Pregnancy · week by week
How your baby grows.
Week-by-week fetal development and the changes in your own body, based on current clinical evidence and peer-reviewed embryology research. Pick a week, or step through from the very beginning.
First trimester
Week 1: Fertilisation
A single cell (~0.1 mm)
Approximate size
< 1 g
Approximate weight
Baby’s development
- After fertilisation, the single-celled zygote begins dividing as it travels down the fallopian tube.
- It already carries the full set of genetic material that shapes your baby.
Your body
- You likely won't feel any different yet.
- Your body starts producing the hormones that support a pregnancy.
Week 1
Based on current clinical evidence and peer-reviewed embryology research. Every pregnancy is unique. Consult your healthcare provider for personalised advice.
herjourney.com.au · Health education, not medical advice
Evidence: peer-reviewed embryology research, ACOG definitions · © Her Journey 2026