The placenta is a temporary organ that attaches itself to the uterus and to the baby’s umbilical cord. It’s through the placenta that the growing fetus is able to get oxygen and nutrients from the mother.
Placenta is a Latin word meaning “flat cake.” By attaching itself to the baby’s umbilical cord, it provides the baby with nourishment and oxygen from the mother while also eliminating the baby’s waste.
But how does the placenta develop?
The placenta begins to grow upon the implantation of a structure known as the blastocyst. The blastocyst consists of a bunch of cells, referred to as inner cell mass, from which the embryo develops. There is also a cluster of outer cells, known as the trophoblast, from which the placenta forms.
The placenta develops wherever the fertilized egg embeds itself in your womb (or uterus):
- anterior position (on the front wall of your womb, closest to the belly)
- posterior position (on the back wall of your womb, closest to the spine)
- fundal position (on the top wall of your womb)
- lateral position (on the right or left side of your womb)
These are all normal places for the placenta to implant and grow.
When the placenta attaches itself to the back of the uterus, it is called a posterior placenta. When it attaches itself to the front of the uterus, it is known as an anterior placenta.
The moment the blastocyst attaches to the inner lining of the uterus (or endometrium), the placenta starts developing. The trophoblast grows quickly and its cells differentiate into two layers: cytotrophoblasts, which are the inner cells, and syncytiotrophoblasts, which are the outer cells.
As the trophoblast proliferates, newly formed cells move to the syncytiotrophoblast, creating a rapidly growing cell mass. The syncytiotrophoblast functions as the outer cover of the placenta throughout the entire pregnancy.
The cytotrophoblasts reshape the blood vessels in the uterus. It’s through these vessels that the placenta receives maternal blood. As cells continue to proliferate, the placenta gradually grows. By the time a woman gives birth, the placenta may weigh as much as 500 grams and measure nine inches in length.
The placenta undergoes numerous changes from conception till birth. So as the baby grows, the placenta morphs to accommodate their development. After delivery, the placenta is expelled by the uterus.
Although it may sound like Greek to many people, the term posterior placenta describes the placenta’s attachment to the back wall of the uterus.
If your doctor determines that you have a posterior placenta, rest assured that it is considered completely normal. In fact, the upper (or fundal) portion of the uterine back wall is one of the best locations for the baby to be in. It allows them to move into the anterior position just before birth.
Furthermore, a posterior placenta does not affect or interfere with the growth and development of the baby.
During pregnancy, the placenta location can change. This is why your doctor may perform an anomaly scan in the second trimester of pregnancy (at roughly 18 to 21 weeks). Another scan may be necessary in the third trimester to double-check placenta positioning prior to delivery.
One placental location that might be problematic is when the placenta grows towards the cervix. This is called placenta previa. In this position, the placenta could detach from the uterine wall and cause premature labor or internal bleeding.
Another potentially serious condition, known as placenta accreta, happens when parts of the placenta attach too deeply into the uterine wall. Instead of completely detaching itself after delivery, some or all of the placenta remains in the uterus, sometimes resulting in massive bleeding.
In such cases, the doctor may recommend a caesarian section and a post-delivery hysterectomy.
In some instances, the placenta remains in the womb after the baby has been delivered. This is called a retained placenta, and when left untreated, it can also lead to certain complications.
To recap, a posterior placenta is one that attaches itself to the back of the uterus, while an anterior placenta attaches itself to the front. Both placental positions are considered normal. Aside from being an ideal location for delivery, the other benefit of a posterior placenta is being able to feel your baby’s movements early on.
This is not the case with an anterior placenta because the placenta may create a space between the baby and your abdomen. Otherwise, there should not be any problems or complications with anterior positioning.
Neither posterior or anterior placental location will affect the development or growth of a strong and healthy baby.