What is a luteal phase defect ?

Luteal phase defect ( LPD) used to be a very popular diagnosis many years ago. While most doctors today do not believe that this entity even exists, unfortunately, it’s still “diagnosed” commonly – and causes a lot of overtesting and overtreatment ! Let’s see why.

The luteal phase is the second half of the menstrual cycle during which the corpus luteum produces progesterone to maintain the endometrial lining of the uterus so that an embryo can implant in it . At the time of ovulation, the mature follicle releases the egg . It then gets converted into a yellow body called the corpus luteum, under the influence of the luteinizing hormone ( LH) produced by the pituitary. ( Remember that it's this LH surge which is responsible for the ovulation !) If the embryo implants successfully, the corpus luteum continues to be supported by the HCG produced by the embryo because the biological activity of HCG and LH is very similar. It now becomes a corpus luteum of pregnancy, which continues producing progesterone , the hormone which supports the pregnancy.

However, if no embryo implants, then the corpus luteum starts to disintegrate because the LH levels start to decline. The corpus luteum has a life span of about 14 days, and when it starts to die, the progesterone levels start to decline as well. Because the uterine lining now no longer gets the progesterone support it needs, it starts to shed, and the period begins.

In most fertile women, the luteal phase is usually 14 days. This means that the time between ovulation and the next period is fairly constant for most women.

Progesterone is the hormone ( a chemical messenger) produced by the ovaries that is necessary to support pregnancy. Progesterone is produced by the corpus luteum of the ovary after ovulation; and is essential for ripening the uterine lining so that the embryo can implant in it. Progesterone rises in the blood following ovulation, peaks on Day 20, and then declines .

The level of progesterone can be measured by doing a simple blood test. Normally, the progesterone level should be more than 15 ng/ml about 7 days after ovulation. This suggests that the corpus luteum is functioning normally. A very low Day 21 progesterone levels suggests the cycles was anovulatory ( no egg was produced).

In some women, even though ovulation does occur normally, the corpus luteum is of poor quality, as a result of which it does not produce enough progesterone. Doctors used to believe that low progesterone levels during the luteal phase could cause “ unexplained infertility “ and miscarriages. This was quite an attractive hypothesis and was popular for many years. After all, embryo implantation depends upon a ripe secretory uterine lining, which in turn depend upon adequate progesterone production by the corpus luteum. It was very easy to conclude that a poor quality corpus luteum could cause infertility – and since BBT charting used to be so popular , doctors would carefully scrutinise the BBT charts, to look for the duration of the luteal phase; and the duration and extent of the rise in the BBT after ovulation. If the luteal phase was shortened; or if the rise in the BBT after ovulation was sub-optimal, they would make a diagnosis of LPD.

In order to confirm this, additional tests were ordered. These included a blood test to check the progesterone level; and a painful endometrial biopsy, to take out a strip of the uterine lining and send it for histological examination.

An endometrial biopsy was the gold standard in diagnosing LPD. The endometrial biopsy is normally performed a few days before the next menstrual cycle is expected . 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 and a diagnosis of LPD made.

The reason this diagnosis has now fallen out of favour is that we have realized that many normal fertile women also have LPD ! This is why few doctors bother to make this diagnosis, because it not affect the clinical outcome at all.