The placenta is a temporary organ that develops in the uterus during pregnancy, forming a connection between the pregnant individual and the growing fetus. It facilitates exchanges between the two, providing oxygen and nutrients to the developing baby. This organ also efficiently removes waste products, such as carbon dioxide, from the fetal bloodstream. The placenta begins to form shortly after a fertilized egg implants into the uterine wall, around seven to ten days after conception.
The Placenta During Pregnancy
During pregnancy, the placenta is often first observed through ultrasound imaging, appearing as a thickened, disc-shaped structure attached to the uterine wall. Its appearance is uniformly echogenic, meaning it reflects sound waves consistently. Sonographers assess its location, which can vary, commonly being anterior (towards the front of the uterus), posterior (towards the back), or fundal (at the top of the uterus).
The placenta’s thickness increases with gestational age. A hypoechoic band, an area that appears darker on the ultrasound, is seen behind the placenta, separating it from the uterine muscle. This imaging allows healthcare providers to monitor the placenta’s development and position throughout gestation.
The Placenta After Birth
Following birth, the placenta is delivered within 30 minutes and is a substantial organ. At term, it weighs approximately 500 grams (just over 1 pound) and measures about 22 centimeters (9 inches) in diameter, with a thickness of 2 to 2.5 centimeters at its center. This organ has two distinct surfaces that reveal its former connection points.
The fetal side is smooth and shiny, showcasing branching blood vessels that emanate from the umbilical cord insertion point. This network of vessels is informally called the “Tree of Life.” In contrast, the maternal side has a rough, dark reddish-blue, and spongy appearance, marked by distinct lobes or cotyledons. Healthcare providers examine this side carefully to ensure no pieces remain within the uterus, which could lead to complications.
Understanding Placenta Anatomy
The placenta is composed of both fetal and maternal tissues, working in concert. The umbilical cord, a tube containing two arteries and one vein, connects the fetus directly to the placenta, serving as the pathway for nutrient and waste exchange. The fetal surface of the placenta is known as the chorionic plate, covered by the amnion, a membrane that gives it a shiny look.
The maternal side of the placenta includes the basal plate, which is derived from the uterine lining. Within the placenta, fetal blood vessels are contained in structures called villi, which are bathed in maternal blood within the intervillous space, allowing for the transfer of substances without direct blood mixing. This design supports the developing fetus throughout pregnancy.