Pregnancy spans 40 weeks from the first day of your last menstrual period (LMP), though actual development starts at conception around week 2-3. This timeline tracks fetal growth from a single cell to a fully formed newborn, divided into three trimesters with key milestones, baby sizes, and maternal changes. Full-term ranges 37-42 weeks. Use our Pregnancy Calculator for week-by-week fetal updates or Due Date Calculator to estimate your EDD from LMP or ultrasound.
First Trimester: Weeks 1-13 (Foundation Phase)
Rapid cell division forms organs; highest miscarriage risk (15-20%). Baby grows from poppy seed to peach size.
| Weeks | Baby Size | Key Milestones | Mom’s Changes |
|---|---|---|---|
| 1-4 | Poppy seed | Fertilization, implantation, placenta starts | Missed period, fatigue, implantation spotting |
| 5-8 | Raspberry-kidney bean | Heartbeat (week 6), neural tube, limb buds | Nausea peaks, breast tenderness, frequent urination |
| 9-13 | Lime-peach | Organs form, fingerprints, movement begins | Energy returns, first ultrasound, small bump |
Care: Prenatal vitamins, first appointment by week 8.
Second Trimester: Weeks 14-27 (Growth and Viability)
“Honeymoon phase”—symptoms ease, baby viable by week 24 (50% survival). Triples in size.
| Weeks | Baby Size | Key Milestones | Mom’s Changes |
|---|---|---|---|
| 14-17 | Lemon-pear | Hair/nails, quickening (flutters week 16-20) | Energy boost, visible bump, heartburn |
| 18-22 | Banana-carrot | Gender visible, strong kicks, skin forms | Braxton Hicks, stretch marks, anatomy scan |
| 23-27 | Cauliflower-eggplant | Lungs surfactant, eyes open, fat layers | Glucose test, nesting, sharper movements |
Care: Anatomy ultrasound (week 18-20), 1 lb/week gain.
Third Trimester: Weeks 28-40 (Maturation and Delivery)
Baby gains 5+ lbs fat; discomfort increases as head engages pelvis.
| Weeks | Baby Size | Key Milestones | Mom’s Changes |
|---|---|---|---|
| 28-31 | Cabbage-squash | Brain surge, strongest kicks | Back pain, swelling, insomnia |
| 32-36 | Honeydew-cantaloupe | Lungs mature, head drops, weekly checks | Pelvic pressure, hemorrhoids, GBS test |
| 37-40 | Watermelon | Fully developed, positions for birth | Mucus plug, contractions, hospital bag ready |
Care: Biweekly visits from week 32; monitor movements.
Complete 40-Week Pregnancy Timeline Highlights
| Week Range | Fetal Development Focus | Maternal Milestones | Tests/Scans |
|---|---|---|---|
| 1-12 | Organogenesis | Symptoms peak | Dating ultrasound |
| 13-26 | Rapid growth | Feel movements | Anatomy scan |
| 27-40 | Weight gain, lung prep | Discomfort rises | Non-stress tests |
Size Progression: Poppy seed → watermelon (20 inches, 7-8 lbs at term).
Nutrition and Lifestyle by Trimester
- 1st: 1,800 cal/day, folic acid focus.
- 2nd: +340 cal, protein-rich.
- 3rd: +450 cal, iron/calcium boost.
Exercise 150 min/week; track with Pregnancy Calculator.
Warning Signs Throughout 40 Weeks
- Bleeding, severe pain, reduced movement.
- Vision changes, headaches (preeclampsia).
- Contractions before 37 weeks.
Why Track Your 40-Week Timeline?
Precise dating aligns screenings, detects issues early. Input LMP into Due Date Calculator or weeks into Pregnancy Calculator for custom milestones.
FAQs: 40 Weeks Pregnancy Timeline
Q: LMP vs. conception? 40 weeks LMP = 38 weeks from conception.
Q: Overdue? Safe to 42 weeks; induction common.
Q: Preterm viable? 24 weeks (50%), 34+ (95%).
Map Your 40-Week Journey Now
Enter LMP/EDD in Pregnancy Calculator or Due Date Calculator for personalized timelines, checklists, and tips. Share your week below!
This guide navigates your full pregnancy from conception to birth with confidence.