GUIDE深度 · Deep dive
Pregnancy Trimesters Explained
Pregnancy is usually counted as 40 weeks and split into 1 to 13, 14 to 27 and 28 to 40. The due date is an estimate; trimesters are a convenient way to describe progress and schedule care.
The three ranges
First trimester is about weeks 1 to 13, second 14 to 27, third 28 to delivery.
Weeks are counted from the last period; an early ultrasound may adjust the due date.
Common checkpoints
Early: viability and NT; mid: anatomy scan and glucose test; late: fetal monitoring and GBS.
Exact tests and timing vary by region and clinician; follow the care plan.
FAQ
When does the second trimester start?
Commonly week 14; some sources count the end of week 13.
Do trimesters or the due date matter more?
The due date guides care; trimesters describe stage and do not change gestational age.