General information only. This Parent Resource summarizes WHO public-health information about preterm birth and does not assess an individual pregnancy or baby.

What does preterm birth mean?

WHO defines a preterm baby as a baby born alive before 37 completed weeks of pregnancy.

How does WHO group preterm birth by gestational age?

WHO describes three gestational-age groups: extremely preterm at less than 28 weeks, very preterm from 28 to less than 32 weeks, and moderate to late preterm from 32 to 37 weeks.

How common is preterm birth globally?

WHO estimated that 13.4 million babies were born preterm in 2020. WHO also reports substantial differences between countries in both preterm-birth rates and survival.

Why can preterm birth happen?

WHO states that many preterm births happen spontaneously, while others occur because pregnancy complications create a medical reason for an earlier birth. Multiple pregnancy, infections and chronic conditions are among associated factors, but in many cases no single cause is identified.

Why do outcomes differ between settings?

WHO describes large global inequalities in survival and disability after preterm birth, reflecting differences in access to appropriate maternal and newborn care.

A gestational-age category is not an individual prognosis. Outcomes depend on many clinical and health-system factors that cannot be determined from a general information page.

References

  1. World Health Organization. Preterm birth, 10 May 2023.