Baby development at week 3
The blastocyst may attach to the uterine lining. Tiny hormonal shifts start, but they are often too early for clear symptoms or a reliable test.
Average size estimates for week 3 are about still microscopic and too early to weigh meaningfully — roughly poppy seed stage. Your ultrasound report and clinician’s dating override any website average.
What you might feel
Mild cramping or spotting can happen with implantation — or with a regular cycle. Do not assume either way without a test and clinical context.
You are in the first trimester. Two pregnancies at the same week can feel completely different — treat these notes as orientation, not a checklist you must match.
What to track this week
- Symptoms, mood, sleep, and energy in your daily log
- Water intake toward a simple daily goal
- Appointment dates and questions for your care provider
A calm next step in Preglo
When you are ready, Preglo can store the date you first suspected pregnancy alongside your eventual due date.
Also useful: due date calculator · all weeks · Preglo features
Nearby weeks: Week 1 · Week 2 · Week 4 · Week 5
Educational averages only — not medical advice. Contact your clinician for symptoms that worry you, bleeding, severe pain, or reduced movements.