Pregnancy broken into weeks

wk 3 

brain, neural tube, heart, GI tract, arm, buds, leg buds

wk 4

limb buds, brain starts to differentiate

wk 5

heart beats, eyes and ears begin, muscle innervation, some CNS visible

wk 6

lungs, circulation, liver, primitive skeleton and brain develop, CNS formed, brain waves

wk 7

trunk straightens, extremities start to move, diaphragm formed, mouth forms (lips, tooth buds), toes, nipples, hair follicles

wk 8

intestines move to position, facial features

wk 10

3 cm long, jerking movements

wk13-16

lanugo on head, transparent skin, active motion, bones hardening, sucking motions, swallows amniotic fluid, finger and toes nails and weight incr 4x

wk 17-20

rapid brain growth, FHTS heard, venrix, caseosa appears, eyebrows and head hair start to grow, brown fat deposited, muscles develop

wk 21-24

grasp, startle reflexes, alveoli, surfactant

wk 25-28

5 in long, rapid brain development, eyelids functional, some nervous system control, fingerprints, fat, bone marrow starts to produce blood

wk 29-32

body fat, increased CNS control over body, breathing movements, starts storing Fe, Ca. Phos

wk 33-38

testes start to descend, lanugo starts to disappear, strong hand grasp, adding body fat

wk 37-42

surfactant, creases on hands and soles of feet, vernix resorb, placenta starts to age, anticipate delivery