Last Menstrual Period (LMP)

Definition - What does Last Menstrual Period (LMP) mean?

Last menstrual period (LMP) refers to the start date of a woman’s most recent menstrual period as indicated by the first day of bright red bleeding. A typical menstrual cycle is around 21-35 days in length, with the first day of menstrual bleeding signifying day 1 of the cycle.

Because most women have a relatively predictable pattern when menstruation occurs, the start date and duration of the last menstrual cycle can provide important insight, including when the next menstrual period will occur, the time frame in which a woman is fertile and ovulating, or if pregnant, the approximate due date and gestational age of the fetus.

FertilitySmarts explains Last Menstrual Period (LMP)

The first day of bleeding in a woman’s period is notable as it is the date can be used to estimate the timing of ovulation (around day 14 for women with a normal cycle) and to calculate the length of her cycle. Understanding this cycle and awareness of its stages, known as fertility awareness, is an effective way to increase the odds of conceiving through intercourse.

The more accurately a cycle is tracked and charted, the more precisely ovulation days can be identified. Additionally, if infertility problems are present, this awareness will assist a physician in diagnosing any issues.

LMP is also used to calculate an estimated due date where spontaneous labor may occur during pregnancy. This date is estimated by adding 280 days to the first day of the last menstrual period.

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