Two different methods can be used:

• Based on Last Menstrual Period (Naegele Formula):
  • Last menstrual period + 1 year + 7 days - 3 months
  • If cycle length is different from 28 days: + (cycle length - 28) days
• Based on Ultrasonography Date:
  • Pregnancy start = Ultrasonography date - pregnancy week
  • Estimated due date = Pregnancy start + 40 weeks

Trimesters:

• 1. Trimester: 0-12 weeks
• 2. Trimester: 13-26 weeks
• 3. Trimester: 27-40 weeks