3 of 40 weeks
Baby size this week
As lovely as a sesame seed
Measurements are averages — every baby grows at their own pace.
Length 0.2 cm 0.1 in
Weight 0.1 g 0.00 oz
Your baby this week
- Fertilization typically happens near the end of this week
- The fertilized egg becomes a single cell called a zygote
- It begins dividing as it travels to the uterus
- Implantation will begin in the coming days
Your body this week
Light spotting
Mild cramping
Breast tenderness
This week's to-do
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How we measure week 3
Pregnancy weeks are counted from the first day of your last menstrual period, following standard ACOG and NHS guidance. Sizes are crown-rump length in early weeks and head-to-heel from around week 20. Your care team may adjust dates after an ultrasound.
BumpCount offers general information and does not replace advice from your doctor or midwife.