From the Research
Based on a last menstrual period (LMP) of December 30,2024, the estimated due date (EDD) would be October 6,2025, but this calculation should be verified with an early ultrasound for greater accuracy, as studies have shown that ultrasound dating is more reliable than LMP dating 1.
Calculation Method
The calculation uses Naegele's rule, which adds 7 days to the first day of the last menstrual period and then counts forward 9 months. Pregnancy typically lasts about 40 weeks (280 days) from the first day of the last menstrual period.
Importance of Verification
It's essential to note that this is just an estimate, as only about 5% of babies are actually born on their calculated due date. Most deliveries occur within two weeks before or after the EDD. This calculation assumes a regular 28-day menstrual cycle. If menstrual cycles are consistently longer or shorter than 28 days, the EDD might need adjustment.
Recommendation for Accuracy
An ultrasound in the first trimester can provide a more accurate due date, especially if there's uncertainty about the LMP date or if menstrual cycles are irregular, as supported by studies comparing the accuracy of LMP and ultrasound in predicting delivery dates 2, 3, 4, 5.
Key Points
- LMP dating can be less accurate due to variability in menstrual cycle length and the possibility of delayed ovulation.
- Ultrasound dating, particularly in the first trimester, offers a more precise estimation of gestational age and expected delivery date.
- Combining LMP with ultrasound scanning can help improve the accuracy of gestational age assignment and reduce the misclassification of preterm and postterm births.