The luteal phase is the second half of your menstrual cycle. It’s the part of the cycle that comes after ovulation, when the egg already has—or hasn’t—been fertilized, and you’ve nothing left to do but wait.
But even though it comes after conception, the luteal phase plays a critical role in your ability to get pregnant.
Most importantly, the luteal phase must be long enough to allow for the fertilized egg to properly implant in the uterus and start signaling to your body that you’re pregnant. Otherwise, your period will start, and the egg will be washed out with the menstrual blood.
How long does the luteal phase need to be?
The first part of your cycle, the follicular phase, starts on the first day of your period and ends with ovulation.
The second half, the luteal phase, runs from the first day after ovulation until the last day before your next period. Neither the day of ovulation, nor the first day of your period, should be included when you count the number of days in your luteal phase.
For most women, the luteal phase lasts between 12 and 16 days, with an average of 14 days. Any number of days between 10 and 18 is considered normal, but if your luteal phase is shorter than 12 days, it might be more difficult to get pregnant.
As this indicates, there is great variation between women when it comes to the luteal phase length. In an individual woman, however, the length of the luteal phase is usually stable.
The length of your follicular phase (before ovulation) can vary considerably from one cycle to another, but the luteal phase will typically be the same length in every cycle.
The corpus luteum and the hormone progesterone
Before ovulation, a handful of eggs are slowly maturing, each nested in its own follicle (a fluid-filled sac in the ovary). During ovulation, one of the follicles ruptures and releases the egg, so that it can be fertilized.
But the now-empty follicle continues to play a key role in the process. Immediately following ovulation, it transforms into a structure called the corpus luteum, Latin for “yellow body”, which gives the luteal phase its name.
The corpus luteum now secretes the hormone progesterone (and to a lesser extent, a few other hormones as well). Progesterone is responsible for building up and thickening the lining on the inside of your uterus, so that if the egg was fertilized, it can attach itself to this soft, nutritious uterine lining in the process known as implantation.
For as long as the corpus luteum is producing progesterone, the uterine lining is sustained. If the egg wasn’t fertilized, the production will gradually diminish, and the corpus luteum decays. The uterine lining is shed as menstruation, and the body starts the whole process over again in a new cycle.
If a fertilized egg has implanted in the uterine wall, on the other hand, it will start to produce the hormone hCG (the hormone that’s detected by pregnancy tests). hCG stimulates the corpus luteum to continue producing progesterone, thereby preventing the onset of menstruation.
In a successful pregnancy, the corpus luteum produces progesterone for 8-12 weeks, after which the placenta takes over this function.
Besides sustaining the uterine lining, progesterone also causes the basal body temperature to rise just a little. By measuring and recording your temperature daily, this shift can be observed, which makes it possible for you to pinpoint the ovulation day.
Luteal phase defect: How to fix a short luteal phase
Luteal phase defect is a condition where the luteal phase is shorter than normal, the level of progesterone during the luteal phase is lower than normal, or both.
When the corpus luteum stops producing progesterone too early, menstruation will start before the fertilized egg has had time to implant properly. The result is a very early miscarriage, also known as a “chemical pregnancy”.
If you suspect that your luteal phase is too short, you should measure your basal body temperature for 2-3 cycles in order to calculate the exact length of your luteal phase. Remember that neither the day or ovulation nor the first day of your period should be included.
If your luteal phase is shorter than 12 days, see your doctor or gynecologist to discuss progesterone supplementation and other treatment options.
Some women experience improved luteal phase length when they take large doses of vitamin B6 (100-150 mg per day). If you would like to try this, you must buy your vitamins in the form of pyridoxine at the pharmacy or online. Regular vitamin B6 supplements don’t contain sufficient doses.
As always, consult your physician before starting any fertility-related self-treatment.