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: 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

BACKGROUND: Gestational weight gain IOM guidelines from 1990 Increase in women gaining both above and below guidelines IOM reconsidering guidelines in 2008 Pre-pregnancy Weight for Height BMI Recommended Total Gain kgs Low (BMI <19.8)12.5 – 18 Normal (BMI 19.8 – 26.0)11.5 – 16 Overweight (BMI 26.0 – 29.0)7 – 11.5 Obese (BMI >29.0)>6.0 “This is a topic of great interest.” – Christine Stencel, IOM spokeswoman

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 [ ])

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

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

METHODS: Study population N=3537 First, live, singleton births without severe congenital anomalies Maternal exclusions: 44 yrs missing values of height or weight implausible values of gestational length ( 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

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/height 2 Z-score Standardizes child’s BMI by sex and age CDC 2000 reference population (U.S. data from )

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)

METHODS: Key covariates assessed 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) Child: Sex Birthweight for gestational age (>10 th percentile, 10 th -90 th, <90 th percentile)

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

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

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

RESULTS: Final model Significant interactions: black race x gestational weight gain low pre-pregnancy BMI x gestational weight gain CharacteristicChild BMI z-score β 95% CI white low bmi0.18(0.05, 0.32) white normal bmi0.06(-0.01, 0.13) white high bmi0.12(-0.05, 0.30) white very high bmi0.03(-0.16, 0.22) black low bmi0.28(0.12, 0.43) black normal bmi0.16(0.05, 0.26) black high bmi0.22(0.04, 0.40) black very high bmi0.12(-0.07, 0.31) other low bmi0.24( 0.03, 0.46) other normal bmi0.12(-0.07, 0.31) other high bmi0.18(-0.07, 0.43) other very high bmi0.09(-0.17, 0.35)

RESULTS: Coefficient estimate (slope) on gestational weight gain by race & maternal BMI* Maternal BMI Category BMI Low<19.8 Normal19.8 – 26.0 High26.1 – 29.0 Very High>29.0 *From multivariate linear regression adjusted for race, income, marital status, maternal BMI, paternal BMI, smoking, and child sex

RESULTS: Change in Child BMI Z-Score per Kilogram Gestational Weight Gain By Race & Maternal BMI* Maternal BMI Category BMI Low<19.8 Normal19.8 – 26.0 High26.1 – 29.0 Very High>29.0 *Adjusted predicted value for female children of married, non-smoking mothers, and non-overweight fathers (BMI<25) with income above the median.

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

DISCUSSION: Limitations and strengths Limitations: no measure of glucose tolerance or breastfeeding low R 2 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

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

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

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

RESULTS: Multivariate model with interaction CharacteristicChild BMI z- score β 95% CI Gestational weight gain (5kg) (GWG) – 0.13 Smoking Status Smoked during preg (vs. never smoked) – 0.18 Quit before pregnancy (vs. never smoked) – 0.03 Race: Black (vs. White) – Other (vs. White) – 0.40 Total household income below the Median (vs. Above) – 0.03 Single, Separated, Divorced, Widowed (vs. Married) – 0.21 Days gestation – Female (vs. Male) – 0.05 Paternal BMI (kg/m 2 ) ≥25 (vs. <25) – 0.08 Maternal prepregnancy BMI (kg/m 2 ) Low <19.8 (vs ) – High (vs ) – 0.52 Very high >29.0 (vs ) – 0.94 GWG x low BMI – 0.26 GWG x high BMI – 0.24 GWG x very high BMI – 0.16 GWG x Black race – 0.21 GWG x Other race – 0.25