LMP has various meanings in medicine, and there are two commonly used meanings, including last menstrual period and left chin posterior position (fetal position) in obstetrics and gynecology. The last menstrual period is usually used to calculate the due date of a pregnant woman, while the left chin posterior position (fetal position) is a reference basis for choosing the mode of delivery of a pregnant woman.1. Last menstrual period: In English, the last menstrual period is called last menstrual period, so the last menstrual period is abbreviated as LMP. The LMP also indicates that the fetus is in a left mentoposterior position when the baby is about to be delivered, with L indicating the left side of the pelvis and M indicating the left side of the pelvis. L is the left side of the pelvis, M is the bottom of the pelvis, and P is the posterior position of the pelvis, which is a relatively rare fetal position. This type of fetal position may cause obstructed labor and pose a risk to the life of the mother and the fetus, so a left chin posterior position before delivery usually requires a cesarean section.