Evid Based Nurs 1:122 doi:10.1136/ebn.1.4.122
  • Causation

Pregnancy within 8 months of a previous birth was associated with an increased rate of preterm birth

 Question Are short interpregnancy intervals, defined as ≤8 months, associated with an increased risk of low birth weight or preterm delivery?


Cohort study.




10 187 women who had 2 births between 1980 and 1992. Exclusion criteria were multiple births, stillbirths, and incomplete records for birth weight and gestational age of the child.

Assessment of risk factors

Interpregnancy interval was defined as ≤4, 4.01–8.00, 8.01–12.00, 12.01–24.00, 24.01–36.00, and >36 months and calculated as the difference between the birthdate of the first child and estimated date of conception of the second child in the study pair. The interval 24.01–36.00 months was taken as the reference standard (odds ratio [OR] 1.0). Other risk factors were age of mother at second study birth, parity at first study birth, social status (low, medium, and high) at …

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