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Transcript of Associations between gestational weight gain and child BMI at age 5 Author 1 Author 2 December 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: 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
US Prevalence of Overweight Among Children Ages 2-5
0%
2%
4%
6%
8%
10%
12%
14%
16%
1971-74
1976-1980
1988-94
1999-2000
2001-02
2003-04
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 [0.08-0.19])
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 BMI Paternal 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:
<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
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)
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 (>10th percentile, 10th-90th, <90th 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 (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.
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)
RESULTS:Final model
Significant interactions: black race x gestational weight gain low pre-pregnancy BMI x gestational weight gain
Characteristic Child BMI z-score β
95% CI
white low bmi 0.18 (0.05, 0.32)
white normal bmi 0.06 (-0.01, 0.13)
white high bmi 0.12 (-0.05, 0.30)
white very high bmi 0.03 (-0.16, 0.22)
black low bmi 0.28 (0.12, 0.43)
black normal bmi 0.16 (0.05, 0.26)
black high bmi 0.22 (0.04, 0.40)
black very high bmi 0.12 (-0.07, 0.31)
other low bmi 0.24 ( 0.03, 0.46)
other normal bmi 0.12 (-0.07, 0.31)
other high bmi 0.18 (-0.07, 0.43)
other very high bmi 0.09 (-0.17, 0.35)
RESULTS:Coefficient estimate (slope) on gestational weight gain by race & maternal BMI*
Maternal BMI Category
BMI
Low <19.8
Normal 19.8 – 26.0
High 26.1 – 29.0
Very High >29.0
Black women
-0.35
-0.25
-0.15
-0.05
0.05
0.15
0.25
0.35
0.45
0.55
low normal high very high
Pre-pregnancy BMI category
change in
child
BM
I z-s
core
per
5 k
g w
eig
ht gain
White women
-0.35
-0.25
-0.15
-0.05
0.05
0.15
0.25
0.35
0.45
0.55
low normal high very high
Pre-pregnancy BMI category
change in
child
BM
I z-s
core
per
5 k
g w
eig
ht gain
Women of other ethnicity
-0.35
-0.25
-0.15
-0.05
0.05
0.15
0.25
0.35
0.45
0.55
low normal high very high
Pre-pregnancy BMI category
change in
child
BM
I z-s
core
per
5 k
g w
eig
ht gain
I
*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*
Black women-2.8
-2.3
-1.8
-1.3
-0.8
-0.3 0 5 10 15
Gestational weight gain (kg)
ch
ild
BM
I z-
sco
re
Low BMI
Normal BMI
High BMI
Very High BMI
White women-2.8
-2.3
-1.8
-1.3
-0.8
-0.3 0 5 10 15
Gestational weight gain (kg)
ch
ild
BM
I z-
sco
re Low BMI
Normal BMI
High BMI
Very High BMI
Maternal BMI Category
BMI
Low <19.8
Normal 19.8 – 26.0
High 26.1 – 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.
Women of other ethnicity-2.8
-2.3
-1.8
-1.3
-0.8
-0.3 0 5 10 15
Gestational weight gain (kg)
ch
ild
BM
I z-
sco
re
Low BMI
Normal BMI
High BMI
Very High
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 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
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 interactionCharacteristic Child BMI z-
score β95% CI
Gestational weight gain (5kg) (GWG) 0.06 -0.01 – 0.13
Smoking Status
Smoked during preg (vs. never smoked) 0.09 -0.00 – 0.18
Quit before pregnancy(vs. never smoked) -0.08 -0.19 – 0.03
Race: Black (vs. White) -0.29 -0.58 – -0.01
Other (vs. White) -0.06 -0.51 – 0.40
Total household income below the Median (vs. Above) -0.06 -0.14 – 0.03
Single, Separated, Divorced, Widowed (vs. Married) -0.12 -0.44 – 0.21
Days gestation -0.002 -0.005 – 0.001
Female (vs. Male) -0.03 -0.11 – 0.05
Paternal BMI (kg/m2) ≥25 (vs. <25) 0.06 0.05 – 0.08
Maternal prepregnancy BMI (kg/m2)
Low <19.8 (vs. 19.8-26.0) -0.60 -0.95 – -0.26
High 26.1-29.0 (vs. 19.8-26.0) 0.09 -0.34 – 0.52
Very high >29.0 (vs. 19.8-26.0) 0.50 0.06 – 0.94
GWG x low BMI 0.12 -0.02 – 0.26
GWG x high BMI 0.06 -0.12 – 0.24
GWG x very high BMI -0.03 -0.22 – 0.16
GWG x Black race 0.09 -0.02 – 0.21
GWG x Other race 0.06 -0.14 – 0.25