Some boost your metabolism to help supply energy to both you and your growing baby. The placenta starts developing very early on in pregnancy at about week 4. Seven or eight days after a sperm fertilizes an egg, a mass of cells — the earliest form of an embryo — implants into the wall of the uterus.
Some cells from this mass split away, burrowing deeper into the uterine wall. Over the next two months, the placenta develops. Small capillaries turn into larger vessels, providing your growing baby with more oxygen and nutrients.
As you near the second trimester, the placenta will have completed its Herculean development. Between weeks 10 to 12 of pregnancy, your placenta takes over from a structure known as the corpus luteum. It'll sustain your baby for the rest of pregnancy — and continue to grow larger as your baby grows. The corpus luteum is a collection of cells that produces progesterone and some estrogen.
It forms every month after you ovulate in the follicle that released the egg during that cycle. When you are pregnant, the structure continues to grow and produce hormones to support your little embryo until the placenta takes over. Forming a brand-new organ takes loads of energy and contributes significantly to first trimester pregnancy fatigue. In most pregnancies, the placenta is located in the upper part of the uterus.
Sometimes, however, the placenta attaches lower in the uterus or on the front uterine wall more on that in a second. Keep in mind, the placenta is a completely separate organ from your baby formed with the sole purpose of supporting your pregnancy. How much your placenta weighs depends on how far along you are in your pregnancy.
At 10 to 12 weeks of pregnancy, the average placenta weighs nearly 2 ounces. By 18 to 20 weeks, the placenta weighs about 5 ounces. At the same time, the heart is forming as a simple tube-like structure. The embryo already has some of its own blood vessels and blood begins to circulate.
A string of these blood vessels connects you to the embryo, and will become the umbilical cord. Read our cookies policy to find out more about our cookies and how we use them. At 6 to 7 weeks, the embryo develops a large bulge where the heart is and a bump at the head end of the neural tube.
This bump will become the brain and head. The embryo is curved and has a tail — it looks a bit like a small tadpole. The developing arms and legs become visible as small swellings limb buds. Little dimples on the side of the head will become the ears, and there are thickenings where the eyes will be.
The embryo has a thin layer of see-through skin. By the end of week 6, the embryo is about the size of a lentil. By 7 weeks, the embryo has grown to about 10mm long from head to bottom. This measurement is called the crown-rump length. The brain is growing rapidly and this results in the head growing faster than the rest of the body. The embryo has a large forehead, and the eyes and ears continue to develop. The inner ear starts to develop, but the outer ear on the side of the head won't appear for a couple more weeks.
The limb buds start to form cartilage, which will develop into the bones of the legs and arms. The arm buds get longer and the ends flatten out — these will become the hands. Nerve cells continue to multiply and develop. The brain and spinal cord the nervous system starts to take shape. Some women believe that encapsulating and eating the placenta after birth helps them recover faster, though there's no scientific evidence to support this claim. Also note that there are potential risks associated with consuming the placenta, including infection and heavy metal contamination.
Be sure to discuss this topic with your provider if it's something you're considering. Get vaccinated. Some viruses can cross the placenta. Rubella , for example, can cause serious birth defects if you become infected during pregnancy. That's why it's important to make sure all of your vaccines are up to date before you get pregnant. BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organizations, professional groups of doctors and other experts, and published studies in peer-reviewed journals.
We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies.
Merck Manual. Stages of Development of the Fetus. Marijuana use during pregnancy and lactation. American College of Obstetricians and Gynecologists. Placental structure, function and drug transfer. Hayes EH. Consumption of the placenta in the postpartum period. Journal of Obstetric, Gynecologic, and Neonatal Nursing 45 1 Philadelphia, PA: Elsevier. Clinical practice guideline for the management of women who report decreased fetal movements.
Vaccinations for pregnant women. Yetter JF. Examination of the placenta. American Family Physician 57 5 In weeks 4 to 5 of early pregnancy, the embryo grows and develops within the lining of your womb.
The inner cells form into 2, and then later into 3 layers. Each of these layers will grow to be different parts of your baby's body:. In these early weeks of pregnancy, the embryo is attached to a tiny yolk sac that provides nourishment. A few weeks later, the placenta will be fully formed and take over the transfer of nutrients to the embryo.
The embryo is surrounded by fluid inside the amniotic sac. It's the outer layer of this sac that develops into the placenta.
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