The hormone progesterone plays an integral role in maintaining the uterine lining so an embryo can implant and grow. The corpus luteum, the leftover remnant of the follicle that produced an egg that month, produces progesterone starting immediately after ovulation. If an embryo implants, it signals the corpus luteum to keep producing progesterone. The placenta gradually takes over progesterone production around 10 weeks into pregnancy as the corpus luteum disintegrates. Low progesterone levels early in pregnancy can have a number of causes; treatment of low progesterone depends on the cause.
Progesterone levels rise throughout pregnancy but normally range between 12 and 20 nanograms per milliliter through the first five to six weeks of pregnancy, the American Pregnancy Association states. A progesterone level of 5 ng/ml or less in early pregnancy rules out a normal intrauterine pregnancy in 99.8 percent of cases, Dr. Beata E. Seeber of the University of Pennsylvania says in the February 2006 issue of "Obstetrics and Gynecology." A progesterone level below 14 ng/ml is inadequate, according to INCIID. The mean progesterone level at four weeks of pregnancy, around the time of the first missed period is 21.6 ng/mL, the Center for Reproductive Immunology and Genetics reports.
Before determining how to treat low progesterone levels, it's important to establish the cause. An abnormal intrauterine pregnancy and an ectopic pregnancy, which implants outside the uterus, can cause low progesterone levels. Giving progesterone in these cases would serve no point, since the pregnancies will not survive. In some women, the corpus luteum is not producing a sufficient amount of progesterone. Women with luteal phase defect, who get their periods normally only 10 or so days after ovulation rather than 12 to 14 days, have a corpus luteum that fails prematurely. When the corpus luteum fails, progesterone levels drop and the uterine lining breaks down. Giving supplemental progesterone in these cases can help prevent early miscarriage. Pregnancy will fail if progesterone levels fall too low, according to the Center for Reproductive Immunology and Genetics.
Progesterone supplements come in several forms: injections, vaginal suppositories and creams, and micronized oral pills. It's important to take prescription progesterone and not over-the-counter forms, which may contain little actual progesterone. Vaginal progesterone is best absorbed, followed by injection and oral forms, the Center for Reproductive Immunology and Genetics says. Synthetic progesterone, found in some types of hormone replacement therapy and birth control pills should not be taken in pregnancy.
By 10 weeks, the placenta normally takes over progesterone production. If the placenta and pregnancy are normal, progesterone levels may rise to normal levels and supplemental progesterone can possibly be stopped. Do not stop progesterone without your medical provider's approval.