When Does the Placenta Take Over

Hormone Production and Relief From Morning Sickness

There is nothing quite like standing in front of a room full of colleagues to do a presentation, only to puke into a wastebasket mid-sentence. If you struggle with morning sickness, chances are good that someone has tried to comfort you by telling you that you will "feel better when your placenta takes over." It's hard to be patient when you want to feel better, especially if you have other children who want attention from mommy. However, as the placenta develops, most women do naturally find relief and feel better.

What the Placenta Does

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The placenta is an endocrine organ that begins to develop after implantation of the embryo in the uterus. It provides oxygen and nutrients to your growing baby through the umbilical cord. The placenta also filters out waste and toxins from the baby's blood and is responsible for the production of several hormones, including the progesterone necessary for sustaining your pregnancy.

When the Placenta Takes Over

In the beginning of your pregnancy, the corpus luteum forms from the ovarian follicle that released your egg, and it produces progesterone to support pregnancy while the placenta develops. During this time, women are 70 to 80 percent more likely to experience the nausea and vomiting of morning sickness, which is relieved only when the placenta develops enough to take over production of progesterone. This normally happens from 8 to 13 weeks, or by the end of the first trimester. Once the placenta takes over, the corpus luteum reduces in size until it finally resolves, by 20 weeks at the latest. During the second trimester, the fully functioning placenta and resulting departure of the corpus luteum and morning sickness grant most women a much-appreciated burst of energy that's not experienced at any other time during pregnancy. The second trimester is the ideal time to set up the nursery or get ahead of projects at work before the baby comes.

What to Expect

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Expect normal pregnancy nausea and vomiting to continue at least through your eighth week of pregnancy and to gradually decrease over the next few weeks, as the placenta increases production of progesterone and the corpus luteum gradually dies off. Don't expect overnight relief, but know that morning sickness does not last forever, and gradual improvement provides welcome relief.

When to See a Doctor or Midwife

Make sure to see your doctor or midwife when you have concerns about your body, pregnancy and baby. If you're having trouble keeping down food or fluids, you could have a more severe form of morning sickness that can be treated with medication, fluids or lifestyle changes. If you experience spotting or cramping, your doctor or midwife can check your body and baby, as well as make sure the placenta is developing properly. If you're concerned, ask your doctor or midwife to rule out placenta previa, placenta accreta or placental abruption. Usually, a detailed ultrasound will show the vessels of your placenta and uterus functioning normally and put your mind at ease. Sometimes, your doctor or midwife will recommend bed rest, hospitalization or a change in birth plans.