Published July 14, 2026

Pregnancy Trimesters Explained: What Changes Each Stage

Pregnancy is typically divided into three trimesters, each roughly 13-14 weeks long, and each with its own developmental milestones and common experiences. Here's a general overview — always check with your own doctor or midwife for guidance specific to your pregnancy.

First trimester: weeks 1-13

The first trimester covers the earliest and most rapid development. By the end of week 13, your baby's major organs have begun forming, and by week 12 a heartbeat is typically detectable. This is also the stage most associated with fatigue and nausea ("morning sickness"), which for many people is at its most intense around weeks 6-10 and tends to ease heading into the second trimester, though timing varies widely.

Prenatal care usually begins in this window, often including a dating ultrasound that can refine your estimated due date beyond what a last-period-based calculation alone provides.

Second trimester: weeks 14-27

Often described as the most comfortable stretch of pregnancy for many people, the second trimester is when energy levels commonly improve and nausea typically fades. Around weeks 18-20, an anatomy ultrasound usually checks your baby's development in detail, and this is often when parents find out the baby's sex if they choose to. Many people start feeling fetal movement ("quickening") sometime between weeks 16-25.

Third trimester: weeks 28-40+

The final trimester is focused on rapid weight gain and final organ maturation, particularly the lungs. Braxton Hicks contractions (practice contractions) often start during this stage and can be mistaken for early labor. Appointments typically become more frequent — often every two weeks, then weekly as you approach your due date.

Only about 5% of babies are born exactly on their estimated due date — most arrive within a couple of weeks before or after, which is completely normal.

Track where you are right now

If you want a quick estimate of your current week and trimester based on your last period or conception date, use our due date calculator — it's a fast way to orient yourself between appointments, though your care provider's dating (especially from an early ultrasound) is the most accurate reference.