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Associations between gestational weight gain and child BMI at age 5

Associations between gestational weight gain and child BMI at age 5. Author 1 Author 2 December 5, 2007 PH 251. BACKGROUND: Childhood overweight. Increased prevalence of childhood overweight 13.9% among 2-5 year olds (2003) Risk factor for:

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Associations between gestational weight gain and child BMI at age 5

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  1. Associations between gestational weight gain and child BMI at age 5 Author 1 Author 2 December 5, 2007 PH 251

  2. BACKGROUND:Childhood overweight • Increased prevalence of childhood overweight • 13.9% among 2-5 year olds (2003) • Risk factor for: • Coronary heart disease, hypertension, type 2 diabetes, high cholesterol, bone and joint problems, sleep apnea, psychosocial problems, adult overweight or obesity • Importance of identifying early and modifiable risk factors Source: CDC, from NHANES data

  3. BACKGROUND:Gestational weight gain • IOM guidelines from 1990 • Increase in women gaining both above and below guidelines • IOM reconsidering guidelines in 2008 “This is a topic of great interest.” – Christine Stencel, IOM spokeswoman

  4. BACKGROUND:Summary of literature • 4 of 8 studies did not find an association (but used pregnancy weight gain as covariate not as main effect) • 3 studies that found an association were published only as abstracts • Oken et al (2007) found positive association between gestational weight gain and higher child BMI z-score (0.13 units per 5 kg [0.08-0.19])

  5. Race/ethnicity Maternal BMI Paternal BMI Gestational weight gain (total kg or IOM categories) Birthweight for gestational age Child BMI z-score (age 4 to 6) Smoking during pregnancy Infant sex Sociodemographic characteristics (income, education, marital status) BACKGROUND:Is birthweight on the causal pathway? *birthweight for gestational age = a measure of fetal growth that adjusts for length of gestation

  6. OBJECTIVE: • Assess association between gestational weight gain (total kg) and child BMI z-score at age 5

  7. METHODS: Study population • N=3537 • First, live, singleton births without severe congenital anomalies • Maternal exclusions: • <15 or >44 yrs • missing values of height or weight • implausible values of • gestational length (<154 or >308 days) • gestational weight gain (trimmed top & bottom 1% of data) • Child exclusions: • no measured value of height or weight between ages 4 to 6 • implausible values of • birthweight for gestational age (omitted using Alexander, 1996 critera) • BMI (trimmed top & bottom 1% of data) • Final analysis only included pairs with information on: paternal BMI, race, smoking status, income, marital status

  8. METHODS:Measurement of child BMI • Child height & weight from 5 year exam or from routine visit closest to 5th birthday • Used to calculate Body Mass Index (BMI) Z-score • BMI = weight/height2 • Z-score • Standardizes child’s BMI by sex and age • CDC 2000 reference population (U.S. data from 1971-1994)

  9. METHODS:Measuring gestational weight gain • = Mother’s last weight before delivery – pre-pregnancy weight • Last weight before delivery measured within 28 days of delivery • Pre-pregnancy weight self-reported or measured before 12 weeks of pregnancy (correlation = 0.93)

  10. METHODS: Key covariates assessed • Child: • Sex • Birthweight for gestational age(>10th percentile, 10th-90th, <90th percentile) • Maternal: • Age (15-24, 25-34, 35-44) • Race/ethnicity (white, black, other) • Education (≤ some high school, >high school vs high school) • Income (below vs above median) • Marital status (not married vs married) • Parity (parous vs nulliparous) • Maternal BMI (low, normal, high, very high) • Paternal BMI (high vs normal) • Smoking (current, quit before preg, never)

  11. METHODS:Model Selection • Multivariate linear regression: • child BMI z-score = gestational weight gain (5kg) + covariates • Covariate selection based on Oken et al, 2007 and a priori hypotheses: • used restricted vs full F-test to determine best fit model • final model included: race, income, marital status, smoking, gestation length, child sex, maternal BMI, paternal BMI, birthweight for gestational age • chose model without birthweight because of hypothesis that it is on causal pathway • Assessed interaction by: • race, maternal BMI, paternal BMI, smoking, child sex

  12. RESULTS: Study population characteristics • 67% white, 24% black, 9% other • BMI: • 70% normal (19.8-26.0) • 20% low (<19.8) • 6% high (26.0-29.0), 4% very high (>29.0) • 37% paternal overweight • 33% smoked during pregnancy • Majority income above median and high school education or more.

  13. RESULTS:Main exposure and outcome • Mean gestational weight gain = 11.5 kg • Mean child BMI z-score = -0.26 (Interpret as standard deviations away from mean BMI for sex, age based on 2000 CDC reference)

  14. RESULTS:Final model • Significant interactions: • black race x gestational weight gain • low pre-pregnancy BMI x gestational weight gain

  15. RESULTS:Coefficient estimate (slope) on gestational weight gain by race & maternal BMI* *From multivariate linear regression adjusted for race, income, marital status, maternal BMI, paternal BMI, smoking, and child sex

  16. RESULTS:Change in Child BMI Z-Score per Kilogram Gestational Weight Gain By Race & Maternal BMI* *Adjusted predicted value for female children of married, non-smoking mothers, and non-overweight fathers (BMI<25) with income above the median.

  17. DISCUSSION:Comparison to previous studies • Association of gestational weight gain and child BMI z-score at age 5 only significant among women of black race or low pre-pregnancy BMI • Multivariate models support results of Oken et al but finding of interaction is novel • Oken et al assessed interaction for high BMI vs normal only • Study supports positive association found in previous research • Shack-Nielsen et al did not find interaction by pre-pregnancy BMI • Sharma et al also found stronger effect among women of low BMI • Seidman did not assess interaction

  18. DISCUSSION:Limitations and strengths • Limitations: • no measure of glucose tolerance or breastfeeding • low R2 for final model • generalizability • What our study adds: • cohort was born before current obesity epidemic • examine gestational weight gain at a time when recommendations were more restrictive • no other studies examined interaction by race • most studies adjust for birthweight for gestational age

  19. DISCUSSION:Possible mechanisms • Genetics • Environmental/lifestyle factors shared by mother and child • Biological effect of weight gain on child adiposity • Changes in adipocyte cell size and number, proportions of fat and lean body mass • Central nervous system appetite control • Pancreatic structure and function

  20. IMPLICATIONS: • Recommendations for gestational weight gain should account for differences by race/ethnicity and pre-pregnancy BMI • Future research: • Examination of IOM categories of gestational weight gain • Other measures of adiposity • Adiposity throughout life course • More evidence from current obesity epidemic

  21. Acknowledgements: Brenda Eskenazi, PhD David Lein, MS Barbara Abrams, DrPH, RD Maureen Lahiff, PhD Our 251 classmates!

  22. RESULTS: Multivariate model with interaction

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