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What week are you most likely to go into labor?

Last updated on June 4, 2026

Most babies are not born on their due date. By 38 weeks, only about half of women will have given birth; most first-time mothers without induction will deliver between 39 and 41 weeks. The peak probability of spontaneous labor occurs between weeks 39 and 40, with about 26% of births happening in the 40th week.

Evidence Summary

  • Data source: Large observational cohort studies of spontaneous labor onset across gestational weeks

  • Key finding: Week 39–40 has the highest probability of labor; week 41 accounts for a meaningful share, especially for first-time mothers

  • Key finding: Only ~10% of women deliver before 37 weeks (preterm)

  • Caveat: These figures apply to pregnancies without induction; induction significantly shifts timing distributions

  • Caveat: First pregnancies tend to run later than subsequent pregnancies on average

Confidence: High confidence — based on large observational cohort data; timing varies significantly by individual and whether labor is induced.

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