There are several ways to calculate luteal phase length. This is the length of time between ovulation and the day prior to menstruation. These methods vary in precision, and those concerned about a short luteal phase, or luteal phase defect may need help from a doctor to get a precise measurement of this interval.
A less “scientific” method is to count back from the date of the period. Since many women have a luteal phase that is about 14 days long, people can determine approximately when ovulation occurred, and how far this occurred after the cycle had begun for a month. This might be enough information to go on for people who have regular periods that are about 28 days in length. It is not always accurate though, since the luteal cycle can range from 10-16 days.
What women need to know to figure out luteal phase length a little more accurately is when they ovulated and when they menstruated afterward. It’s pretty easy to figure out when menstruation occurred, but ovulation tracking might be a little more involved. There are ovulation kits available at stores that could help women determine approximate ovulation time. Alternately people could track possible ovulation with basal body temperature readings, or with analysis of vaginal mucus, which is often taught in natural family planning classes.
With any of these tracking methods, date of ovulation could then be identified. A woman would then count days until she got her period. This time interval would essentially be the luteal phase, and might help determine whether the phase is appropriately long or too short. Anything less than 10 days is considered challenging because the uterus does not build up sufficient lining for a pregnancy to be sustained.
Some women have extremely irregular cycles and they may need greater help in determining exact luteal phase length. This is typically done under doctor’s orders via a blood test. Ovulation time still has to be discovered because the blood test has to take place about seven days thereafter. It evaluates the levels of progesterone in the blood and can much more accurately determine how long a luteal phase length is, and whether this poses a fertility issue that may need to be addressed.
There are fortunately potential treatments for a woman with a short or overly long luteal phase length issues. These can include giving progesterone to stabilize the length. These treatments are not necessarily required unless a woman is trying to get pregnant. Short or long luteal phases may not be medically significant in any woman uninterested in pregnancy