Chapter 7 Growth velocity

7.1 Overview

Purpose:

The primary manuscript documents the population intervention effects of different child, parental, and household risk factors on absolute child Z-scores at different ages. Here, we present the difference in linear and ponderal growth velocities between the observed mean velocities and the estimated mean velocities if the exposures were shifted to the low-risk level. We calculated the change in LAZ, WAZ, length in centimeters, and weight in kilograms within 3-month age intervals, including measurements within a two-week window around each age in months to account for variation in the age of each length measurement.

Interpretation:

Most risk factors were not significantly associated with increased growth.

Implications:

An important finding relates to the associations between maternal anthropometry, birth anthropometry, and catch-up growth. We found that maternal anthropometry is generally not associated with growth velocity, consistent with the mostly parallel growth trajectories shown in Figure 3, except for associations between maternal height and early growth.

Mother’s height was strongly associated with all 4 measures of growth velocity in the first 3 months of life. Taller mothers gave birth to infants who grew faster (PIE: 0.017 [95% CI: 0.028, 0.006] for LAZ velocity. This is also noticeable in Figure 3a, where growth faltering as measured by change in LAZ is lower in the first 3 months for children of taller mothers than for children of shorter mothers. After 3 months, maternal height had non-significant or very small effects on LAZ, WAZ, height, and weight velocities.

Mother’s weight was not associated with LAZ or WAZ velocities but was associated with increased length velocity for most age categories after 6 months and weight velocities before 15 months. Higher maternal BMI was associated with a decreased LAZ velocity before 3 months and increased weight velocity before 6 months, but not with other ages or measures of growth velocity.

7.2 Age-stratified population attributable differences in change in length-for-age Z-scores over 3-month age bands.

Exposures, rank ordered by pooled population attributable difference on child LAZ velocities, stratified by the age of the child at the time of anthropometry measurements. The population attributable difference is the expected difference in population mean Z-score if all children had the reference level of the exposure rather than the observed distribution. For all plots, reference levels are printed next to the name of the exposure. Estimates are adjusted for all other measured exposures not on the causal pathway.

7.3 Age-stratified population attributable differences in change in weight-for-age Z-scores over 3-month age bands.

Exposures, rank ordered by pooled population attributable difference on child WAZ velocities, stratified by the age of the child at the time of anthropometry measurements. The population attributable difference is the expected difference in population mean Z-score if all children had the reference level of the exposure rather than the observed distribution. For all plots, reference levels are printed next to the name of the exposure. Estimates are adjusted for all other measured exposures not on the causal pathway.

7.4 Age-stratified population attributable differences in change in child length over 3-month age bands.

Exposures, rank ordered by pooled population attributable difference on child length velocities, stratified by the age of the child at the time of anthropometry measurements. The population attributable difference is the expected difference in population mean differences in lengths (cm) if all children had the reference level of the exposure rather than the observed distribution. For all plots, reference levels are printed next to the name of the exposure. Estimates are adjusted for all other measured exposures not on the causal pathway.

7.5 Age-stratified population attributable differences in change in child weight over 3-month age bands.

Exposures, rank ordered by pooled population attributable difference on child length velocities, stratified by the age of the child at the time of anthropometry measurements. The population attributable difference is the expected difference in population mean differences in lengths (cm) if all children had the reference level of the exposure rather than the observed distribution. For all plots, reference levels are printed next to the name of the exposure. Estimates are adjusted for all other measured exposures not on the causal pathway.