History
Naegele's Rule is named after Franz Karl Naegele (1778–1851), the German obstetrician who devised the rule. Naegele was born July 12, 1778, in Düsseldorf, Germany. In 1806 Naegele became ordinary professor and director of the lying-in hospital in Heidelberg. His "Lehrbuch der Geburtshilfe," published in 1830 for midwives, enjoyed a successful 14 editions.
The rule estimates the expected date of delivery (EDD) (also called EDC, for estimated date of confinement) from the first day of the woman's LMP by adding 1 year, subtracting three months and adding seven days to that date. The result is approximately 280 days (40 weeks) from the LMP.
Example:
LMP = 8 May 2009
- +1 year = 8 May 2010
- -3 months = 8 February 2010
- +7 days = 15 February 2010
280 days past LMP is found by checking the day of the week of the LMP and adjusting the calculated date to land on the same day of the week. Using the example above, 8 May 2009 is a Tuesday. The calculated date (15 February) is a Friday; adjusting to the closest Tuesday produces 12 February, which is exactly 280 days past 8 May. The calculation method does not always result in a 280 days because not all calendar months are the same length, it does not account for leap years.
Parikh's Formula is a calculation method that considers cycle duration. Naegele's Rule assumes an average cycle length of 28 days, which is not true for everyone. EDD is calculated using Parikh's Formula by adding 9 months to LMP, subtracting 21 days, then adding duration of previous cycles.
In modern practice, calculators, reference cards, or sliding wheel calculators are used to add 280 days to LMP.
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