Baby development during pregnancy progresses in distinct stages each month, marked by rapid and complex growth and maturation of organs and systems.
Month 1 (Weeks 1–4)
- Fertilized egg implants in uterus; amniotic sac and placenta form
- Early embryo begins developing brain, spinal cord, heart, and basic facial features
- Heart starts to beat
- Baby is about the size of a grain of rice (6–7 mm)
Month 2 (Weeks 5–9)
- Facial features become more defined; eyes, ears, nose form
- Limb buds appear; cartilage starts to form bones
- Major organs (brain, digestive tract, heart) develop rapidly
- Baby reaches about 1 inch (2.54 cm) length and weighs near 1/3 ounce (9.5 g)
Month 3 (Weeks 10–14)
- All major organs and body structures formed
- Hands, feet, fingers, and toes well defined
- Nails, external ears, teeth begin developing
- Baby is about 4 inches long and weighs around 1 ounce (28 g)
- Risk of miscarriage decreases significantly
Month 4 (Weeks 15–19)
- Hair, eyelashes, nails develop
- Baby begins moving and stretching; movements may be felt later
- Reproductive organs distinguishable on ultrasound
- Baby grows to about 6 inches and weighs around 4 ounces (113 g)
Month 5 (Weeks 20–24)
- Lanugo (fine body hair) covers baby; vernix caseosa (protective coating) forms on skin
- Baby’s kicks usually become noticeable
- Baby reaches about 10 inches and weighs 0.5 to 1 pound
Month 6 (Weeks 25–30)
- Skin is translucent and wrinkled; eyelashes and fingerprints develop
- Eyes may open and respond to sounds
- Baby grows to 12 inches and nearly 2 pounds
Month 7 (Weeks 26–29)
- Rapid growth continues; fat accumulates under skin
- Hearing is fully developed
- Baby is about 14 inches long and weighs 2 to 4 pounds
Month 8 (Weeks 30–34)
- Brain development accelerates; lungs mature but not fully developed
- Baby can see and respond to stimuli, movement increases
- Length about 18 inches; weight around 5 pounds
Month 9 (Weeks 35–40+)
- Lungs fully mature for breathing after birth
- Reflexes like blinking, grasping, and head turning develop
- Baby moves less, preparing for birth positioning
- Length 18–20 inches; weight typically 7 pounds or more
Summary
Baby development progresses from a tiny embryo with basic structures in the first month to a fully-formed, increasingly active fetus in later months, rapidly gaining size, fat, brain complexity, and organ function. Each month brings important milestones critical for survival and healthy growth.
