Updated June 17, 2026
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Pregnancy is divided into three trimesters: the first trimester runs from weeks 1 to 13, the second from weeks 14 to 27, and the third from week 28 to delivery at around week 40. Each trimester brings different developments for the baby and different experiences for the parent.
Trimester breakdown by week
| Trimester | Weeks | Key milestones |
|---|---|---|
| First | 1 to 13 | Implantation, heartbeat (week 6), major organ formation, risk of miscarriage highest |
| Second | 14 to 27 | Movement felt (week 18 to 22), anatomy scan (week 20), viability threshold approaches (week 24) |
| Third | 28 to 40 | Rapid weight gain, lungs mature, baby positions head-down, birth preparation |
First trimester (weeks 1 to 13)
The first trimester covers the earliest and most critical period of fetal development. The major organs, brain, spine, heart, and limbs form in these weeks. Nausea, fatigue, and breast tenderness are common, driven by rising hCG and progesterone levels. Most miscarriages, if they occur, happen in the first trimester, which is why many people wait until week 12 or 13 to share their news.
Second trimester (weeks 14 to 27)
Many people feel the second trimester is the most comfortable. Nausea typically eases, energy returns, and the baby's movements become noticeable, often called quickening, between weeks 18 and 22. The mid-pregnancy anatomy scan (around week 20) checks fetal development and can often reveal the sex. By week 24, a baby born prematurely has a chance of survival with intensive neonatal care.
Third trimester (weeks 28 to 40)
The third trimester is a period of rapid growth. The baby gains most of its birth weight during these weeks and the lungs continue to mature. Sleep becomes more difficult as the abdomen grows. Braxton Hicks contractions (practice contractions) may begin. Most babies position head-down in preparation for birth. Full term is considered 39 to 40 weeks, though 37 to 42 weeks is the normal birth range. Use the Due Date Calculator to find your current week and trimester.
These are general developmental stages. Your midwife or doctor will guide you through what is normal for your specific pregnancy at each stage.
Find your due date
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