Janeen
Pregnancy Week by Week: What Happens in Each Trimester (Simple Guide)
Forty weeks sounds like forever — until you see what happens inside each one. A heartbeat at week 6. Fingerprints by week 12. First kicks around week 20. This is your pregnancy week by week map: the milestones that matter, what your body is doing, and which checkup happens when. (Not sure which week you're in? Calculate it here first.)
First trimester (weeks 1–13): the invisible marathon
Nothing shows on the outside; everything happens on the inside.
- Weeks 4–5: a poppy-seed-sized embryo implants. Hormones surge — tender breasts, fatigue, and the first hints of nausea.
- Week 6: the heart starts beating (~110-160 bpm — twice yours!).
- Weeks 8–10: nausea usually peaks. Baby graduates from embryo to fetus, with arms, legs and tiny fingers forming.
- Weeks 11–13: fingerprints form, and your dating/NT scan confirms how far along you are. Nausea starts easing.
Your checklist: start prenatal vitamins with folic acid, book your first prenatal visit (weeks 6–12), rest without guilt.
Second trimester (weeks 14–27): the golden months
Energy returns, the bump appears, and the best moment of pregnancy arrives:
- Weeks 16–18: baby can hear — your voice becomes their favorite sound. Talk and sing freely.
- Weeks 18–22: first movements! Gentle flutters at first, unmistakable kicks later. The anatomy scan checks every organ and (if you wish) reveals the sex.
- Weeks 24–28: the glucose screening test for gestational diabetes. Baby's lungs practice breathing; hiccups feel like tiny rhythmic taps.
Your checklist: book the anatomy scan, start the baby-names conversation, plan any travel now (it's the safest window), begin sleeping on your side by the end of this trimester.
Janeen shows exactly which week you're in — baby's fruit-size, length and weight, what's happening in your body, plus a kick counter, symptom diary and smart checkup reminders matched to your week. Free on iOS.
Download Janeen freeThird trimester (weeks 28–40): the home stretch
- Week 28: start daily kick counts — ten movements within two hours is the reassuring benchmark. Fewer than usual? Call your provider the same day.
- Weeks 30–34: baby opens their eyes, gains fat fast, and usually turns head-down. Braxton Hicks "practice" contractions appear — irregular and painless, unlike the real thing.
- Weeks 35–37: GBS swab test; pack the hospital bag; install the car seat.
- Weeks 39–40: full term. Watch for real labor signs: regular contractions that get closer and stronger, waters breaking, or the bloody show.
Your checklist: weekly checkups from week 36, birth plan printed, phone charged, and remember — only ~5% of babies arrive exactly on their due date.
Baby size cheat sheet
| Week | About the size of | Length / Weight |
|---|---|---|
| 8 | Raspberry 🫐 | 1.6 cm / 1 g |
| 12 | Lime 🍋 | 5.4 cm / 14 g |
| 20 | Banana 🍌 | 25 cm / 300 g |
| 28 | Eggplant 🍆 | 37 cm / 1 kg |
| 34 | Cantaloupe 🍈 | 45 cm / 2.1 kg |
| 40 | Watermelon 🍉 | 51 cm / 3.4 kg |
Week-by-week FAQ
How many weeks is each trimester?
First: weeks 1–13. Second: 14–27. Third: 28–40 (or until baby arrives — up to 42).
When should I start prenatal appointments?
First visit between weeks 6–12, then typically every 4 weeks until 28, every 2 weeks until 36, and weekly after that. Your provider may adjust the rhythm.
When do I stop counting in weeks and start months?
Honestly? Never — healthcare runs on weeks. Divide by 4.35 when relatives ask which month you're in.
The bottom line
Pregnancy makes sense when you follow it week by week: each week has its milestone, its symptom, and sometimes its checkup. You don't need to memorize any of it — Janeen tracks your exact week automatically and tells you what matters right now, from first heartbeat to hospital bag.