Longitudinal associations of gross motor development, motor milestone achievement and weight-for-length z score in a racially diverse cohort of US infants

Objectives

To investigate longitudinal associations between gross motor development, motor milestone achievement and weight-for-length z scores in a sample of infants. In a secondary aim, we explored potential bidirectional relationships, as higher weight-for-length z scores may impede motor development, and poor motor development may lead to obesity.

Design

The design was an observational birth cohort.

Setting

We used data from the Nurture study, a birth cohort of predominately black women and their infants residing in the Southeastern USA.

Participants

666 women enrolled their infants in Nurture. We excluded infants with missing data on exposure, outcome or main covariates, leaving a total analytic sample of 425 infants.

Primary outcome

The outcome was weight-for-length z score, measured when infants were 3, 6, 9 12 months.

Results

Among infants, 64.7% were black, 18.8% were white and 16.9% were other/multiple race. Mean (SD) breastfeeding duration was 17.6 (19.7) weeks. Just over one-third (38.5%) had an annual household income of < $20 000. After adjusting for potential confounders, higher motor development score was associated with lower weight-for-length z score (–0.004; 95% CI –0.001 to –0.007; p=0.01), mainly driven by associations among boys (–0.007; 95% CI –0.014 to –0.001; p=0.03) and not girls (0.001; 95% CI –0.005 to 0.008; p=0.62). Earlier crawling was the only milestone associated with a lower weight-for-length z score at 12 months (–0.328; 95% CI –0.585 to 0.072; p=0.012). However, this association appeared to be driven by male infants only (–0.461; 95% CI –0.825 to –0.096; p=0.01). Weight-for-length z score was unrelated to subsequent motor development score and was thus not bidirectional in our sample.

Conclusions

Higher motor development score and earlier crawling were associated with lower subsequent weight-for-length z score. However, this was primary true for male infants only. These findings contribute to the growing body of evidence suggesting that delayed motor development may be associated with later obesity.

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