Accurate history-taking is an integral part of the antenatal booking assessment. Knowing the expected day of delivery of fetal age is important to clinicians and expectant mothers when planning care. One aspect of this is to determine the woman’s menstrual history and the date of her last menstrual period (LMP). This is to enable calculation of the expected date of delivery using Naegele tule as shown below. By predicting accurately the estimated date of delivery (EDD), evaluation of fetal growth and unnecessary early induction of labor can be monitored.

The length of pregnancy is calculated at 280 days from the first day of the LMP. However, there are various factors that will affect the length of pregnancy and the calculation of the EDD: –

Ever heard that the gestation period of a human being is 9 months or 40 weeks? This is a generalization because various factors can affect expected day of delivery.

* The length of the menstrual cycle: Some people have 28, 30 or 33 days cucles. Others even have 25 days cycle whle others are never consistent.

* Conception within three months of discontinuing the contraceptive pills:

* Conception while taking the contraceptive pill

* Conception when an intrauterine device is in situ

* When the last bleed is calculated as a menstrual period when it is an implantation bleed

* In vitro fertilization when the day of conception is known.

When taking details of a woman’s menstrual history, the following questions should be asked:

* At what age when menstruation started

* Regularity of menstrual bleeds

* Frequency of menstrual bleeds

* Length of menstrual bleeds, especially the last one.

Gestational age and calculation of EDD by LMP is calculated according to Naegele’s rule. That is, counting forwards by nine months and adding seven days from the first day of the LMP or by adding a year, counting backwards by three months and adding seven days.

It is important to calculate using the length of the menstrual cycle. The latter calculation is based on a 28-day cycle. For a 33-day cycle, the calculation is to add nine months, then seven days then five days.

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Vanessa Egnor says

If a persons LMP was 3/05/11 how do you do the nagele’s rule? What month, day, year do you burrow from. Please send me a step by step written example. I need to see the math actually being done. Thank you.

domz tolentino says

I still remember what i’ve learned in the school, If the LMP is within the months of January to March, the formula is this: +9 + 7 (wherein 9 is the month and 7 is the day)

so in your example: March 5,2011:

03-05-11

+ 9+ 7

_________

12-12-11 = this is the EDD

If the LMP is from April to December, the formula is: minus 3 plus 7 plus 1 ( -3+7+1)

Hope it helps………..

macoy says

yeah.. that’s right sir. I still remember that. 🙂