Associations of Birth Order with Early Adolescent Growth, Pubertal Onset, Blood Pressure and Size: Evidence from Hong Kong's "Children of 1997" Birth Cohort.
Man Ki Kwok
Gabriel M Leung
C Mary Schooling
- Publisher: Public Library of Science (PLoS)
(issn: 1932-6203, eissn: 1932-6203)
Vascular Medicine | Research Article | Anatomy | Research Design | Body Weight | Population Groupings | Hair | People and Places | Children | Endocrine Physiology | Puberty | Blood Pressure | Birth Weight | Biology and Life Sciences | Infants | Research and Analysis Methods | Physiology | Birth | Maternal Health | Integumentary System | Medicine | Families | Age Groups | Q | R | Physiological Parameters | Women's Health | Obstetrics and Gynecology | Science | Cohort Studies | Medicine and Health Sciences | Endocrinology
Background Birth order has been proposed as a cardiovascular risk factor, because the lower birth weight and greater infant weight gain typical of firstborns could programme metabolism detrimentally. Methods We examined the associations of birth order (firstborn or laterborn) with birth weight-for-gestational age, length/height and body mass index (BMI) z-scores during infancy, childhood, and puberty using generalized estimating equations, with age at pubertal onset using interval-censored regression and with age-, sex- and height-standardized blood pressure, height and BMI z-scores at 13 years using linear regression in a population-representative Chinese birth cohort: “Children of 1997” (n = 8,327). Results Compared with laterborns, firstborns had lower birth weight-for-gestational age (mean difference = -0.18 z-score, 95% confidence interval (CI) -0.23, -0.14), lower infant BMI (-0.09 z-score, 95% CI -0.14, -0.04), greater childhood height (0.10 z-score, 95% CI 0.05, 0.14) and BMI (0.08 z-score, 95% CI 0.03, 0.14), but not greater pubertal BMI (0.05 z-score, 95% CI -0.02, 0.11), adjusted for sex, parental age, birthplace, education and income. Firstborns had earlier onset of pubic hair (time ratio = 0.988, 95% CI 0.980, 0.996), but not breast or genitalia, development. Firstborns had greater BMI (0.07 z-score, 95% CI 0.002, 0.15), but not height (0.05 z-score, 95% CI -0.01, 0.11), at 13 years, but similar blood pressure. Conclusions Differences by birth order continue into early adolescence with firstborns being heavier with earlier pubic hair development, which could indicate long-term cardiovascular risk.
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Related Research Results
Adjusted<sup>a</sup> association of birth order with birth weight-for-gestational age z-score for growth during fetal phase, height and body mass index (BMI) z-scores during infancy, childhood and pubertal phases, age at onset of breast or genitalia or pubic hair development (Tanner stage II) and blood pressure, height and BMI z-scores at 13 years in the Hong Kong’s “Children of 1997” birth cohort, Hong Kong, China, 1997–2010.
Baseline characteristics by birth order for 8,260 adolescents from Hong Kong’s “Children of 1997” birth cohort, Hong Kong, China, 1997–2010.
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