Background and objective: A continued controversy exists whether the assessment of the influence of low birth weight on adult blood pressure necessitates adjustment for adult weight in the analysis on the fetal origins of adult diseases hypothesis. Here we first explain the difficulty in understanding an adjusted multivariate regression model, and then propose another way of writing the regression model to make the interpretation of the separate influence of birth weight and changes in weight later in life more straightforward.
Study design and setting: We used a multivariate regression model containing birth weight (standard deviation score; SDS), and residual adult weight (SDS) to explore the effect on blood pressure (or any other outcome) separately. Residual adult weight was calculated as the difference between actual adult weight and the expected adult weight (SDS) given on a certain birth weight (SDS).
Results: The coefficients of birth weight and residual adult weight show directly the effect on the analyzed outcome variable.
Conclusions: We prefer to use this regression model with unexplained residuals when the adjusted variable is in the causal pathway in the analyses of data referring to the fetal origins of adult diseases hypothesis.