Embryoic and fetal Development

Week 3

Neural tube forms, which later becomes the spinal cord.

Beginning development of the heart

Beginning development of the gastrointestinal tract

week 4

Neural tube closes.

Four chambers of heart formed

Brain differentiates.

Limb buds grow and develop.

Diaphragm and lungs begin to form.

Stomach, pancreas, liver, urinary tract, and genitalia begin to form

Week 5

Heart now beats at a regular rhythm.

Beginning structures of eyes and face

Some cranial nerves are visible.

Muscles innervated

Week 6

Fetal circulation established

Liver produces red blood cells.

Further development of the brain

Primitive skeleton forms.

Central nervous system forms.

Brain waves detectable

Week 7

Straightening of trunk, characteristic C shape

Beginning of ear development

Nipples and hair follicles form.

Elbows and toes visible

Legs move

Diaphragm formed

Mouth with lips and early tooth buds

Week 8

Rotation of intestines

Facial features continue to develop.

Heart development completes.

Resembles a human being

Penis, urethra, scrotum (male) or clitoris and labia (female) begin to form.

Placenta is working.

Eyelids form and grow but are sealed shut.

Organogenesis is complete.

Week 9-12

Sexual differentiation continues.

Buds for all 20 temporary teeth laid down

Digestive system shows activity.

Head makes up nearly half the fetus size.

Face and neck are well formed.

Urogenital tract completes development.

Red blood cells are produced in the liver.

Urine begins to be produced and excreted.

Fetal sex can be determined by week 12.

Limbs are long and thin.

Digits are well formed.

Fetus moves, kicks, and swallows.

Weeks 13-16

Fetal skin is almost transparent.

Bones become harder.

Fetus makes active movement.

Sucking motions are made with the mouth.

Amniotic fluid is swallowed.

External genitalia are recognizable.

Fingernails and toenails present

Formation of pinna

Weight quadruples.

Fetal movement (also known as quickening) detected by pregnant person

Weeks 17-20

Rapid brain growth occurs.

Fetal heart tones can be heard with stethoscope.

A fine hair called lanugo develops on the head.

Kidneys continue to secrete urine into the amniotic fluid.

Vernix caseosa, a white greasy film, covers the fetus.

Eyebrows and head hair appear.

Brown fat deposited to help maintain temperature

Nails are present on both fingers and toes.

Muscles are well developed.

Weeks 21-24

Eyebrows and eyelashes are well formed.

Fetus has a hand grasp and startle reflex.

Alveoli forming in lungs

Skin is translucent and red.

Eyelids remain sealed.

Lungs begin to produce surfactant.

Weeks 25-28

Fetus reaches a length of 15 in.

Brow formation

Rapid brain development

Eyelids open and close.

Nervous system controls some functions.

Fingerprints are set.

Subcutaneous fat is visible under the skin.

Blood formation shifts from spleen to bone marrow.

Fetus usually assumes head-down position.

Fetus responds to light and sound.

Fetus can open and shut eyes and suck thumb

Weeks 29-32

Rapid increase in the amount of body fat

Increased central nervous system control over body functions

Rhythmic breathing movements occur.

Lungs are not fully mature.

Pupillary light reflex is present.

Fetus stores iron, calcium, and phosphorus.

Weeks 33-39

Testes are in scrotum of male fetus.

Lanugo begins to disappear.

Has strong hand grasp reflex

Increase in body fat

Earlobes formed and firm

Fingernails reach the end of fingertips.

Small breast buds are present on both sexes.

Pregnant person supplies fetus with antibodies against disease.

Fetus is considered full term at 39 weeks.

Fetus fills uterus and moves to a head-down position.