A. By Last Menstrual Period (LMP)
The most common method is counting from the first day of your last menstrual period.
- Add 280 days (40 weeks) to this date to estimate your due date.
- This method assumes a regular 28-day cycle.
B. By Ultrasound Examination
Ultrasound is the most accurate way to estimate gestational age, especially in early pregnancy.
- First-trimester ultrasound measures the Crown-Rump Length (CRL).
- Later in pregnancy, measurements such as Biparietal Diameter (BPD) and Femur Length (FL) help refine the estimation.
C. By Physical Examination
An experienced OB-GYN can estimate gestational age by measuring fundal height and assessing other signs of pregnancy progression.