First Trimester: Weeks 1-12

Content reviewed against published ACOG, AAP guidelines

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The first trimester spans weeks 1 through 12 and is a critical period of early development.

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources

Bottom line

The first trimester brings many changes. Talk to your healthcare provider about any concerns.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.