The luteal phase of the menstrual cycle spans the time between ovulation and the onset of the next menses. Luteal phase defect (LPD) is a common but misunderstood condition that frequently affects fertility.

Many people describe LPD in terms of its symptoms, e.g., a shortened luteal phase or disrupted basal body temperatures (BBTs). Quite simply, however, LPD is a failure of the uterine lining to be in the right phase at the right time. Since embryo implantation is highly dependent on the state of the lining, LPD can consistently interfere with a woman's ability to get pregnant and carry a pregnancy successfully.

A Normal Menstrual Cycle

In an ideal menstrual cycle, the body begins to produce follicle stimulating hormone (FSH) several days after the onset of menses. The increased levels of FSH result in the formation of a mature egg-containing follicle on one of the ovaries. When the follicle has adequately matured, a surge of luteinizing hormone (LH) is triggered. This surge performs two interrelated functions:

  • It prompts the follicle to burst and release the egg into the fallopian tube, where fertilization may take place.

  • As the follicle begins to refill after bursting, the increased levels of LH cause the fluid inside the follicles to change into a thicker yellowish substance.

The resulting structure is now called a corpus luteum rather than a follicle, and it is responsible for producing the hormone progesterone in the second half of the cycle. As a result of elevated progesterone levels, the uterine lining will thicken and develop additional blood vessels, which gives the embryo a place to attach. Progesterone will also prevent a premature onset of menses in which a pregnancy might be lost. In a normal menstrual cycle, the corpus luteum will produce progesterone for approximately twelve days.

A Cycle with LPD

A normal cycle can be disrupted in several places. Three causes of LPD include poor follicle production, premature demise of the corpus luteum, and failure of the uterine lining to respond to normal levels of progesterone. These problems can also be found in conjunction with each other.

Poor follicle production has its origins in the first half of the cycle. The body may not produce a normal level of FSH, or the ovaries do not respond strongly to the FSH, leading to inadequate follicle development. Because the follicle ultimately becomes the corpus luteum, poor follicle formation leads to poor corpus luteum quality. In turn, a poor corpus luteum will produce inadequate progesterone, causing the uterine lining to be adequately prepared for the implantation of a fertilized embryo. Ultimately progesterone levels may drop early and menses will arrive sooner than expected.

Premature failure of the corpus luteum can occur even when the initial quality of the follicle/corpus luteum is adequate. For reasons not wholly understood, the corpus luteum sometimes does not persist as long as it should. Initial progesterone levels at five to seven days past ovulation may be low; even if they are adequate, the levels drop precipitously soon thereafter, again leading to early onset of menses.

Failure of the uterine lining to respond can occur even in the presence of adequate follicle development and a corpus luteum that persists for the appropriate length of time. In this condition, the uterine lining does not respond to normal levels of progesterone. Therefore, should an embryo arrive and try to implant, the lining will not be adequately prepared, and the implantation will likely fail.

Diagnosis and Treatment of Luteal Phase Deficiency

With the above information, it is easier to understand the many symptoms associated with LPD. Progesterone is responsible for the rise in basal body temperature during the luteal phase. Women who monitor their basal body temperature will thus often note that luteal phase temperatures do not stay reliably elevated for twelve days. Additionally, women who monitor the time of ovulation often notice that their next cycle begins sooner than the normal 12-14 days after ovulation.

Once a diagnosis of LPD is suspected, a serum progesterone test will often be performed at about seven days past ovulation. A level less than 14 ng/ml indicates that progesterone production in the luteal phase is inadequate.

Should progesterone levels prove to be low, the temptation is often to "treat the symptom" by giving the patient progesterone supplementation during the luteal phase. In the case of inadequate corpus luteum performance, progesterone support may indeed be the appropriate solution. However, inadequate follicle development may also be causing the low progesterone levels. Thus, it is important to measure midcycle follicle size (via ultrasound) and estradiol levels (via a blood test).

If follicle development is normal, then progesterone supplementation during the luteal phase is normally the correct treatment. If follicle development is inadequate, an ovulatory stimulant such as Clomid or an injectable drug may be in order; these drugs help the follicle to mature more appropriately, which has the double benefit of producing a higher quality egg and a better-functioning corpus luteum.

Women whose linings fail to respond to normal progesterone levels often have normal follicle development and adequate progesterone levels at 7 days past ovulation. An ultrasound image of the lining at seven dpo, however, will show a lining that has failed to convert from the triple layer lining typical of the time of ovulation. In this case, women are often given additional progesterone supplementation in the luteal phase in the hope that a higher level will be the push that the lining needs to convert appropriately. Some doctors use injections of human chorionic gonadotropin to further stimulate the corpus luteum. However, these injections can cause false positive pregnancy results.

Endometrial Biopsies

An endometrial biopsy is the gold standard in diagnosing LPD. Many doctors feel comfortable basing an LPD diagnosis on progesterone levels, luteal phase length, and ultrasound lining appearances. However, especially in persistent cases, many doctors will use an endometrial biopsy.

The endometrial biopsy is normally performed a few days before the next menstrual cycle is expected, ideally after a negative pregnancy result for the cycle has been obtained. The procedure consists of sampling a small amount of uterine lining and sending it to a pathologist for evaluation. Because the evaluation is done at a cellular level, the knowledge gained from it is at its most detailed and precise. The pathologist categorizes the lining as being typical of a particular cycle day. If this categorization is consistent with the actual cycle day that the sample was taken, the result is considered normal, and the uterine lining is in phase. If there is a discrepancy of more than two days, the lining will usually be considered out of phase.

LPD is a common disorder, but it is fairly easy to diagnose and, in most cases, it is extremely responsive to the correct treatment. The most important part of the process is determining the exact cause, because that will determine the most appropriate treatment.

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