What is luteal phase and why is it important?
The time from ovulation till the periods is called luteal phase.
Following ovulation, corpus luteum is formed, which secretes mainly progesterone and also some oestrogen.
Progesterone prepares the uterus for embryo implantation.
In absence of pregnancy, the corpus luteum degenerates 9-11 days after ovulation resulting in fall in the level of progesterone.
This in turn leads to shedding of the uterine lining and vaginal bleeding during periods.
In the event of pregnancy, the pregnancy hormone, HCG (human chorionic gonadotrophic hormone), maintains the corpus luteum and stops it from degenerating.
The function of corpus luteum is essential for first 7-9 weeks of pregnancy, after which the placenta takes over.
Progesterone is important for embryo implantation and maintenance of early pregnancy. Inadequate luteal phase or progesterone can lead to infertility/miscarriage.
What is short luteal phase?
Normal luteal phase duration is mostly 14 days.
However, it can vary between individuals and luteal phases lasting between 11-17 days are considered normal.
A luteal phase ≤8-10 day is considered short.
Many women can have occasional one or two cycles with short luteal phase. This does not impact their chances of natural conception.
A short phase (<8 days) can only cause a delay in conception if it is consistently present in most months. Studies have shown that the chances of such persistent short luteal phase are quite small (<3%).
What is luteal phase defect?
Luteal phase is considered defective or deficient if the progesterone level is not sufficient to maintain the uterine lining (endometrium) for embryo implantation or growth.
However, it is highly controversial if luteal phase defect at all exists.
The controversy arises due to the following facts:
Cycle length can vary month to month in the same woman, who is perfectly ovulating, depending on number of days required for ovulation.
The progesterone is secreted by the corpus luteum in a pulsatile fashion. The progesterone level can be low in between the pulses. So it is possible to find a relatively low progesterone level in a totally normal luteal phase.
There is a lack of reliable test to diagnose this disorder.
The progesterone level in early pregnancy is a combined contribution from corpus luteum and also from the developing embryo. Hence a low progesterone in early pregnancy can mean a defective corpus luteum or intrinsically abnormal pregnancy that is destined to miscarry or both.
What causes luteal phase defect or short luteal phase?
It is a subtle form of ovulation defect. Altered hormone levels causing defective ovulation can cause luteal phase defect.
Excessive exercise, anorexia, eating disorder, severe stress can cause hormonal imbalance by suppressing hypothalamus (gland in the brain). This can cause luteal phase defect.
Thyroid and prolactin disorders can also cause hormonal imbalance and cause problems with ovulation and in turn luteal phase defect.
Obesity, smoking is also found to be associated with luteal phase defect.
Older women, with hormone dysfunction are also at higher risk of having luteal phase defect.
Can low ovarian reserve cause short luteal phase?
Low ovarian reserve in younger women is not associated with luteal phase defect, a study involving 755 women showed.
Luteal phase defect symptoms:
There are no specific symptoms of luteal phase defect.
It can be associated with:
Pre-menstrual spotting,
Having period within a week of positive ovulation test
Luteal phase defect diagnosis:
Diagnosis of luteal phase defect is difficult due to the challenges discussed above.
According to ASRM, there is no proven practical standard to diagnose luteal phase defect.
The only way to diagnose a short luteal phase is to check the number of days from positive surge on urinary ovulation test and time of onset of periods.
An interval of 8 or fewer days from time of positive ovulation test to menstruation is considered short as per ASRM.
Checking progesterone level is NOT a diagnostic tool to detect luteal phase defect. Progesterone level can vary from cycle to cycle and also in the same cycle as it is secreted in pulses. There is no minimal fertile level for progesterone. Hence it should not be used to diagnose luteal phase defect.
Endometrial biopsy is not a reliable tool to differentiate fertile women and women with luteal phase defect according to randomised controlled trials.
Basal body temperature is also not a reliable method to diagnose luteal phase defect and hence not recommended.
What are the treatment options?
Treatment is indicated only for women with persistent short luteal phase <8 days, as detected from urinary ovulation test and onset of menstrual bleeding.
Treatment would include correction of life style factors, such as avoiding smoking, reducing weight for obese but avoiding excessive exercise.
Correction of thyroid or prolactin defects if any.
Correction of defect in ovulation using ovulation-inducing agents like clomiphene citrate/letrozole. However, these treatments should be undertaken with strict ultrasound monitoring due to risk of multiple pregnancies.
Using progesterone supplement after ovulation to correct the luteal phase should be avoided, as it delays menses and creates false expectation of pregnancy, increases stress.