Gestational Age Formula:
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Gestational age is the common term used during pregnancy to describe how far along the pregnancy is. It is measured in weeks from the first day of the woman's last menstrual period (LMP) to the current date.
The calculator uses the standard formula:
Where:
Explanation: The calculation counts the number of days between the LMP and current date, then converts to weeks and days.
Details: Accurate gestational age determination is crucial for proper prenatal care, timing of tests and interventions, monitoring fetal growth, and determining due date.
Tips: Enter the first day of the last menstrual period (LMP) and the current date. The calculator will determine how many weeks and days pregnant this represents.
Q1: Why is gestational age calculated from LMP rather than conception?
A: LMP is typically more reliably known than conception date. By convention, pregnancy dating uses LMP + 2 weeks to account for the approximate time from LMP to conception.
Q2: What if I don't know my LMP or have irregular cycles?
A: An ultrasound measurement in early pregnancy (especially first trimester) can provide an accurate estimate of gestational age.
Q3: How accurate is this calculation?
A: For women with regular 28-day cycles who conceive around day 14, this method is accurate. Variations occur with irregular cycles or conception at different cycle times.
Q4: What is Naegele's rule for due date?
A: The standard due date is calculated as LMP + 1 year - 3 months + 7 days (approximately 40 weeks from LMP).
Q5: How does this differ from fetal age?
A: Fetal age (conceptual age) is about 2 weeks less than gestational age, as it counts from conception rather than LMP.