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