Progesterone Injections to Maintain Pregnancy

When you're pregnant, the hormone progesterone plays an essential role in helping your baby grow. Most women have adequate progesterone levels without taking progesterone supplements. But if you have a history of unexplained pregnancy loss or if you've undergone fertility treatments, your doctor might prescribe progesterone injections to boost your progesterone levels. Giving progesterone properly helps prevent complications such as infection at the injection site and may decrease the risk of pregnancy loss.

Progesterone Production During Pregnancy

For the first weeks of pregnancy, progesterone is produced in the ovary by the corpus luteum, which is the leftover "shell" of the follicle that once contained the egg that was fertilized to become your baby. By around week 8 of pregnancy, the placenta takes over production of progesterone and the corpus luteum disappears. Progesterone is absolutely necessary in early pregnancy. If you don't produce adequate levels of progesterone on your own, your uterine lining, where the baby grows, might not be able to sustain your pregnancy.

Reasons for Progesterone Injections

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If you've undergone fertility treatments, your doctor will likely prescribe some form of progesterone supplement to keep your estrogen and progesterone levels in balance. Undergoing frozen embryo transfer can also necessitate progesterone treatment because you generally won't ovulate around the transfer time, so a corpus luteum will not be formed. A history of repeated miscarriage without a known cause, a history of preterm labor or a cervix that's shorter than normal are other reasons why your doctor might prescribe progesterone injections. Progesterone supplementation won't prevent all miscarriages or preterm labor, however. According to an article published in the summer 2011 issue of "Reviews in Obstetrics and Gynecology," it can reduce the risk of recurrent preterm labor in about 33 percent of cases.

How to Administer Progesterone

Progesterone can be given vaginally or as an injection. Progesterone injections must be given in a muscle, while vaginal progesterone comes in capsule or gel form. Studies have not proved injections to be more effective than vaginal suppositories, according to a July 2009 article in "Fertility and Sterility." The upper outer quadrant of the buttocks is the preferred site for injection if someone else is giving you the injection. If you have to administer the injection yourself, it is generally easier to inject into the upper thigh muscle. Follow your doctor's instructions regarding drawing up and injecting the medication and how often to inject it.

Common Side Effects

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Any injection may cause side effects or complications. Infection can occur at the injection site, causing redness, swelling or pain in the area. Progesterone can also cause a localized reaction, with hard lumps, redness or itching around the injection site. Possible side effects of any form of progesterone include drowsiness, fluid retention, increased breast tenderness, nausea, increased irritability, diarrhea or depression. The good news is that the overwhelming majority of scientific studies have found that progesterone injections during pregnancy cause no harm to the developing baby, according to an article published in the April 2008 issue of “Fertility and Sterility.”

Potentially Serious Reactions

Blood clots can develop while taking progesterone. Call your doctor right away if you think you have symptoms of a blood clot. These include leg swelling, redness in your leg, a warm spot on your leg or leg pain that worsens when bending your foot. Although an allergy to progesterone itself will not occur, it is possible to have an allergic reaction to substances added by the manufacturer when making the progesterone solution, such as cottonseed or sesame or peanut oil. Seek professional help immediately if you experience a rash, hives, itching, significant redness at the injection site, swelling or difficulty breathing.