Learn about the stages of pregnancy by week: What happens to you and your fetus.
First Trimester (Weeks 1–12)
Weeks 1–2:
• Conception hasn’t occurred yet. Doctors count pregnancy from the first day of your last menstrual period (LMP).
• Ovulation and fertilization (sperm meets egg) typically happen around week 2 or 3.
Week 3 (Conception):
• Fertilized egg (zygote) forms and begins dividing rapidly.
• Implantation into the uterine lining occurs by the end of the week.
Week 4:
• Embryo is the size of a poppy seed.
• Placenta and amniotic sac start forming.
• Heart and circulatory system begin developing.
Week 5:
• Embryo is now the size of a sesame seed.
• Neural tube (future brain/spine) forms.
• Tiny heart starts beating (visible on ultrasound by week 6).
Week 6:
• Arm and leg buds appear.
• Eyes, ears, and brain develop rapidly.
Week 7:
• Embryo doubles in size (~1/2 inch).
• Hands and feet form (paddle-like).
• Facial features (nostrils, lenses of eyes) begin.
Week 8:
• Now called a fetus (size of a raspberry).
• All major organs form; bones start developing.
• Fingers/toes emerge (webbed).
Week 9–10:
• Fetus is ~1 inch long.
• Tail disappears; elbows bend.
• Teeth buds form; kidneys produce urine.
Week 11–12:
• Fetus is ~2.5 inches, weighs ~14g.
• Reflexes develop (sucking, kicking).
• Sex organs differentiate (but not yet visible on ultrasound).
Second Trimester (Weeks 13–27)
Week 13–16:
• Fetus grows to ~4–5 inches.
• Fine hair (lanugo) covers the body.
• Muscles strengthen; movements may be felt (quickening).
Week 17–20:
• Fetus is ~6–10 inches, weighs ~300g.
• Vernix (protective waxy coating) forms.
• Eyebrows, nails, and fingerprints develop.
• Gender may be visible on ultrasound.
Week 21–24:
• Fetus is ~12 inches, ~1–1.5 lbs.
• Lungs develop surfactant (helps breathing).
• Eyes open; responds to sounds and light.
Week 25–27:
• Rapid brain growth.
• Sleep/wake cycles establish.
• Survival outside the womb is possible (with intensive care).
Third Trimester (Weeks 28–40)
Week 28–32:
• Fetus is ~15–17 inches, ~3–4 lbs.
• Fat layers form (smoother skin).
• Bones harden (but skull stays soft for delivery).
• Kicks become stronger; may hiccup.
Week 33–36:
• Fetus is ~18–19 inches, ~5–6 lbs.
• Lungs mature; head may "engage" in pelvis.
• Lanugo starts shedding.
Week 37–40 (Full Term):
• Average size: ~19–21 inches, ~6–9 lbs.
• Organs are fully functional.
• Baby settles into birth position (head down).
• Birth typically occurs between 38–42 weeks.
Key Takeaways:
• First trimester: Major organs and structures form.
• Second trimester: Growth and refinement (movement, senses).
• Third trimester: Weight gain and lung/brain maturation.
• Advice for each stage of pregnancy
First Trimester (Weeks 1–12)
Physical Changes: Fatigue, nausea ("morning sickness"), breast tenderness, frequent urination, food aversions/cravings.
Baby’s Development: Organs, spine, and limbs form; heartbeat begins.
Advice:
1. Prenatal Care:
o Confirm pregnancy with a doctor and start prenatal vitamins (especially folic acid to prevent neural tube defects).
o Schedule your first prenatal visit (usually by week 8–10).
2. Manage Nausea:
o Eat small, frequent meals (ginger, crackers, or bland foods help).
o Stay hydrated; try lemon water or electrolyte drinks.
o Avoid strong smells.
3. Lifestyle Adjustments:
o Rest often—fatigue is normal due to hormonal changes.
o Avoid alcohol, smoking, raw fish, deli meats, and unpasteurized dairy.
o Limit caffeine (<200 mg/day).
4. Emotional Health:
o Mood swings are common; talk to a partner/friend or join a pregnancy group.
o Consider journaling to process emotions.
Second Trimester (Weeks 13–26)
Physical Changes: Energy returns, belly grows, "pregnancy glow," possible back pain, leg cramps, or nasal congestion.
Baby’s Development: Moves/kicks, hears sounds, develops fingerprints; gender may be detectable.
Advice:
1. Nutrition & Exercise:
o Focus on iron-rich foods (spinach, lean meats) and calcium (dairy, leafy greens).
o Stay active with prenatal yoga, swimming, or walking (unless restricted).
2. Body Changes:
o Wear comfortable, supportive clothing/maternity bras.
o Moisturize belly to reduce itchiness/stretch marks.
o Sleep on your side (left side improves circulation).
3. Bonding & Planning:
o Start prenatal classes (e.g., childbirth, breastfeeding).
o Announce pregnancy if desired and research childcare options.
4. Medical Checks:
o Anatomy scan (around week 20) checks baby’s growth.
o Monitor for warning signs (e.g., severe swelling, bleeding).
Third Trimester (Weeks 27–40+)
Physical Changes: Shortness of breath, heartburn, Braxton Hicks contractions, swelling, trouble sleeping.
Baby’s Development: Gains weight rapidly; lungs mature; settles into head-down position.