7 1/2 week embryo, 7.5 week embryo, seven and a half week embryo

Interactive Prenatal Development Timeline

[All ages refer to time since fertilization] [Features] [Help] [Tutorial] [Print preview] [PDF]

Choose level of difficulty:
Beginner

BODY SYSTEMS SELECTION MENU

Select/Clear All


Show Footnotes Show Bibliography	Include related events from other systems	Page Language:	Additional Language:

Go to Weeks:

0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-16 16-20 20-24 24-28 28-32 32-36 36-38

	Unit 1: The First Week
	Play Movie	See Snapshots

(Day 0): Embryonic period begins (Day 1): Embryo is spherically shaped with 12 to 16 cells (Day 1 - Day 1): Fertilization - development begins with a single-cell embryo!!! (Day 2): Zygote divides into two blastomeres (24 – 30 hours from start of fertilization) (Day 4): Free floating blastocyst Inner cell mass See where the back and chest will be (Day 6): Embryo attaches to wall of uterus (1 week): Placenta begins to form Less Events...

	Unit 3: 2 to 3 Weeks
	Play Movie	See Snapshots

(2 weeks, 1 day): Rostral-caudal orientation (2 weeks, 2 days): Three types of blood-forming cells in yolk sac (2 weeks, 4 days): Foregut, midgut, and hindgut Brain is first organ to appear (2 weeks, 6 days): Beginnings of the heart can be seen Forebrain, midbrain, and hindbrain Three main divisions of brain (3 weeks): Blood and blood vessels

	Unit 5: 4 to 5 Weeks
	Play Movie	See Snapshots

(4 weeks, 4 days): Brain: Cerebral hemispheres appear and begin rapid growth (4 weeks, 5 days): Blood vessels penetrate diencephalon Brain with five main sections First nerve fibers (5 weeks): Lobar pattern mimics adult pattern Pacemaker cells Head is one third of entire embryo

	Unit 7: 6 to 7 Weeks
	Play Movie	See Snapshots

(6 weeks, 2 days): Elbow regions sometimes identifiable Humerus, radius, and ulna Submandibular gland primordia Brainwave activity has begun (6½ weeks): The hands begin to move Bones first form in the collar bones and lower jaw (6 weeks, 5 days): Arms point forward Beginnings of occipital and sphenoid bones (6 weeks, 6 days): Cloacal membrane ruptures (7 weeks): Head rotates Leg movements Ovaries Hiccups The heart has four chambers and is nearly complete. The heart rate peaks at 165 to 170 beats per minute. Less Events...

	Unit 9: 8 to 9 Weeks
	Play Movie	See Snapshots

(8 weeks, 1 day): Fetal Period Begins (8½ weeks): Eyelids completely fused (9 weeks): Bends hip & knee if sole of foot touched Drinking fluid is becoming routine Sucking the thumb The young fetus now sighs, stretches, moves the head, opens the mouth, and moves the tongue Thyroid gland weighs 2 grams Face, hands, and feet sense light touch (9 weeks - 10 weeks): My weight will rise more than 75% this week Less Events...

	Unit 11: 10 to 11 Weeks
	Play Movie	See Snapshots

(10½ weeks): Volar and plantar pads regress (11 weeks): Nose & lips completely formed Now you can tell if your baby is a girl or a boy! Thyroid gland weighs 12 grams Intestines absorb water & glucose

	Unit 13: 3 to 4 Months
	Play Movie	See Snapshots

(13 weeks): Teeth are growing Most of body sensitive to touch (14 weeks): Girls move their jaws more than the boys do Light touch to mouth evokes turn toward stimulus Cerebellum resembles adult structure Fat deposits in cheeks (15 weeks): Body fat emerges throughout the body (16 weeks): Quickening Fat deposits upper & lower limbs Less Events...

	Unit 15: 5 to 6 Months
	Play Movie	See Snapshots

(21 weeks - 22 weeks): If born prematurely from this point on, survival is possible (23 weeks): Brain weight 100 grams

	Unit 17: 7 to 8 Months
	Play Movie	See Snapshots

(30 weeks): Breathing motions are common even though there is no air in the womb Head circumference 30 cm (32 weeks): Esophagus: Lower esophagus muscles functional (32 weeks - 36 weeks): Prenatal food affects newborn taste preferences

	Unit 19: 9 Months to Birth
	Play Movie	See Snapshots

(37 weeks): Fetus drinks an estimated 15 oz (or 450cc) of amniotic fluid/day (38 weeks): Heart beats 54 million times before birth Brain weight 350 grams Fetus initiates labor Head circumference 35 cm Time to be born!

Fertilization

Week 1 ends

Play Movie - 1 to 2 weeks, implantation and HCG

Week 2 ends

Play Movie - 2 to 3 week embryo, amnion, germ layer

Week 3 ends

Play Movie - 3 to 4 week embryo, folding of the embryo

Week 4 ends

Play Movie - 4 to 5 week embryo, The Heart in Action

Week 5 ends

Play Movie - 5 to 6 week embryo, hand plates develop

Week 6 ends

Play Movie - 6 to 7 week embryo, hand movement

Week 7 ends

Play Movie - 7 to 8 week embryo, fingers, toes

Week 8 ends

Play Movie - 8 to 9 week fetus, reflexive movement

Week 9 ends

Play Movie - 9 to 10 week fetus, sucking, swallowing

Week 10 ends

Play Movie - 10 to 11 week fetus, eyes roll, yawns

Week 11 ends

Play Movie - 11 to 12 week fetus, nails, fingerprints

Month 3 ends

Play Movie - 3 to 4 month fetus, the rooting reflex

Month 4 ends

Play Movie - 4 to 5 month fetus, bronchial tree

Month 5 ends

Play Movie - 5 to 6 months fetus, responds to sound

Month 6 ends

Play Movie - 6 to 7 month fetus, response to light

Month 7 ends

Play Movie - 7 to 8 month fetus, behavioral states

Month 8 ends

Play Movie - 8 to 9 month fetus, firm hand grasp

Month 9 ends

Birth

168 events on this timeline

Click any picture to see more!

	Unit 2: 1 to 2 Weeks
	Play Movie	See Snapshots

(1 week, 1 day): Positive pregnancy test (1 week, 2 days): Cells in womb engorged with nutrients (1 week, 5 days): Implantation complete Yolk sac

	Unit 4: 3 to 4 Weeks
	Play Movie	See Snapshots

(3 weeks, 1 day): Respiratory outgrowth Circulatory system function begins Heart begins beating Tubular heart begins folding Umbilical arteries Umbilical veins (right and left) Body cavities (3 weeks, 3 days): Liver Membrane between future mouth and throat may begin to rupture (3 weeks, 5 days): First part of pancreas Lung bud Descending aorta Lowermost spinal cord formation begins Neural tube closes (lower back) Upper limb primordium at level of somites 8 to 10 Progressively C-shaped embryo (4 weeks): Skin is so thin, you can see through it! Esophagus primordia Pancreas: Ventral pancreas Pharynx Small & large intestines Lungs begin filling chest cavity Trachea Circulatory system "well established" Functioning two-chamber heart Heart rate (about) 113 beats/min Fourth ventricle Cervical flexure Limb buds - the first sign of arms and legs Umbilical cord emerging Upper and lower limb buds Less Events...

	Unit 6: 5 to 6 Weeks
	Play Movie	See Snapshots

(5 weeks, 2 days): All cranial nerves identifiable (5½ weeks): Initial tooth formation (5½ weeks - 6 weeks): Subtle movement begins (5 weeks, 6 days): Primordial vermiform appendix (6 weeks): Face withdraws from light touch around mouth Blood forming in liver Tooth buds (primary teeth) Intestines fill base of umbilical cord

	Unit 8: 7 to 8 Weeks
	Play Movie	See Snapshots

(7 weeks, 1 day): Upper limbs with slightly flexed elbows Sacrocaudal spinal cord formation (secondary neurulation) complete (7 weeks, 1 day - 8 weeks): Stomach: Folds in stomach wall (7 weeks, 2 days): Arteries and veins of heart complete (7 weeks, 3 days): The knee joints have arrived Eyelids growing rapidly (7½ weeks): Fingertips thicken EKG pattern similar to adult (7 weeks, 4 days): The fingers are free (7 weeks, 5 days): Bone-forming cells emerge Hands can reach one another and fingers can overlap (8 weeks): Complex response to touch More frequent hand-to-face contact Urine production and release Occasional breathing motions begin Blood supply to the brain closely resembles adult pattern Ear drum "The hindbrain "presents striking resemblance to that of the newborn." Brain represents 43% of embryo Right- and left-handedness emerges Embryonic Period Ends Less Events...

	Unit 10: 9 to 10 Weeks
	Play Movie	See Snapshots

(9 weeks, 4 days): Yawns (10 weeks): Palatine tonsils Fingernails and toenails begin to grow! Three-layered epidermis Tiny unique fingerprints have arrived! Now, all the bones are getting harder Tooth buds (secondary teeth)

	Unit 12: 11 to 12 Weeks
	Play Movie	See Snapshots

(12 weeks): Many different hormones are present in pituitary gland Upper limbs reach final proportion Bowel movements Liver: Bile production begins There are taste buds all over the mouth Head circumference 10 cm

	Unit 14: 4 to 5 Months
	Play Movie	See Snapshots

(18 weeks): Cream-like substance protects skin Sweat glands (19 weeks): Melanin production Daily cycles in biological rhythms (20 weeks): All skin layers and structures Hearing and responding to sound begins Hearing and responding to sound begins Head circumference 20 cm (20 weeks - 24 weeks): Eyelids separate, eyes open and close Less Events...

	Unit 16: 6 to 7 Months
	Play Movie	See Snapshots

(25 weeks): Intestinal lining contains all adult cell types The ability to taste (26 weeks): Additional fat deposits decrease wrinkles The ability to smell has arrived (26 weeks - 38 weeks): Brain weight increases 400% to 500% (27 weeks): Pupils react to light

	Unit 18: 8 to 9 Months
	Play Movie	See Snapshots

(35 weeks): Firm grip (36 weeks): Brain weight 300 grams

Nervous	Cardiovascular	Muscular	Early Events
Special Senses	Respiratory	Skeletal	General
Blood & Immune	Gastrointestinal	Endocrine	Growth Parameters
Skin/Integument	Renal/Urinary	Reproductive	Movement