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First trimester

Week 4 of Pregnancy

🌱Your baby this week

• The tiny embryo has implanted in the uterine lining and is officially setting up home.
• The hormone hCG rises quickly — it is exactly what a home pregnancy test detects.
• The amniotic sac and the earliest placenta structures begin forming.

🫧What you may be feeling

• Missed period
• Light spotting for some (implantation)
• Tender breasts and fatigue

🤍Gentle tips for this week

• Take a pregnancy test and, if positive, call a provider to schedule your first prenatal visit.
• Start a simple note of dates — your last period date sets your due date.

Common question for week 4

How big is the baby at 4 weeks?

About the size of a poppy seed — roughly a millimeter. Despite the tiny size, the hormone signals establishing the pregnancy are already strong enough for a positive test.

Every pregnancy is different. Sizes are averages, symptoms vary widely, and none of this replaces the guidance of your own provider.