A Prenatal Development Timeline

First Month

• Fertilization takes place, and a new life begins (day 1).
• Cell division takes place, and the cells begin to specialize into different tissues (week one and two).
• New life is implanting in the lining of the womb (4-10 days).
• Heart begins to beat (about 21 days).
• Foundation of the brain and nervous system established (third week).
• Muscle tissue begins forming; arms and legs begin to form; eye and ear formation is in early stages (four weeks).
• New life is about the size of an apple seed – not yet ¼ of an inch (four weeks).

Image Credit: LunarCaustic Flickr

Second Month

• Hands and feet start to develop (five weeks).
• Brain waves have been recorded (about 6 weeks).
• Eyes begin to darken (six weeks).
• Simple movements have begun (six weeks).
• Movements become more purposeful (eight weeks).
• Eyelids begin to seal over (eight weeks).
• The stomach and digestive organs are developing (eight weeks).
• Permanent kidneys have formed (eight weeks).

Third Month

• All major organ systems have been established (nine weeks).
• Facial features are more well formed (nine weeks).
• Early fingerprints, fingernails and toenails have formed (10 weeks).
• Breathing movements have been detected (10 weeks).
• The cerebral cortex of the brain has started to from (11 weeks).
• The unborn child can open and close its mouth – and swallow (by 12 weeks).
• The unborn child can make a fist, touch its face and turn its head (by 12 weeks).
• Sex of the new life can be visually determined (by 12 weeks).
• The unborn child is approaching four inches in length (by about 12 weeks).

Fourth, Fifth, and Sixth Months 

• A period of rapid growth takes place (thirteen to sixteen weeks).
• Bones are beginning solidifying process (thirteen to sixteen weeks).
• Arm and leg movements are becoming much more coordinated (fourteen weeks).
• The unborn child can detect sound (seventeenth to nineteenth weeks).
• “Quickening” takes place, the mother can feel movement (eighteen weeks).
• Hair and eyebrows have formed (twenty weeks).
• Rapid eye movements have been detected (twenty-one weeks).
• All parts of the eye, and eyelashes have developed (twenty-four weeks).
• The unborn child is about nine inches in length (twenty-four weeks).

Seventh Month Through Birth

• Hearing has become more well developed (twenty-fifth to twenty-eight week).
• Eyelids have opened (twenty-six weeks).
• The lungs have become more mature (twenty-sixth to twenty-ninth weeks).
• Breathing is more rhythmic (twenty-sixth to twenty-ninth weeks).
• Skin is becoming smoother as a layer of fat for insulation increases in the last three weeks of pregnancy.
• The baby weighs about six to nine pounds and is ready for life outside the womb!!

Sources: Keith Moore, The Developing Human, 2020. MedlinePlus: National Institutes of Health / U.S.
National Library of Medicine.

(Note: Times given refer to development after conception. As with all individuals, some variation may
exist in time of development. Lengths are measured from top of the head to the lower trunk. Other
sources available upon request.)