A pregnant woman had her last LMP on 9 February 2018. Calculate the EDD by using Naegele's formula?

Central Institute of Psychiatry - 9 July 2022

Obstetrics & Gynaecology

Medium

Appeared in: Central Institute of Psychiatry - 9 July 2022

Explanation

Naegele's rule is a standard method used to calculate the Expected Date of Delivery (EDD).
The rule involves adding 9 months and 7 days to the first day of the Last Menstrual Period (LMP).
Step 1: Identify the first day of the LMP, which is 9 February 2018.
Step 2: Add 7 days to the date (9 + 7 = 16), resulting in 16 February 2018.
Step 3: Add 9 months to February, which results in November.
Step 4: The calculated EDD is therefore 16 November 2018.

Option A: This option results from an incorrect month calculation, likely by adding only 8 months to the LMP instead of 9.
Option C: This option results from an incorrect day calculation. The 9 months were added correctly, but the crucial 7 days were omitted.
Option D: This date is two days before the LMP. It is not a plausible EDD and does not involve any correct application of pregnancy dating rules.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of Expected Date of Delivery (EDD) using Naegele's Rule as background academic context rather than a clinical decision trigger.
Calculating the EDD is a fundamental part of antenatal care. It helps in scheduling prenatal visits, timing important screening tests (e.g., for aneuploidy, gestational diabetes), monitoring fetal growth, and planning for delivery.
Naegele's rule is a useful estimation but has limitations. It assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. For women with irregular cycles, a first-trimester ultrasound is the most accurate method for dating the pregnancy.
What if? If the woman's menstrual cycle was 35 days long instead of 28, ovulation would occur around day 21. Naegele's rule would estimate a due date that is about one week too early. In such cases, an early ultrasound would be used to establish a more accurate EDD.

How to Approach the Question

First, identify the key piece of information provided in the question: the Last Menstrual Period (LMP) is 9 February 2018.
Next, recall the formula for Naegele's rule, which is the standard method for calculating the Expected Date of Delivery (EDD). The formula is: LMP + 9 months + 7 days.
Apply the formula step-by-step. Start with the date: 9 February 2018.
Add 7 days to the day: 9 + 7 = 16. The date is now 16 February 2018.
Add 9 months to the month: February + 9 months = November. The year remains 2018.
The final calculated date is 16 November 2018. Match this result with the given options to find the correct answer.

Concept Tested & Keywords

Concept Tested: Calculation of Expected Date of Delivery (EDD) using Naegele's Rule.
Stem keywords: LMP, 9 February 2018, EDD, Naegele's formula
Lead-in keywords: Calculate
Clinical cues: Age/sex group narrows the expected diagnosis, intervention, or normal reference range.

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