient and Gas Exchange: Villis (grape-like structure) in the placenta provide gas exchanges between mother and baby and provide nutrients to the baby from the mother.
- Protection of the Baby: It protects the baby from any infection or immunologic attack.
- Development of the Baby: Placental growth factors are required to promote fetal development and maturity; hence they help in the baby's development.
How Does the Placenta Develop?
Two portions form the placenta, one being the fetal portion called the chorion and the other a maternal portion called decidua basalis. The uterus and placenta form an utero-circulatory system for blood circulation of the maternal-fetal exchanges. As the pregnancy progresses, the villi also start disappearing. So, nearly five types of villi form a placenta, mesenchyme villi, immature intermediate villi, stem villi, mature intermediate villi, and terminal villi. Three to five mature intermediate villi arise from mesenchyme, and ten to twelve terminal villi arise from the mature intermediate and form a communication between the chorionic plate of the fetal portion and the decidua basalis portion of the maternal portion. Some villi remain free in space, while others provide structural stability for the placenta. There is a presence of a placental barrier that separates the mother's blood from the baby's blood.
What Is the Physiology of the Placenta?
1. Macroscopic Physiology: The placenta can form anywhere in the uterus. It can be the placenta's anterior, posterior, lateral, or fundal positions.
2. Microscopic Physiology: There are differences in the microscopic levels also. There are different layers of cells between the fetal chorion and the uterus lining of the mother. There are a number of epithelial layers and basal laminae on both the fetal and maternal layers and below the basal lamina are connective tissues and blood vessels.
3. Exchange: The antibodies can also cross the placenta from the mother to the fetus, and this provides immunity against various infections to the fetus from the mother as passive immunity. The placenta also exchanges nutrients from mother to fetus by simple diffusion, active transport, or complex diffusion.
4. Placental Blood Supply and Drainage:
- Umbilical Arteries - Umbilical arteries (blood vessels) arise from iliac arteries. It carries deoxygenated blood from the fetus to the placenta.
- Umbilical Veins - Umbilical veins carry oxygenated blood from the placenta to the fetus.
- Shunts - There are three main shunts; ductus venosus, foramen ovale, and ductus arteriosus. They supply oxygen and nutrients to the organs of the fetus.
What Could Be the Pathologies Related to Placenta?
- Intrauterine Growth Restriction (IUGR): It occurs when fetal growth is less than the expected weight during the specific gestation period or week. It can be less than the tenth percentile of the expected or predicted weight in that pregnancy week. It can be fatal to the fetus and lead to fetal mortality. If the fetus is not growing, it can be due to maternal, fetal, or placental causes. It can cause retardation of the fetus, with chromosomal defects, congenital malformations, and infections. All these retardations occur when the blood flow to the fetus gets compromised.
- Choriocarcinoma: Choriocarcinoma is a tumor of the placental tissues. The placental tissues in the absence of villi, can develop into a small tumor affecting the mother's blood circulation. Pregnant women with uterus larger than the expected size and age have a chance of developing these tumors. It is evaluated by snowstorm appearance.
- Preeclampsia: Preeclampsia (a condition developed in the 20th week of gestation due to high blood pressure of pregnant women) is usually seen in the third trimester of pregnancy. The leading cause of preeclampsia is hypertension of the mother.
- Placenta Previa: Placenta previa is a condition in which the placenta implants on the cervical region. Placenta previa is accompanied by vaginal bleeding, usually in the third trimester. The implantation is diagnosed by transvaginal and transabdominal ultrasound.
- Placental Abruption: Placental abruption is the case of early separation of the placenta. The separation can be complete to part from the decidua basalis. It is the leading cause of vaginal bleeding in the later stages of pregnancy. Ideally, the bleeding is due to rupturing the mother's blood vessels, but the placental separation can also cause it. Ultrasound is ideally recommended to diagnose placental abruptions. It can be dangerous as it can cause stillbirth.
- Placenta Accreta: Placenta accreta occurs due to deep attachment of the placenta in the lining of the uterus. It results in improper separation or attachment of the placenta from the endometrium layer of the uterus. Patients with C-sections (cesarean sections), uterine surgery, or multiparity have a risk of it. It can cause difficulty with placental separation and postpartum bleeding. MRI (magnetic resonance imaging) can be performed to diagnose it.
- Retained Placenta: When the placenta remains inside the uterus, it is called the retained placenta.
- Placenta Insufficiency - When the placenta is not providing adequate nutrients as required by the fetus, then a condition called placental insufficiency forms.
Conclusion
The placenta is the temporary organ that develops during pregnancy to nourish the baby in the womb of the mother. It has many roles, like oxygen supply and nutrient supply to the fetus. However, they develop certain placental pathologies like placental abruption, retained placenta, placenta accreta, and previa which can be monitored using various diagnostic procedures, and the complications can be prevented to improve the lifespan of the fetus and the living condition of the mother.
