5 weeks pregnant: the size of a sesame seed
The neural tube, which becomes the brain and spinal cord, starts forming. The heart begins to develop.
Reviewed against ACOG, NHS and WHO guidance · Updated November 2026
Typical size
About 2 mm
13% of the way to your due date
Your baby this week
The neural tube, which becomes the brain and spinal cord, starts forming. The heart begins to develop.
Your body this week
Tender breasts, tiredness and needing to pee more often are common.
Tip for week 5
Ask your provider about any medicines you take regularly before stopping or continuing them.
Carry this guide in your pocket
Mamivaa is a free pregnancy app with a week-by-week tracker, vitamin and water reminders, a food scanner and a baby checklist.
Start freeThis guide offers general information and does not replace advice from your doctor or midwife. If something feels wrong, contact your provider or emergency services.