Luteal phase deficiency (LPD) (or “luteal phase defect”) is a condition that can stop a pregnancy despite an embryo possibly reaching the womb, simply because either (or both):
- The luteal phase is too short
- Progesterone levels are too low
LPD isn’t an absolute, but has degrees to it; so a luteal phase that only lasts nine days is more diagnostic than a phase of eleven days. This also means that LPD can vary from month to month and this variation has divided opinion on it’s relevance to fertility, with experts saying:
- “it may be the most common problem of ovulation that affects women” (i)
- or “LPD, as an independent entity causing infertility, has not been proven” (ii)
There are two other issues in the luteal phase that can prevent pregnancy and they’re:
A healthy luteal phase relies on a healthy corpus luteum developing from the dominant follicle that released the egg, and in LPD the problem is usually due to how well the corpus luteum functions and the amount of progesterone it produces, however it’s interesting that LPD and polycystic ovary syndrome (PCOS) share a number of significant features:
- High anti-Mullerian hormone (AMH) levels
- Defects in the development of the corpus luteum(iii)
The luteal phase starts once an egg is ovulated, and the new corpus luteum transforms itself into a gland that produces progesterone (the ‘hormone of pregnancy’) and this needs to be maintained at a high and stable level for a minimum of 12 days if an embryo is going to implant successfully. In Fig.1 the main changes in the luteal phase (after day 14) are:
- The corpus luteum develops in the ovary
- The basal body temperature (BBT) rises
- The ovaries change the hormones they produce, with a big rise in progesterone
- The womb lining gets ready for implantation
Fig.1: Changes in ovary structure, body temperature and hormones levels in normal menstrual cycles.
In LPD the levels of progesterone are too low and this is crucial for a woman getting pregnant:
- Progesterone needs to be above 10 ng/ml (30 nml/l) for implantation
- Progesterone levels over 17 ng/ml (50 nml/l) are desirable during pregnancy
- Progesterone levels below 7 ng/ml (20 nml/l) cause an inevitable miscarriage
The corpus luteum produces all of the progesterone for the first 8 -12 weeks of pregnancy, until the ‘luteal-placental shift’ is reached at the end of the first trimester. From this point the placenta begins to take over progesterone production and the role of the corpus luteum reduces.
The risk of miscarriage is much higher in the first trimester (there are a number of reasons for this, particularly genetic abnormalities, but also progesterone levels), and after the ‘luteal-placental shift’ the levels of progesterone are able to rise rapidly (they can reach 300-600 nml/l at birth) and the risk of miscarriage reduces. Another cause of low progesterone in pregnancy is thought to be the effect of immune conditions on hormone production.
Because progesterone affects the basal body temperature, it means that when there’s low progesterone the temperatures in the luteal phase are lower, and unstable progesterone levels create unstable BBT patterns in the luteal phase. This makes temperature charting an excellent way to diagnose LPD (over a number of months) to back up the standard blood test 7 days after ovulation (which is usually only done once). This is one part of a much fuller explanation of the diagnosis and treatment options of LPD available to you.
(i) ‘The diagnosis of luteal phase deficiency: a critical review.’ McNeely MJ, Soules MR. Fertil Steril. 1988 Jul;50(1):1-15.
(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.