title: Birth weight and blood pressure: 'J' shape or linear shape? Findings from a cross-sectional study in Hong Kong Chinese women.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  A cross-sectional design to collect retrospective data.
  
  
  METHODS
  1253 female nurses aged 35-65 years in Hong Kong.
  
  
  METHODS
  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.
authors.affiliation: Department of Sports Science and Physical Education, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Yao Jie
authors.identifier: http://orcid.org/0000-0001-9289-4985
authors.initials: YJ
authors.lastname: Xie
authors.affiliation: Division of Epidemiology, The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Ho
authors.affiliation: Department of Medicine & Therapeutics, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Zhao-Min
authors.initials: ZM
authors.lastname: Liu
authors.affiliation: Department of Sports Science and Physical Education, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Stanley Sai-Chuen
authors.initials: SS
authors.lastname: Hui
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D001724:Birth Weight; D001794:Blood Pressure; D003430:Cross-Sectional Studies; D005260:Female; D006723:Hong Kong; D006801:Humans; D008875:Middle Aged; D012189:Retrospective Studies
keywords: Birth weight; Blood pressure; Body mass index; Chinese women; Fetal programming