For two hundred years, generations of women have been given EDDs based on this simple and relatively reliable rule.ĮDDs calculated using Naegele's Rule differ slightly from each other depending on the particular months being counted but always result in a length of pregnancy that is close to or exactly 280 days. It made sense to measure pregnancy from the start of menstruation, a date easily observable to women. When Naegele's Rule was first created, the medical community didn't know when conception occurred so Naegele, in turn, credited a Dutch professor of botany and medicine (Herman Boerhaave) from the 1700's for its creation. Popularized the simple formula in the early 1800's. Naegele's Rule is named after the German professor of obstetrics who The modern formula, LMP + 280 days = EDD, is based on a Naegele's Rule and the History of the Due Date Calculator When counted from LMP, pregnancy is 280 days, or 40 weeks, from the first day of a woman's last menstrual period to estimatedĪctual length of pregnancy: The actual length of pregnancy varies considerably,Įstimated due date should be thought of as an indication of a range, or timeįrame, when baby might come. The terminology of pregnancy dating is based on the LMP formula.Ĭounting pregnancy from LMP is the basis of gestational ageing which is the way pregnancy progress is It is also the appropriate methodįor calculating due dates when pregnancies result from artificial reproductive Not yet been performed or is not available. When to use the LMP formula: Despite its inherent weaknesses, the LMP formula is great for pregnancy dating when ultrasound has This canīe a little confusing since counting starts about two weeks before true pregnancy begins.īut it does provide a useful starting point for calculation of due dates and Normally known, the LMP formula begins counting pregnancy from the first day of a women's last menstrual period (LMP). Since the actual date of conception is not Obstetricians has issued recommendations which define when it isĪppropriate to use an LMP formula to calculate an EDD and when an ultrasound In the US, the American College of Gynecologists and The first trimester is the most accurate method for establishing or confirming aĭue date.
Assumptions Made By Due Date Calculatorsĭue dates can be calculated either by formula or from ultrasound measurements ofįormulas are quick and easy and can be used by anyone.