Human Prenatal Development Timeline

Nervous Nervous Cardiovascular Cardiovascular Musculoskeletal Musculoskeletal Early Events Early Events
Special Senses Special Senses Respiratory Respiratory Skin Skin Growth Parameters Growth Parameters
Movement Movement Gastrointestinal Gastrointestinal Endocrine Endocrine General General
Facial Facial Genitourinary Genitourinary Blood & Immune Blood & Immune "Gee Whiz" Facts "Gee Whiz" Facts

Unit 1:   The First Week 
Day 0Early Events Fertilization
Day 1 - Day 2Early Events First cell division - 24 to 30 hours
Day 4 - Day 5General Free-floating blastocyst
  Early Events Blastocyst
  Early Events Chest and back surfaces seen
Day 5Early Events Inner cell mass
Day 6 - 1 week, 5 daysEarly Events Embryo attaches to inside wall of mother's womb
1 weekEarly Events Placenta formation begins
Unit 2:   1 to 2 Weeks 
1 week, 1 dayEndocrine Pregnancy hormone (hCG) in mother's blood
1 week, 2 daysEarly Events Cells in womb engorged with nutrients
1 week, 5 daysEarly Events Implantation complete
1 week, 6 daysEarly Events Primitive streak
  Early Events Right & left sides, head end
Unit 3:   2 to 3 Weeks 
2 weeks, 3 daysEndocrine Portion of the thyroid
2 weeks, 4 daysCardiovascular Heart
3 weeksCardiovascular Blood vessels
  Cardiovascular Blood cells
  Respiratory Trachea or windpipe
  Special Senses Forebrain, midbrain & hindbrain
  Cardiovascular Tubular heart
Unit 4:   3 to 4 Weeks 
3 weeks, 1 dayCardiovascular Heart begins beating
  Cardiovascular Circulatory system function begins
3 weeks, 1 day - 4 weeksEarly Events Folding of the embryo
3 weeks, 3 daysSpecial Senses Neural tube closes (lower back)
4 weeksEarly Events Umbilical cord
  Cardiovascular Heart rate 113 beats/min
  Musculoskeletal Upper & lower limb buds
  Skin Skin transparent
 
Unit 5:   4 to 5 Weeks 
4 weeks, 4 daysSpecial Senses Cerebral hemispheres
4 weeks, 5 daysSpecial Senses Brain with five main sections
5 weeks"Gee Whiz" Facts Head is 1/3 of entire embryo
Unit 6:   5 to 6 Weeks 
6 weeksMovement Face withdraws from light touch around mouth
  Gastrointestinal Physiologic herniation begins
  Nervous External ear
  Blood & Immune Blood forming in liver
 
Unit 7:   6 to 7 Weeks 
6 weeks, 2 daysSpecial Senses Brainwaves
6½ weeksMusculoskeletal Hand movement
  Musculoskeletal Bone formation in collar bone
7 weeksMovement Leg movements
  Cardiovascular Heart rate peaks (165 to 170 beats/minute)
  Respiratory Hiccups
  Genitourinary Ovaries
Unit 8:   7 to 8 Weeks 
7 weeks, 3 daysNervous Eyelids grow rapidly
7½ weeksMusculoskeletal Knee joints
  Cardiovascular EKG pattern similar to adult
7 weeks, 4 daysMusculoskeletal Fingers completely separate
8 weeksSpecial Senses Handedness
  Respiratory Breathing motion
  Special Senses Brain highly complex
  Movement Complex response to touch
  Movement More frequent hand-to-face contact
  Genitourinary Urine production and release
 
Unit 9:   8 to 9 Weeks 
8½ weeksFacial Eyelids completely fused
9 weeksNervous Face, hands, & feet sense light touch
  Movement Grasps an object
  Movement Thumb sucking
  Movement Swallowing
  Endocrine Thyroid gland weighs 2 grams
  Movement Bends hip & knee if sole of foot touched
Unit 10:   9 to 10 Weeks 
9 weeks - 10 weeksGrowth Parameters Weight increases 75%
9 weeks, 4 daysSpecial Senses Yawns
10 weeksSkin Fingernails & toenails begin
  Skin Unique fingerprints
  Musculoskeletal Bone formation underway in most bones
Unit 11:   10 to 11 Weeks 
11 weeksFacial Nose & lips completely formed
  Genitourinary External genitalia clearly male or female
  Endocrine Thyroid gland weighs 12 grams
Unit 12:   11 to 12 Weeks 
12 weeksNervous Taste buds throughout mouth
  Musculoskeletal Upper limbs reach final proportion
  Gastrointestinal Bowel movements
Unit 13:   3 to 4 Months 
13 weeksNervous Most of body sensitive to touch
  Facial Tooth development
14 weeksFacial Fat deposits in cheeks
  Facial Jaw motion more frequent in females
  Movement Light touch to mouth evokes turn toward stimulus
15 weeksSkin Fat deposits in abdomen, back, kidneys & shoulders
16 weeksSkin Fat deposits upper & lower limbs
  Movement Mother first feels fetal movement
 
Unit 14:   4 to 5 Months 
18 weeksSkin Cream-like substance protects skin
20 weeksNervous Organ of hearing reaches adult size
  Skin All skin layers and structures
Unit 15:   5 to 6 Months 
20 weeks - 24 weeksNervous Eyelids separate, eyes open and close
21 weeks - 22 weeksGeneral Age of viability
 
Unit 16:   6 to 7 Months 
25 weeksNervous Responds to taste
26 weeksNervous Sense of smell
  Skin Additional fat deposits decrease wrinkles
26 weeks - 38 weeksSpecial Senses Brain weight increases 400% to 500%
27 weeksNervous Pupils react to light
Unit 17:   7 to 8 Months 
30 weeksRespiratory Breathing motions 30% to 40% of the time
Unit 18:   8 to 9 Months 
32 weeks - 36 weeksNervous Prenatal food affects newborn taste preferences
35 weeksMusculoskeletal Firm grip
 
Unit 19:   9 Months to Birth 
38 weeksGeneral Fetus initiates labor
  "Gee Whiz" Facts This timeline has more than 3.1 million configurations
  "Gee Whiz" Facts Heart beats 54 million times before birth