Progesterone is known as the “pregnancy hormone.” Without enough progesterone, a woman’s body can’t continue to grow a fertilized egg.

If you’re attempting to become pregnant, your doctor may recommend progesterone treatments. They can help support your pregnancy. They may also recommend them if you’ve miscarried in the past or need hormonal support during in vitro fertilization (IVF) and other fertility treatments.

One option is Prometrium. This medication is a form of progesterone. It’s FDA-approved in pill form, but some doctors will recommend that a woman use it vaginally.

Progesterone helps you achieve and maintain pregnancy. During the second half of your menstrual cycle, your progesterone levels go up.

The hormone helps thicken the lining of your uterus. As a result, the lining is better able to support the implantation of a fertilized egg. If the lining is too thin, implantation can’t occur.

When a woman becomes pregnant, her corpus luteum (empty egg follicle) makes progesterone during early pregnancy. This continues until the placenta takes over. High levels of progesterone help to keep ovulation from occurring. It also helps grow milk-producing glands.

After weeks 8 to 10 of pregnancy, a woman’s placenta starts to produce progesterone. This means progesterone therapy is often a short-term option for reducing her miscarriage risk.

Because progesterone is crucial for pregnancy, low progesterone is also associated with miscarriage. While it’s not the single cause of miscarriage, studies point to the idea that progesterone could play a role.

According to the World Health Organization, doctors in Vietnam, France, and Italy often prescribe progesterone as a way to prevent miscarriage.

Prometrium is a brand name for hormones known as progestins. Prometrium is a bioidentical hormone. This means it’s chemically similar to the kind of progesterone a woman naturally produces.

Prometrium is derived from yams. While it’s traditionally available in pill form, some doctors may prescribe it off-label for insertion into the vagina. The FDA hasn’t currently approved the medication for vaginal use.

According to the National Infertility Association, using the medication vaginally is associated with fewer side effects than taking it orally.

A doctor may prescribe Prometrium vaginally as a way to increase a woman’s natural progesterone in the hopes of maintaining pregnancy.

There isn’t specific research on Prometrium and miscarriage, but there’s research on the benefits of vaginal progesterone.

A study published in Ultrasound in Obstetrics & Gynecology found that pregnant women in their second trimester with a short cervix who used vaginal progesterone gel were less likely to experience preterm birth. They also had fewer neonatal complications than women who didn’t.

The study followed 458 women with a short cervix who were at greater risk for miscarriage. The women who applied a progesterone gel experienced a 45 percent reduced rate of preterm birth before 33 weeks.

But according to the World Health Organization (WHO) Reproductive Health Library, vaginal progesterone treatment had “no evidence of effectiveness.” The WHO called for further investigations of the links between progesterone and miscarriage prevention.

Warning: Do not use progesterone vaginally if you are pregnant, unless you are using this medication as part of your fertility treatment.

Some women have medical conditions that mean they shouldn’t take Prometrium, vaginally or otherwise.

These include:

Vaginal progesterone has been known to increase a woman’s risk for:

If you have a history of these conditions or concerns about taking vaginal progesterone, talk to your doctor. Prometrium can also interact with some medications.

Side effects associated with vaginal Prometrium can include:

  • breast pain and/or tenderness
  • changes in vaginal discharge
  • drowsiness and fatigue
  • headache
  • mood changes, including increased irritability or nervousness
  • pelvic pain and cramping
  • swelling in the hands or feet

Many of these symptoms are identical to pregnancy complications and can be difficult to recognize.

Using Prometrium vaginally is thought to increase the amount of available progesterone in the uterine lining. This concept is good for women hoping to prevent miscarriage. The goal is to thicken the uterine lining.

When taken orally or injected, progesterone is made available in greater amounts in the bloodstream. But women taking Prometrium vaginally may not have as high levels of progesterone in the bloodstream. This is normal and not a problem because the goal is more progesterone in the uterus, not the bloodstream.

According to InVia Fertility, vaginal progesterone can be as effective as progesterone injections. As a bonus, women don’t have to undergo the sometimes painful injections or risk allergic reaction from the oil used to dissolve the progesterone.

Taking Prometrium or other progesterone doesn’t guarantee that a woman won’t have a miscarriage. But for some women, the medication has been shown to reduce the occurrence of miscarriages. This can help result in a successful pregnancy.

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