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NHS Estimated Due Date Calculation:
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The NHS Estimated Due Date (EDD) calculation is a standard method used to determine the expected delivery date of a pregnancy. It is based on Naegele's rule, which adds 280 days (40 weeks) to the first day of the last menstrual period.
The calculator uses the NHS standard formula:
Where:
Explanation: This calculation assumes a regular 28-day menstrual cycle and ovulation occurring on day 14. The 280 days represents the typical human gestation period from the first day of the last menstrual period.
Details: Accurate EDD calculation is crucial for prenatal care scheduling, fetal growth monitoring, timing of prenatal tests, and planning for delivery. It helps healthcare providers track pregnancy progress and identify potential complications.
Tips: Enter the first day of your last menstrual period in the date field. Ensure the date is accurate as this forms the basis for all subsequent pregnancy dating and clinical decisions.
Q1: How accurate is the EDD calculation?
A: The EDD is an estimate - only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the calculated date.
Q2: What if my menstrual cycle is irregular?
A: For women with irregular cycles, the EDD may be adjusted based on early ultrasound dating, which is more accurate in the first trimester.
Q3: Can the EDD change during pregnancy?
A: Yes, EDD may be adjusted after dating scans, especially if there's a significant difference between LMP-based dating and ultrasound measurements.
Q4: Why 280 days instead of 9 months?
A: Pregnancy is calculated in weeks (40 weeks) rather than calendar months because months have varying lengths. 280 days equals 40 weeks of gestation.
Q5: What is the margin of error for EDD?
A: The EDD is accurate to within ±5 days when based on LMP with regular cycles, and ±3-5 days when confirmed by first-trimester ultrasound.