How are pregnancy weeks counted?
Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. This means the first 2 weeks are technically before fertilization occurs.
Estimated due date
EDD = LMP + 280 days (40 weeks)
The three trimesters
First trimester (weeks 1-12)
- Formation of major organs
- Heartbeat detectable from week 6
Second trimester (weeks 13-26)
- First fetal movements (week 16-20)
- Gender can be determined
- Most comfortable period for the mother
Third trimester (weeks 27-40)
- Complete lung development
- Rapid weight gain
- Preparation for delivery
Did you know?
Only 5% of babies are born on their exact due date. A pregnancy is considered full-term between weeks 37 and 42.