Your menstrual cycle is made up of three parts: before ovulation (follicular phase), ovulation, and after ovulation (luteal phase). Each part of the cycle has different hormone levels and physiological symptoms triggered by these different hormone levels.

During the first part of your cycle, the follicular phase, your estrogen levels begin to rise. AT the same time, your progesterone is very low (has just dropped), and this sudden drop in progesterone followed by a rise in estrogen, stimulates your uterus to first shed (your period) and then regrow a thick, blood-filled lining (called the endometrium) that is necessary to sustain a pregnancy. The rising estrogen is made by the follicles that are developing in your ovaries, 15-20 eggs per ovary are developing every month of your cycle, and only the biggest and best 1-2 will be "good enough" to be ovulated (this is why this part of the cycle is called "the follicular phase", because it's the part of your cycle where the follicles are in control.)

While all this is happening, your rising estrogen also encourages tiny canyons in your cervix called "cervical crypts" to begin making a lot of "egg white cervical mucus", an alkaline fluid that goes out into the vagina and will help keep sperm alive. It also causes cells to grow in your Fallopian tubes that make alkaline fluids that help sperm to stay alive to reach an egg. When your estrogen levels get high enough (as the eggs mature, they make more and more estrogen), your body releases a burst of a hormone called "luteinizing hormone" that causes the skin around your biggest and best egg to grow thin and the egg pops out.

Your follicular phase can last for any length of time, it all depends on how long it takes for your eggs to make enough estrogen to trigger the LH surge (the LH surge is what you are testing for when you use OPK)

Once you ovulate, you enter your luteal phase. Your estrogen drops and the empty spot the egg came out of, turns into the "corpus luteum" and this starts making progesterone. This progesterone helps make the uterine lining that the estrogen grew, to be nice and welcoming for a fertilized egg. The corpus luteum has a limited lifespan though - it only lasts about 14 days, unless you are pregnant, in which case the little bean sends signals to your body to keep producing progesterone and sustain the pregnancy. If you aren't pregnant, your progesterone drops and your uterine lining comes off, in a process that we all know too well as menstruation or AF ("Aunt Flo") The first day of bright red bleeding is the beginning of a new menstrual cycle, or CD 1 (Cycle Day 1).

Sometimes, things don't go quite right with this process and your luteal phase doesn't last for a full 14 days. Anywhere from 12-14 days is considered normal. This gives plenty of time for the egg to be fertilized, to move down the Fallopian tubes into the uterus, and implant there well enough to send the message to your body to continue producing progesterone and maintain the uterine lining. You can get pregnant with a LP of 10-12 days, but anything shorter than that means that something is not functioning quite right and your body may just not "want" to be pregnant that month (some researchers believe that a short LP is a kind of natural birth control that your body uses to prevent pregnancy when circumstances are less than ideal). If this is the case, please don't despair, most of the time your body will straighten it all out over the course of a few cycles.

Oftentimes doctors will give supplementary progesterone to women with a short LP or during a pregnancy that seems to be low in progesterone. Unfortunately, the scientific data indicates this does nothing to sustain a pregnancy, especially in women with a normal or near-normal LP who just have lower progesterone for some reason during pregnancy. If your progesterone is lower than normal during pregnancy, it is likely because the pregnancy is not viable and the embryo is not sending the right kind of signals to your body to sustain the pregnancy - all the progesterone does is delay the inevitable. If your luteal phase is short, it is best to treat the problem rather than use prog supps because they simply don't work - if your pregnancy works out, it's because your baby sent signals to your body to increase production of progesterone and not because of the progesterone supps.

PLEASE do not use the OTC progesterone creams - they are designed for postmenopausal women and do not have the right amount of progesterone to sustain a pregnancy, even if progesterone supplementation DID work (which data indicates it does not.) And PLEASE PLEASE PLEASE do not use these OTC progesterone creams in your follicular phase before ovulation, regardless of what you read on other sites. You are SUPPOSED to be lower in progesterone during your follicular phase.

To treat a shorter than normal LP naturally without affecting a sway, increase intake of fats (pink swayers will want to increase fat intake only slightly, blue swayers, you have more leeway), get a long uninterrupted block of sleep at night without artificial lighting, reduce breastfeeding, and take a big dose of Vitamin P - patience. Most short LPs will work themselves out over the course of a few months without your doing or taking anything at all. The best medical treatment for short LP is Clomid.