For pregnancy, does the “last menstrual period” refer to the start or the end date?
Aug 24, 2022
Source: Cainiu Health
Dr. Lv Aiming
Introduction
Pregnancy is dated from the first day of the last menstrual period (LMP). According to standard medical practice for estimating the due date, healthcare providers typically calculate gestational age from the LMP, with the full term of pregnancy being 40 weeks—or approximately 10 months. If a woman has a regular 28-day menstrual cycle, the expected date of delivery (EDD) is calculated using the Gregorian calendar: add 9 months to the month of the LMP (or subtract 3 months), and add 7 days to the day of the LMP.
Women of normal childbearing age may become pregnant if they engage in sexual intercourse. Generally, the first sign of pregnancy is a delayed menstrual period. Additionally, fatigue, drowsiness, and bloating are common and normal symptoms during early pregnancy. So, when referring to the “last menstrual period” (LMP) in pregnancy, does it denote the start or the end date of the period?
Does the “last menstrual period” refer to the start or the end date?
The “last menstrual period” refers to the first day of the most recent menstrual cycle. In clinical practice, gestational age and the estimated due date (EDD) are calculated from this date. According to standard obstetric convention, a full-term pregnancy lasts 40 weeks (approximately 10 months), counted from the first day of the LMP. For women with a regular 28-day menstrual cycle, the EDD is calculated using the Gregorian calendar: add 9 months (or subtract 3 months) to the month of the LMP, and add 7 days to the day of the LMP. If a woman has irregular cycles or an unstable menstrual pattern, early pregnancy ultrasound is recommended to assess gestational age—specifically by measuring the size of the gestational sac—and to corroborate findings with the timing of early pregnancy symptoms (e.g., nausea, breast tenderness) or the onset of fetal movement.
Each pregnant woman has unique physiological characteristics and fetal development patterns; therefore, the exact timing of delivery varies. However, deliveries occurring at or after 37 completed weeks of gestation are considered full-term. During pregnancy, women should maintain a balanced, nutritious diet and avoid colds, heavy lifting, and exposure to harmful substances. Should vaginal bleeding, abdominal pain, or any other unusual symptoms occur, prompt medical attention is essential.
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