1. What is the ACOG Pregnancy Dating Method?

The ACOG (American College of Obstetricians and Gynecologists) method calculates pregnancy due dates by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). This is based on Naegele's rule and is the standard method for estimating due dates in obstetrics.

2. How Does the Calculator Work?

The calculator uses the standard ACOG formula:

Where:

• LMP — First day of last menstrual period
• 280 days — Equivalent to 40 weeks gestation

Explanation: The calculation assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. The calculator also shows current gestational age based on today's date.

3. Importance of Accurate Pregnancy Dating

Details: Accurate pregnancy dating is crucial for proper prenatal care, timing of tests, monitoring fetal growth, and determining post-term pregnancies. It affects clinical decisions throughout pregnancy.

4. Using the Calculator

Tips: Enter the first day of your last menstrual period (LMP) in the format MM/DD/YYYY. The calculator will display your estimated due date and current gestational age.

5. Frequently Asked Questions (FAQ)

Q1: What if my cycles aren't regular?
A: For women with irregular cycles, an early ultrasound (first trimester) provides more accurate dating than LMP-based calculations.

Q2: How accurate is this method?
A: Only about 5% of women deliver on their exact due date. Most deliver within 2 weeks before or after the estimated date.

Q3: What if I know my conception date?
A: If conception date is known (e.g., with fertility treatments), due date is calculated as conception date + 266 days (38 weeks).

Q4: When should I get an ultrasound for dating?
A: First-trimester ultrasounds (especially 8-13 weeks) are most accurate for dating, with ±5-7 day accuracy.

Q5: What if my ultrasound due date differs from LMP date?
A: Clinicians typically use the ultrasound date if it differs from LMP by more than 5-7 days in first trimester.