From the Guidelines
The expected date of delivery (EDD) for a patient with a last menstrual period (LMP) of 27 November 2024 is September 3,2025. This calculation is based on Naegele's rule, which is the standard method used in obstetrics to estimate the delivery date, as there is no direct evidence provided in the studies 1 that contradicts this method. The formula adds 7 days to the first day of the last menstrual period and then counts forward 9 months, or alternatively, counts back 3 months and adds 7 days. This method assumes a 28-day menstrual cycle and that conception occurred approximately 14 days after the start of the last menstrual period. It's worth noting that while LMP dating is commonly used, ultrasound measurement of crown-rump length (CRL) in early pregnancy provides an accurate estimate of gestational age, as mentioned in 1. However, in the absence of ultrasound dating, Naegele's rule is a reliable alternative. It's also important to note that this is an estimate, as only about 5% of women deliver exactly on their calculated due date, and most deliveries occur within two weeks before or after the EDD. Early ultrasound dating, particularly in the first trimester, can provide a more accurate EDD if there is uncertainty about the LMP date or if the patient has irregular menstrual cycles, but this is not directly relevant to calculating the EDD based on the provided LMP. Key points to consider in estimating the EDD include:
- The LMP date
- The assumption of a 28-day menstrual cycle
- The use of Naegele's rule for calculation
- The potential for variation in actual delivery date
- The option for more accurate dating using early ultrasound measurements, as discussed in 1.
From the Research
Calculating Expected Date of Delivery (EDD)
To calculate the EDD for a patient with a last menstrual period (LMP) of 27 November 2024, we can use Naegele's rule, which adds 7 days to the first day of the LMP and then adds 9 months 2.
- First day of LMP: 27 November 2024
- Add 7 days: 4 December 2024
- Add 9 months: 4 September 2025
Therefore, the expected date of delivery (EDD) would be approximately 4 September 2025.
Accuracy of LMP-Based EDD Calculation
However, it's essential to note that LMP-based EDD calculation may not always be accurate, especially if the patient has irregular menstrual cycles or is unsure of her LMP date 3, 4, 5, 6.
- A study published in the Belitung Nursing Journal found that LMP-based EDD calculation can contribute to adverse birth outcomes due to inaccuracies 3.
- Another study published in Midwifery found that midwives' calculations of EDD using LMP can be inconsistent and may lead to errors 4.
- A study published in Ugeskrift for laeger found that ultrasound dating does not lead to a more precise prediction of EDD for women with regular cycles and known LMP 2.
- A study published in The Indian Journal of Radiology & Imaging found that discordant dating of pregnancy by LMP and ultrasound can have implications for perinatal statistics 5.
- A study published in BMC Pregnancy and Childbirth found that early ultrasound and a Smartphone App were more accurate in predicting EDD compared to LMP recall 6.