Birth weight and blood pressure: ‘J’ shape or linear shape? Findings from a cross-sectional study in Hong Kong Chinese women

OBJECTIVES To investigate the association between birth weight and blood pressure (BP) and to determine the effect of body size change from birth to adulthood on BP. DESIGN A cross-sectional design to collect retrospective data. PARTICIPANTS 1253 female nurses aged 35-65 years in Hong Kong. MAIN OUTCOME MEASURES Birth weight, height, weight, BP, waist circumference, demographics and lifestyle factors were collected by a self-administered questionnaire through mail survey. These self-reported variables have been validated in a pilot study. The conditional relative weight (CRW), which was calculated as a residual of current weight regressed on birth weight, was used to express higher or lower relative weight gain from birth to adulthood. RESULTS No significant linear association between overall range of birth weight and BP was found. The curve estimation showed a significant quadratic curvilinear association ('J' shape). In the piecewise-linear analysis, a significant inverse association between birth weight z-scores and BP was observed in the birth weight ≤3.1 kg group (systolic BP (SBP): coefficient B=-1.73, 95% CI -3.17 to -0.30; diastolic BP (DBP): B=-1.12, 95% CI -2.19 to -0.06). A positive but non-significant association occurred in the birth weight >3.1 kg group. Participants who belonged to the lowest 10% birth weight category but at the current top 10% BMI group had higher BP than participants in other BMI groups. The CRW z-score was positively associated with BP (coefficient B: 4.18 for SBP and 2.87 for DBP). CONCLUSIONS Unlike most previous studies, we found a 'J' shape association rather than a linear association between birth weight and BP. Women with large percentile crossing of body size from birth to adulthood were more likely to have elevated BP. A higher weight gain from birth to adulthood than expected led to higher BP.