Figure 2. Relative Risk for Associations Between Preterm Birth and Upward or Downward Mobility.

A, Associations between preterm birth and upward mobility, stratified by family income quintiles at birth, in the matched cohort. B, Associations between preterm birth and downward mobility, stratified by family income quintiles at birth, in the matched cohort. Individuals were categorized into 3 groups according to whether they moved up (upward mobility), down (downward mobility), or stayed in the same quintile (Q) relative to their parent (reference category). Preterm birth was categorized as a binary variable (24-36 weeks vs 37-41 weeks) and a multicategory variable (34-36, 32-33, 28-31, and 24-27 weeks, relative to 37-41 weeks [reference category]).