When Does The Placenta Form? And, Like, What Does It

Pregnant woman looking at her baby sonographySouth_agency/Getty Images

When it comes to pregnancy, the placenta is kind of a big deal. After all, it’s a whole new organ your pregnant body grows right along with your little one to serve as a sort of one-stop-shop for your baby’s needs. But even if you know the basics about this physiological marvel, you probably have other questions. When does the placenta form? And, like, what exactly does it do?

Throughout your pregnancy, your obstetrician or health care provider will keep tabs on both your baby and placenta — because the two are invariably linked. So, to give you a better grasp of this new and vital pregnancy organ, we’re here with a crash course on placental development.

What is the placenta?

The placenta is a temporary organ that develops in your uterus during pregnancy. According to the Mayo Clinic, it “provides oxygen and nutrients to your growing baby and removes waste products from your baby’s food.” So, essentially, it’s a lifeline between your growing baby and your blood supply.

A fetomaternal organ, it functions with two components: fetal placenta (chorion frondosum) and maternal placenta (decidua basalis). These develop from the same blastocysts that form the baby and maternal uterine tissue, respectively.

When does the placenta form?

To understand when the placenta forms, you have to take a look at the whole journey. So, here’s a quick refresher. When you ovulate, an egg leaves the ovary and heads through your fallopian tube. The hope? That it’ll get fertilized. If that does happen, the egg (called a zygote) and a spermatozoid will begin forming the fetus. While in the fallopian tube, the zygote completes cell divisions — which continue when it reaches the uterus. At that point, it becomes a blastocyst. Some of these cells start to form the placenta while others go toward forming the fetus, with the blastocyst embedding in the endometrium (a process known as implantation).

By the end of the 8th week of fertilization, or around 10 weeks pregnant, the embryo is considered a fetus. The placenta has formed and started to grow and develop. By 18 to 20 weeks, the placenta is fully formed but continues to grow throughout your pregnancy. By 34 weeks pregnant, the placenta is officially considered “mature.”

When does the placenta take over?

The placenta obviously boasts some important roles, such as hormone production and delivering nutrients to your little nugget. Curious when it takes over to do these things? Well, every woman and every pregnancy is different, so there’s no absolute rule. However, the placenta typically takes over between 8 to 12 weeks pregnant. The average time is around 10 weeks.

What are some possible placental complications?

If all goes according to plan, the placenta attaches to the wall of your uterus and grows right along with it. Unfortunately, things can go awry. Here are a few possible placenta disorders:

  • Placenta previa: When the placenta grows in the lowest part of the womb, covering all or part of the cervix.
  • Placental abruption: When the placenta detaches from the wall of the uterus.
  • Placenta accreta: When all or part of the placenta embeds too deep into the uterine wall.
  • Calcified placenta: When small calcium deposits build up on the placenta.
  • Anterior placenta: When the placenta attaches to the front of the stomach (which, for the record, isn’t so much a problem as a variation of placental development).
  • Placental insufficiency: When the placenta can’t deliver an adequate supply of oxygen and nutrients to the fetus, a condition that requires monitoring.

Throughout your pregnancy, your obstetrician will be checking on the health and positioning of your placenta. They’ll alert you to any potential issues as soon as possible so you can determine the best course of treatment together.