PRETERM LABOR + PROGESTERONE: DAILY SHOTS AND NOT THE FUN COCKTAIL KIND
Where does progesterone come from?Progesterone is actually a type of steroid made from cholesterol. It can be made by the adrenal gland or by the ovaries. Approximately once a month, one of your ovaries releases an ovum—a cell that may or may not become a fertilized egg that develops into an embryo. Before its release, the ovum is supported by a shell of cells called a follicle. After the ovum leaves and starts its journey down a fallopian tube, the empty follicle takes on a new name—the corpus luteum—and a new role of producing lots and lots of progesterone. This rise in progesterone signals the beginning of what’s called the luteal phase of a woman’s cycle, during which time the body’s temperature rises ever so slightly, two other hormones called follicle-stimulating hormone and luteinizing hormone decrease, and estrogen rises.
What’s the role of progesterone in pregnancy?Estrogen and progesterone increase over about six days and signal the tissue in the uterus to thicken and produce more blood vessels so that if the ovum does get fertilized, it can implant into the uterine wall. If the ovum remains unfertilized, levels of progesterone and estrogen taper off over the second week of the luteal phase, the corpus luteum disappears, and all that extra uterine lining and blood flushes out during menstruation. Progesterone will stay low until another ovum leaves an ovary and the whole cycle begins again. If pregnancy does occur, the fertilized egg will make hCG (human chorionic gonadotropin)—the hormone that pregnancy tests detect—which signals the corpus luteum to keep pumping out progesterone for the first trimester of pregnancy. After the first trimester, the placenta can take over the job. Progesterone will continue to rise during pregnancy, during which time it signals changes in breast tissue but prevents lactation until birth. It also causes the pelvic floor muscles to thicken in preparation for delivery and prevents mom’s immune cells from attacking the developing baby.
What happens when progesterone is too low?Low levels of progesterone can cause something called a luteal phase defect, a condition in which a woman doesn’t experience the events of the luteal phase as strongly as most women—for example, her temperature may not rise as much as most women’s do, or the uterine lining may not experience the same changes. A luteal phase defect may also cause the luteal phase to be shorter than average. Either way, many clinicians believe luteal phase defects can make it hard to get pregnant because the uterus never changes enough to support a fertilized egg, or menstruation starts so early that the egg has no chance to implant. Since the uterus needs progesterone to support pregnancy, low progesterone is also believed to be a cause of miscarriage or early labor. There is still controversy about whether luteal phase defects are a cause of infertility all on their own, or whether they only result from other conditions such as thyroid disease, eating disorders, or polycystic ovary syndrome. Part of the problem in diagnosing luteal phase defects is that progesterone naturally fluctuates during a woman’s cycle and even over the course of a day. One study found that the levels of progesterone in a woman’s blood during luteal phase can fluctuate eight-fold within an hour and half. According to WebMD, to diagnose low progesterone or a luteal phase defect, progesterone may have to be tested for several days in a row or even several cycles in a row. Other hormones, such as luteinizing hormone and follicle-stimulating hormone may also need to be measured.
Treating low progesteroneDiagnosing luteal phase defects may be complicated, but there are ways to treat low progesterone. One option is to induce the ovaries to develop and release more ova using hCG or ovulation stimulating drugs like Clomid. The idea is that with each ovum released, the resulting corpus luteum structures will make more progesterone. According to the Practice Committee of the American Society for Reproductive Medicine, however, it’s not clear whether stimulating ovulation treats infertility because it fixes luteal phase defects or if it just improves the odds of pregnancy by causing the body to release more eggs. Another option is to replace progesterone with injections, pills, or vaginal suppositories or creams. Injections seem to provide the highest levels of progesterone. One study found that 100 percent of women who received progesterone treatment for suspected luteal phase defects were pregnant after a year compared to 81 percent of women who took a drug like Clomid. However, the study was retrospective, meaning the researchers surveyed women after the fact. There aren’t good well-controlled studies on the topic because you can’t randomly assign women to treatment or placebo groups when you’re talking about their fertility, not to mention how difficult it is to correctly diagnose luteal phase defects. Because of this, the American Society for Reproductive Medicine doesn’t acknowledge that progesterone increases the rate of natural pregnancies, but it does recommend progesterone for women using assisted reproduction, such as in vitro fertilization. In those cases, progesterone treatment mimics a natural luteal phase and the rates of successful pregnancies. Despite the challenges of researching luteal phase defects and low progesterone, many doctors will still recommend progesterone for women trying to conceive naturally, because in their own experience, it works.
Amanda B. Keener, PhD
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