Prenatal Milestones

A quick week-by-week breakdown of baby's development in utero.

Week Three

Fertilization happens as the egg is making its way to the uterus. Chromosomes are assembled at fertilization, which dictate baby's sex, hair and eye color.

Week Four

The fertilized egg implants in the uterus. Cells continue dividing.

Week Five

Baby's brain, spinal cord and heart begin forming.

Week Six

Baby's heart starts beating.

Week Seven

Baby's other organs (kidney, liver, lungs, digestive system) begin forming.

Week Eight

What was an embryo becomes a fetus this week. Face begins to form.

Week Nine

Reproductive organs begin forming. Baby may visibly move during an ultrasound.

Week Ten

Tail and finger-webbing disappear. Face is well-defined.

Week Eleven

Fingernails begin forming. Eyes are fused shut, but are developing irises.

Week Twelve

Tooth buds, fingers and toes are formed. Baby looks like a tiny person.

Week Thirteen

Placenta takes over producing hormones. Baby becomes more proportional (body starts growing to catch up to its big head).

Week Fourteen

Fingerprints are developed. Baby grows lanugo (hair) to keep warm. May start sucking thumb.

Week Fifteen

Baby is moving, making fists, and making facial expressions.

Week Sixteen

Eyes are moving and may be able to perceive some light.

Week Seventeen

Lungs are breathing amniotic fluid. Hair, eyebrows and eyelashes are growing in.

Week Eighteen

Ears are developed enough to begin hearing.

Week Nineteen

Baby is now coated in vernix, which protects their skin from the amniotic fluid.

Week Twenty

Baby can hear and may respond to sounds.

Week Twenty-one

Intestines are producing meconium.

Week Twenty-two

Reproductive organs are placed correctly.

Week Twenty-three

Lungs mature. Viability begins.

Week Twenty-four

Fat continues to develop. Viability begins.

Week Twenty-five

Skin starts becoming opaque.

Week Twenty-six

Eyes can open and shut.

Week Twenty-seven

Baby has a schedule of alternating sleep and wakefulness.

Week Twenty-eight

Baby can blink, cough and hiccup.

Week Twenty-nine

Becomes more aware of sounds, light, and pressure/touch.

Week Thirty

Brain begins to wrinkle.

Week Thirty-one

Can process input from all five senses.

Week Thirty-two

Lanugo begns to fall off.

Week Thirty-three

Bones begin to harden.

Week Thirty-four

Vernix thickens before shedding in a few weeks.

Week Thirty-five

Baby may begin to drop into your pelvis, engaging for delivery. Most of baby's growth now is fat.

Week Thirty-six

Vernix disappears.

Week Thirty-seven

Immune system begins to prime. May be considered full-term.

Week Thirty-eight

Lungs continue to get stronger.

Week Thirty-nine and beyond...

Continues to grow!