Baby development at week 1
Clinically, week 1 is often the week of your last menstrual period. Conception has not happened yet for most people; the calendar is simply starting so clinicians can estimate a due date later.
Average size estimates for week 1 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
You may feel like your usual cycle. There is nothing pregnancy-specific to track yet unless you are actively trying to conceive and logging periods.
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
Log your period start date in Preglo so week math stays consistent later.
Also useful: due date calculator · all weeks · Preglo features
Educational averages only — not medical advice. Contact your clinician for symptoms that worry you, bleeding, severe pain, or reduced movements.