Fetal Development
How the Baby Grows: Week by Week
A fetus is a developing human being with its own separate, distinct set of DNA that manages its own development. Nourishment is the only thing it will need to grow – from conception until the end of its natural life.1, 2
- Week 1: Last Menstrual Period
- Week 2: Conception
- Week 3: Baby attaches to the uterus
- Week 4: Nerves, brain and spinal cord begin to develop
- Week 5: Baby's heart begins to beat
- Week 6: Eyes, arms, legs, lungs, and stomach begin to form
- Week 7: Hands and feet are forming
- Week 8: Upper lip, teeth, fingers, and ears begin to form
- Week 9: Toes and genitals are forming
- Week 10: Baby has permanent fingerprints
- Week 11: Baby starts to produce urine
- Week 12: Fingernails are forming
- Week 13: Baby flexes and kicks
- Week 14: Hormones gear up
- Week 15: Skin begins to form
- Week 16: Facial expressions are possible
- Week 17: Fat accumulates
- Week 18: Baby begins to hear
- Week 19: Lanugo covers baby's sking
- Week 20: The halfway point
- Week 21: Nourishment evolves
- Week 22: Taste buds develop
- Week 23: Lungs prepare for life outside the womb
- Week 24: Sense of balance develops
- Week 25: Exploration continues
- Week 26: Eyes remain closed
- Week 27: Second trimester ends
- Week 28: Baby's eyes open
- Week 29: Movement is more forceful
- Week 30: Baby packs on pounds
- Week 31: Reproductive development continues
- Week 32: Downy hair falls off
- Week 33: Baby detects light
- Week 34: Protective coating gets thicker
- Week 35: Rapid growth continues
- Week 36: Baby can suck
- Week 37: Baby is full-term
- Week 38: Organ function continues to improve
- Week 39: Placenta provides antibodies
- Week 40: Your due date arrives
Medically Reviewed By:
Tessa, NP
Staff Nurse Practitioner, Baton Rouge
1 Videos: The Endowment for Human Development (2011). Retrieved April 2022 from https://www.ehd.org/movies
2 Week by Week info: Mayo Clinic (2020). Pregnancy week by week. Retrieved June 2021 from Pregnancy week by week Healthy pregnancy – Mayo Clinic
