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Fertility Center

What Does Progesterone Do In Pregnancy?

What is the role of Progesterone in pregnancy?

  • Progesterone is known as the “pregnancy hormone.”
  • Progesterone helps the fertilized egg be implanted in the uterus to establish a pregnancy and help maintain a healthy pregnancy.
  • Women naturally produce progesterone in the ovaries, the placenta, and the adrenal glands during pregnancy.
  • During fertility treatments such as IVF (in vitro fertilization), progesterone is often given because the medications used in the process reduce a woman’s natural production of the hormone.

Progesterone is sometimes referred to as P4 or Prog, but is known as the “pregnancy hormone.” Progesterone is a hormone created early in pregnancy by a cyst on the ovary called the Corpus Luteum. This cyst of the ovarian follicles continues to produce progesterone for 10 weeks during pregnancy. After those initial weeks, then the placenta takes over producing progesterone. During the first trimester, progesterone levels rise exponentially, but plateau shortly after. Progesterone is key to creating a perfect environment for the ovaries to harbor the fetus by keeping the uterus muscle relaxed and helping the immune system tolerate foreign DNA. When a woman undergoes IVF or another fertility treatment, this hormone will sometimes need to be supplemented. Women’s ovarian follicles might also be poorly developed and may not secrete enough progesterone on their own. In these circumstances, progesterone will need to be supplemented as well.

Before Pregnancy: Progesterone helps the uterus be prepared for pregnancy

The hormone progesterone is secreted during early pregnancy and prepares the uterus for pregnancy. It causes the luteal phase to start and transforms the endometrium (uterine lining) by thickening it to receive an embryo. The embryo is the result of the female’s egg when it’s fertilized by the male’s sperm. When pursuing pregnancy, the fertilized embryo will reach the uterus normally 5 days after ovulation. Then two days later, it will attach to the uterine wall. After it attaches to the uterine wall, this is when progesterone levels peak. If undergoing IVF, the client would normally go through progesterone supplementation to help encourage the fertilized embryo to attach to the uterine wall.

During pregnancy: Progesterone helps support the fetus as it grows

When a woman is pregnant they produce hCG (human chorionic gonadotropin hormone). This is a signal to the ovaries to continue to produce progesterone. hCG prevents the onset of her menses (the blood and matter discharged during ovulation) and enables a woman to become pregnant. Progesterone then continues to be produced, nurturing the fetus as it starts to grow. After 8-10 weeks of pregnancy, the placenta takes over progesterone production and increases production until the baby is born.

Benefits of Progesterone

Estrogen, the primary female sex hormone, stimulates the growth of tissue inside the uterus. To prevent uterine overgrowth, progesterone slows this activity and redirects growth elsewhere. Your fertility doctor will augment your natural production of progesterone to avoid early miscarriage and help maintain a healthy level of progesterone during pregnancy.

Other benefits include:

  • Stimulates bone growth, helping to protect from osteoporosis.
  • Helps maintain a healthy weight by burning body fat for energy.
  • Decreases craving for sweet and high-sugar foods, stabilizing blood sugar levels.
  • Is a diuretic, normalizing body fluid and salt levels.

Different forms of progesterone

Vaginal suppositories:

  • Widely used, but are not FDA-approved
  • Wax-based
  • Compounded by specialty pharmacists
  • Used up to 2-3 times a day
  • leakage can be messy

Vaginal gel:

  • This is the only once-daily FDA-approved progesterone for ART for up to 12 weeks of pregnancy
  • This is also the only FDA-approved progesterone for a replacement for donor egg recipients and donor egg transfers
  • It’s used once a day for progesterone supplementation
  • Some discharge reported during use

Vaginal inserts:

  • FDA-approved for progesterone supplementation but not for progesterone replacement
  • Effective in women under 35 years
  • used 2 to 3 times a day


  • Widely used; the oldest, most established method for progesterone delivery
  • injected into the buttocks once a day
  • Requires a long, thick needle to penetrate layers of fat and skin
  • Injections may be painful
  • Difficult to administer by yourself

Progesterone Side Effects During Pregnancy

In 1999, the FDA found that using synthetic progesterone may be associated with birth defects. Synthetic progesterone is primarily derived from the male hormone testosterone. Be very careful when undergoing progesterone treatments to make sure you’re not using synthetic progesterone. Always consult a doctor when considering taking progesterone during pregnancy.

Common side effects when using progesterone:

  • Drowsiness
  • Fluid retention or bloating
  • Hot flashes
  • Depression
  • Vaginal discharge.
  • Urinary problems
  • Dizziness
  • Abdominal pain or cramping
  • Headaches
  • Breast tenderness
  • Joint pain

Talking with your health care provider is important when deciding what supplementation is best for you. Progesterone supports implantation and pregnancy and is an important part of infertility treatment. Health care providers usually have a preference based on experience with other methods that can help you decide which supplementation is best for your infertility treatment.