In this study half of the children were male (50%), and 30% were nonwhite. At birth, their mean birthweight was 3.53 kg (SD, 0.51 kg), with a mean gestational age of 39.7 weeks (SD, 1.4 weeks). At 6 months, the infants’ mean WFL z score was 0.68 (SD, 0.94; range, −2.96 to 3.24). Mean WFL z score at birth was 0.47 (SD, 0.76); mean length-for-age z score was 0.02 (SD, 0.83) at birth and −0.04 (SD, 0.86) at 6 months of age. The mean change in WFL z score from birth to 6 months of age was 0.21 (SD, 1.08). At 6 months, 52% of children were being fed breast milk. Most mothers (74%) had at least a college education, and 67% lived in households with an annual income of more than $70,000; 15% of mothers and 15% of fathers had a previous history of physician-diagnosed asthma. By age 3 years, 30% of children had any wheezing, 14% of children had recurrent wheezing, and 13% had current asthma.
In bivariate analyses children with higher 6-month WFL z scores were more likely to have higher birthweights and have mothers with higher prepregnancy BMIs and were less likely to be breast-fed (). The home environment of children with higher 6-month WFL z scores was characterized by somewhat more passive smoke exposure, but no difference in exposure to siblings less than age 12 years, pets, or other common allergens.
Characteristics of 932 infants in Project Viva according to quartiles of the infants’ 6-month WFL z scores
In age- and sex-adjusted multivariable models we observed a direct association between 6-month WFL z score and risk of any wheezing and recurrent wheezing at age 3 years (). The direct association between WFL z score at 6 months and recurrent wheeze was robust to controlling for a variety of potential confounders (). Compared with children in the lowest quartile of WFL z scores at 6 months (median within quartile, −0.39), those in the highest quartile (median, 1.78) had higher risk of recurrent wheeze at age 3 years (OR, 2.25; 95% CI, 1.10–4.60).
Associations of quartile of 6-month WFL z scores with risk of clinical outcomes during the first 3 years of life
shows risk of any wheezing, recurrent wheezing, and current asthma with infants’ WFL z scores at 6 months, expressed as a 1-unit increment rather than in quartiles and stratified by sex. We found that each 1-unit increment in 6-month WFL z score was associated with greater odds of having had any wheezing (OR, 1.23; 95% CI, 1.03–1.48) or recurrent wheezing by 3 years of age (OR, 1.46; 95% CI, 1.11–1.91). We found a weaker association of 6-month WFL z score with current asthma (OR, 1.22; 95% CI, 0.94–1.59). In fully adjusted multivariable models we did not observe substantial differences in risks between boys and girls (). Furthermore, the association between 6-month WFL z score and risk of wheezing did not vary by birthweight, and adjustment for birthweight did not attenuate the observed estimates. For example, in multivariable models not adjusted for birthweight, the odds of recurrent wheeze was 1.44 (95% CI, 1.10–1.88) for each 1-unit increment in 6-month WFL z score. After adjustment for birthweight, the odds of recurrent wheeze was 1.46 (95% CI, 1.11–1.91). Independently, birthweight was not associated with any of the outcomes. For example, the odds of recurrent wheeze was 0.81 (95% CI, 0.50–1.32) for each 1-kg increment in birthweight.
Associations of 6-month WFL z score with risk of clinical outcomes during the first 3 years of life stratified by sex
Subgroup analyses of change in WFL z score in the first 6 months of life (ie, WFL z score at 6 months adjusted for WFL z score at birth) revealed very similar results to those examining attained adiposity. Each 1-unit increment in WFL z score at 6 months (adjusted for WFL z score at birth) was associated with increased odds of any wheezing (OR, 1.17; 95% CI, 0.91–1.49) and recurrent wheezing (OR, 1.39; 95% CI, 0.95–2.04). However, with a relatively low sample size (n = 569), the CIs were wider than those in the main analyses. Independently, change in length-for-age in the first 6 months of life was not associated with any of the outcomes (data not shown).
Among the 494 participants with available serum IgE data, 196 (40%) had plasma manifestations of atopy. In multivariable logistic regression analyses 6-month WFL z
score was not associated with atopy alone (OR, 1.04; 95% CI, 0.83–1.29). In addition, higher adiposity in infancy was not associated with the atopic form of recurrent wheezing (see Table E1
in the Online Repository at www.jacionline.org
). In a sensitivity analysis, removing sensitization to the one food allergen (egg white) did not materially change the results (data not shown).