Fetal Development

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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 skin
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

Cindy P, BSN, RN

Medically Reviewed By:


1 Videos: The Endowment for Human Development (2011). Retrieved June 2021 from https://www.ehd.org/get-free-videos.php

2 Week by Week info: Mayo Clinic (2020). Pregnancy week by week.  Retrieved June 2021 from Pregnancy week by week Healthy pregnancy – Mayo Clinic

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