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Pregnancy Weeks Calculation:
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Pregnancy weeks calculation determines how far along a pregnancy has progressed based on the first day of the last menstrual period (LMP). This is the standard method used by healthcare providers to estimate gestational age.
The calculator uses the standard pregnancy dating formula:
Where:
Explanation: The calculation counts the number of days between the LMP date and current date, then converts to weeks by dividing by 7.
Details: Accurate pregnancy dating is crucial for proper prenatal care, scheduling tests at the right times, monitoring fetal growth, and determining the estimated due date (typically 40 weeks from LMP).
Tips: Enter the first day of your last menstrual period and the current date (defaults to today). The calculator will show your pregnancy duration in weeks and days.
Q1: Why is pregnancy calculated from LMP rather than conception?
A: LMP is used because it's a definite date most women can recall, while conception date is often uncertain. In reality, conception typically occurs about 2 weeks after LMP.
Q2: What if my cycles aren't regular?
A: The LMP method assumes a 28-day cycle. If your cycles are significantly longer or irregular, an early ultrasound may be needed for accurate dating.
Q3: How accurate is this calculation?
A: The LMP method is accurate to within about ±2 weeks. First-trimester ultrasound can provide more precise dating if needed.
Q4: When should I see a doctor after a positive pregnancy test?
A: Most providers schedule the first prenatal visit around 8 weeks from LMP, but you should call earlier to schedule and discuss any immediate concerns.
Q5: What if I don't remember my LMP?
A: If you don't know your LMP, your provider will estimate gestational age based on physical exam and ultrasound measurements.