Trimester 1
Week 4
About the size of
a poppy seed
~0.1 cm
Averages only: a scan is the only way to know your baby’s size.
Your baby this week
The embryo has just implanted in the uterine lining and is dividing rapidly. The three layers that will become the nervous system, organs and skin are forming.
What you may feel
Most people have just missed a period or seen a positive test. Tender breasts, tiredness and mild cramping are common, and easy to mistake for premenstrual symptoms.
Don’t miss
Book your first antenatal appointment: most providers want to see you between weeks 8 and 10.
Timing varies by province and by care team: ask yours.
This week, try
Start a daily folic acid supplement (400 µg) if you have not already: it protects neural tube development, which is happening right now.
Weeks are counted from the first day of your last period, as your care team counts them. Written by The Childhood Journal’s team from standard prenatal references. Not yet reviewed by a clinician: our scientific board is being formed. General information, never an assessment of your pregnancy.