The lining of the uterus, the endometrium, must thicken and become more vascular during the ovulatory cycle. Otherwise, it will not be able to provide sufficient support and nourishment to a developing embryo. The "thickening" occurs under the influence of two hormones, progesterone and estrogen. An underdeveloped endometrium can also lead to early miscarriage.
A small sample of the endometrium can be taken during the luteal phase of the menstrual cycle approximately twelve days after the LH surge and ovulation and 1-2 days before menstruation. The biopsy can be examined to see if the cellular structure and development of the endometrium “matches” the cycle day or is “in phase”. If a sample taken at this time shows little development, a luteal phase defect may be present.
This test was commonly performed in the past but is used infrequently currently due to the discomfort, high cost and marginal value. In addition, the results determining whether the endometrium is “in phase” are often inaccurate. Currently blood tests for progesterone, in conjunction with determining the length of the luteal phase, are used to help evaluate this potential problem.
Medications to enhance ovulation, or progesterone, may be administered in the next treatment cycle to correct the luteal phase defect if it is suspected. Typically ovulation enhancement is often the next line of therapy for many patients. This is a good treatment for many patients who in the past may have been diagnosed with a luteal phase defect by biopsy.
The endometrial biopsy may be considered in certain circumstances such as for performing the E-tegrity test to evaluate the endometrium for the presence of certain substances (beta 3 integrins) that are felt to be necessary for implantation. It can also be used to evaluate the patient for chronic endometritis (endometrial infection) or endometrial hyperplasia (thought to be a precursor to endometrial cancer). Endometrial hyperplasia is more common in women with PCOS who have not used fertility drugs to induce regular cycles.