Luteal phase deficiency (LPD) is also called “luteal phase defect” and it can prevent pregnancy even when an embryo implants in the womb. As the name implies, LPD is a dysfunction of the menstrual cycle’s second (luteal) phase, and there are two possible causes, which are often seen together:
- The luteal phase is too short
- Progesterone levels are too low
There are degrees of LPD rather than it being absolute, so a luteal phase of nine days is more diagnostic than an eleven-day phase. It’s also possible for LPD to vary from month to month, which has divided expert opinion on how relevant it is to fertility, which ranges from:
“it may be the most common problem of ovulation that affects women” (i)
to
“LPD, as an independent entity causing infertility, has not been proven” (ii)
It’s worth noting that LPD and polycystic ovary syndrome (PCOS) share significant features:
- Hyperinsulinaemia
- High anti-Mullerian hormone (AMH) levels
- Defects in the development of the corpus luteum iii
The luteal phase
A corpus luteum develops from the empty dominant follicle and produces progesterone after ovulation. Progesterone is known as the “hormone of pregnancy” and it needs to be at a high and stable level for at least 12 days for an embryo to implant (Fig.1 shows how the luteal phase develops after day 14):
- The corpus luteum develops
- The basal body temperature (BBT) rises
- Hormone production shifts with a significant rise in progesterone
- The womb lining gets ready for implantation
Fig.1: Changes in ovary structure, body temperature and hormone levels in regular menstrual cycles
In LPD, the progesterone levels are too low, which is crucial for getting pregnant:
- Progesterone needs to be above 10 ng/ml (30 nml/l) for implantation
- Pregnancy requires progesterone levels over 17 ng/ml (50 nml/l)
- If progesterone falls below 7 ng/ml (20 nml/l), a miscarriage is inevitable
LPD and temperature
Because progesterone raises the basal body temperature (BBT), temperatures in the luteal phase can indicate LPD (and hypothyroidism):
- Low temperatures in the luteal phase indicate low progesterone
- Unstable progesterone levels create irregular BBT patterns
Several temperature profiles can help indicate what’s causing the unstable luteal phase. Charting over several months is a valuable way to expand on the results of blood tests after ovulation (which is usually done once only). Two other issues that can prevent pregnancy in the luteal phase are:
(ii) ‘The clinical relevance of luteal phase deficiency: a committee opinion.’ Fertil Steril. 2012 Nov;98(5):1112-7.
(iii) ‘Common pathophysiological mechanisms involved in luteal phase deficiency and polycystic ovary syndrome. Impact on fertility’ Georgios Boutzios, Maria Karalaki, Evangelia Zapanti Endocrine April 2013, Volume 43, Issue 2, pp 314-317.
