Pregnancy Trimesters: What Changes Each Week in Your Body and Your Baby
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Track your pregnancy week
Open Pregnancy Calculator to see exactly which week and trimester you are in.
First Trimester: Weeks 1–12
Weeks 1–4: Implantation, hCG production begins, missed period. Weeks 5–8: Embryo forms major organs; heart begins beating (week 6); morning sickness peaks (weeks 6–9). Weeks 9–12: Embryo becomes a fetus; all major organs present though not fully developed; nuchal translucency screening at week 11–12.
Second Trimester: Weeks 13–27
Weeks 13–16: Fetus grows rapidly; gender visible by week 14–16. Weeks 17–20: Quickening (first felt movements) typically at week 18–20; anatomy scan at week 18–22. Weeks 21–27: Lung development; eyelids open; viability threshold at 22–24 weeks. Nausea typically resolves; energy returns.
Third Trimester: Weeks 28–40
Weeks 28–31: Brain development accelerates; baby can hear; Braxton Hicks contractions begin. Weeks 32–36: Baby gains weight rapidly (200g/week); head-down presentation by week 32–34 typically. Weeks 37–40: Lungs mature; baby considered full-term at 37 weeks. GBS testing at 35–37 weeks.
Using the Pregnancy Calculator
Enter your LMP date in Pregnancy Calculator to see your current gestational week, trimester, estimated due date, and key milestone dates. The calculator adjusts for cycle length if yours differs from the standard 28 days.
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Frequently Asked Questions
Try the workflow
Track your pregnancy week
Open Pregnancy Calculator to see exactly which week and trimester you are in.