Crudely, there was a slight suggestion of a U- or J-shaped relationship between BW and BP (Figure 2). Compared with those with BW 3.00–3.49 kg, the difference in adjusted mean systolic BP was +0.30 mmHg, 95% CI (−1.87, +2.47), −0.07 mmHg, 95% CI (−1.50, +1.35) and +0.78 mmHg, 95% CI (−0.56, +2.11) among those with BW <2.5 kg, 2.5–2.99 kg and ≥3.5 kg, respectively (Supplementary Table 3, available as Supplementary data at IJE online). However, confidence intervals were wide and treating BW as a categorical variable in the regression model did not improve the fit of the model to the data compared with a linear model (P-values for departure from linearity 0.253 and 0.404 for systolic and diastolic BP, respectively). Regardless of whether or not BW was modelled as categorical or linear, there was no evidence for association between BW and BP; for example, linear model regression coefficients were β = 0.14, 95% CI (-1.00, 1.27) for systolic and β = 0.43, 95% CI (-0.57, 1.43) for diastolic BP (Table 1).