embryonic & fetal development chart

Embryonic & fetal development

What major structure forms at week 3?

Neural tube forms (becomes spinal cord); heart and GI tract begin development.

What key event happens at week 4?

Neural tube closes; 4-chamber heart forms; brain differentiates; limb buds appear; lungs, kidneys, liver, genitalia begin forming.

When does the fetal heart begin beating regularly?

Week 5.

What is a key milestone of week 6?

Fetal circulation established; brain waves detectable; liver produces RBCs; primitive skeleton forms.

What develops in week 7?

Ear begins forming; toes/elbows visible; limb movement; diaphragm formed; tooth buds appear.

What defines week 8 of development?

Organogenesis complete; eyelids form (sealed); placenta functioning; genital differentiation begins; intestines rotate.

When is fetal sex identifiable?

Around week 12.

What happens to movement in weeks 9–12?

Fetus kicks, swallows, and moves; urine production begins.

What proportion of body size is the head at this stage?

Nearly half the fetal size.

What is quickening?

First fetal movement felt by pregnant person (weeks 16–20).

What develops in weeks 13–16?

Fingernails/toenails; bone hardening; sucking motions; external genitalia visible.

What appears on fetus at 17–20 weeks?

Lanugo, vernix caseosa, eyebrows, scalp hair.

When can fetal heart tones be heard with a stethoscope?

Around 17–20 weeks.

What is a key fetal fat development at this stage?

Brown fat forms for temperature regulation.

What lung development begins at 21–24 weeks?

Alveoli formation and surfactant production begins.

What reflexes are present at this stage?

Startle and hand grasp reflexes.

What is the viability milestone?

Around 24 weeks (fetus may survive with intensive support).

When do eyelids open?

Weeks 25–28.

What sensory abilities develop at this stage?

Responds to light and sound; can open eyes and suck thumb.

What major circulatory change occurs?

Bone marrow takes over RBC production.

What major development occurs in weeks 29–32?

Rapid brain development and increased body fat.

What lung activity is seen?

Rhythmic breathing movements (lungs still immature).

What reflex is present?

Pupillary light reflex.

When is the fetus considered full term?

39 weeks.

What happens to lanugo?

It disappears.

What lung-related change occurs near term?

Lungs mature and surfactant increases.

What immune protection does the fetus receive?

Maternal antibodies cross placenta.

What position does the fetus usually assume near term?

Head-down (vertex) position.