Pregnancy by trimester: a plain-English guide
What changes in each trimester and which appointments and screenings tend to land where.
5 min readReviewed May 1, 2026
Quick answer
Trimesters split pregnancy into three rough phases: weeks 1–13 (first), 14–27 (second), and 28–birth (third). Each has its own milestones and screenings.
First trimester (weeks 1–13)
- Confirmation of pregnancy and dating ultrasound.
- Early symptoms: fatigue, nausea, breast changes.
- Highest risk window for miscarriage; the risk drops sharply after 12 weeks.
Second trimester (weeks 14–27)
- Anatomy scan around 18–22 weeks.
- Often the most comfortable trimester — early symptoms ease.
- Movement ("quickening") usually felt by 20 weeks.
Third trimester (weeks 28–birth)
- Glucose screening and group B strep testing.
- More frequent prenatal visits, weekly near the end.
- Term begins at 37 weeks; "full term" is 39+0 to 40+6.