When Does the Placenta Form?


What is Placenta? A baby in the womb develops from a tiny mass of cells to a full-sized baby, and it goes through various development stages during this period. It starts with the fertilization of the egg that eventually develops into an embryo. Afterward, embryo changes to the fetus with the placenta. It is an organ that helps in providing the fetus with oxygen and other essential nutrients. It also helps in providing a route so that the waste products from the fetus can be drained.


Every mother is concerned about the wellbeing of the baby during all the development stages including the first week, second week, 8th and the 36th week. During all the process, the most obvious question that a pregnant woman asks is “When Does the Placenta Form?”

When Does the Placenta Form?

About the 3rd week of the pregnancy, the follicle collapses and produces progesterone hormone. This provides some nutrient supplies for the embryo during the trimester of the pregnancy. The embryo starts to develop and begins implementing itself on the wall of the womb around the 4th week of the pregnancy. Now, the embryo is in the form of a mass of cells, but not all of the cells are going to produce the body parts of the baby. Some cells turn to an organ that shaped as a disk is called placenta and it forms during the 2nd trimester. This organ or placenta is full of blood vessels. The placenta develops and grows on the upper part of the uterus but sometimes it develops on the below part of the uterus as well. In the case of fraternal twins, each baby gets their placenta in the case of identical twins, they may get a single placenta or two different placenta depending upon the time of the splitting of the eggs after fertilization.

From the starting of its development in the 4th week, the placenta keeps developing over the next couple of months. During this phase, the small capillaries turn to the blood vessel and provides nutrition and oxygen to the baby. The placenta keeps growing with your baby and in about 12th week, it becomes developed enough to replace the corpus luteum. The placenta weighs almost a pound when you are in your 40th week of pregnancy.

Why Is the Placenta So Important?

Once you are aware of the time when the placenta forms, the next thing that you may wonder is “What makes the Placenta so important?” Well, there are several reasons. In a simple way, it can be said that the Placenta plays a crucial role in the nutrition of the fetus. There are many other reasons, and these are described below:

Transfer of Gas

This is probably the most important job of the placenta for the development of the baby. It helps the required oxygen to come in and the carbon dioxide to goes out and mix it with the mother’s blood. The fetal blood vessel is responsible for the supply of the oxygen and a microscopic structure called villi contains many of these vessels. The placenta helps the oxygen of the blood of the mother to move to the fetal vessels and releases the carbon dioxides from the vessels to the mother’s blood system. So, Placenta is the medium of exchange of gas, and thus, it is impossible to transfer gas without it.

Supplies and produces Nutrition

The placenta works as the supplier of the nutrition to the fetus for the development of the baby before birth. It is capable of producing some vital nutrients such as the fats and carbohydrates. In the later stage, when the fetus starts growing, the placenta takes nutrient from the mother’s blood including protein, blood sugar, water, etc.

Hormone production

The placenta produces many important hormones that have an immense influence on the growth of the baby and the mother’s response to the pregnancy. It produces hormones like estrogen, progesterone, lactogen and growth hormone.

Provides protection against infections

The placenta is not only a supplier of nutrition but also acts as a protector against many infections. It protects the fetus and builds a defense system. It protects the fetus by transferring antibodies from the mother’s blood to the blood of the baby. Gamma globulin is a kind of antibody that moves easily to the fetus and gives the fetus a robust immunity and help I to fight against some specific infections.

Can there be any problems with the Placenta during Pregnancy and what are the causes?

There can be many complications that may arise during the pregnancy regarding the placenta, and it is a good idea to know about these facts and be prepared so that you may encounter these problems when needed.

Placental abruption

This is a condition when placenta peels away from the wall of the womb and can lead to cramps, vaginal bleeding, and excessive pain.

Placenta previa

Placenta previa is a condition when the placenta covers the cervix partially or entirely, and it effects in early pregnancy. This issue can be resolved by on its own when the uterus grows but may cause massive bleeding during pregnancy.

Placenta accrete

When the blood vessels of the placenta develop more than normal into the uterine wall, it causes excessive bleeding after delivery.

Retained placenta

It is a case when a placenta stays inside after the birth of the baby, and this may happen if the placenta traps in the cervix. This may result in infection and a lot of blood loss which may be a life-threatening condition.

As discussed above, the placenta is imperative for the growth of the baby and is an integral part of your pregnancy. It is advised to consult your doctor regularly during pregnancy to avoid any health hazard.

What is the role of the placenta after delivery?

Once you deliver the baby, it is essential to deliver the placenta as well. It is important to cut it off as it is not required in your body anymore. A fresh placenta will grow with the new pregnancy.