Fig. 3

Unadjusted and adjusted Relative Risk from interaction models for the association between post-birth interpregnancy intervals and adverse birth outcomes in twin pregnancies. The prevalence rate of adverse birth outcomes: (a) preterm birth; (b) early preterm birth; (c) at least one twin being classified as low birth weight; and (d) at least one twin being classified as small for gestational age, is overlayed with the relative risk of adverse birth outcomes for each outcome. Adjusted model based on pooled analysis from 20 imputed datasets controlling for: parity, birth year category, maternal ethnicity, maternal marital status at time of birth, maternal age at time of birth, maternal occupational status scale at time of birth, previous maternal history for each respective outcome variable, and Index of Relative Socioeconomic Disadvantage category. All relative risk data is presented with 95% confidence intervals: modified Poisson Regression