Sex differences in the application of WHO standards to Shanghai infants from birth to 18 months.

ABSTRACT

BACKGROUND: The number of obese children in Shanghai has increased annually. Shanghai growth standards are higher than the World Health Organization's (WHO's) growth standards, which may influence caregiver feeding practices and enhance the risk of overweight in infants. METHOD: A cluster-randomized controlled trial analysed 15,019 infants (healthy newborns, ≥3 clinical consultations in one year) from 19 community health service centers in two urban areas in Shanghai. Randomization was performed at the community level. A total of 8510 infants in the S-group were assessed with the Shanghai growth standards, and 6509 infants in the W-group were assessed by the WHO growth standards. Follow-up data were collected at 1, 2, 4, 6, 9, 12 and 18 months. Changes in the weight-for-age z score (WAZ), length-for-age z score (LAZ), and weight-for length z score (WLZ) were assessed using mixed regression models. Sex differences were compared between groups at all follow-up periods. RESULTS: Compared to the S-group, the percent of overweight in boys in the W-group significantly decreased starting at 9 months (4.9% vs 3.3%, P = 0.011 at 9 months, 4.5% vs 2.5%, P < 0.001 at 12 months and 3.1% vs 0.8%, P < 0.001 at 18 months), and the percent of overweight in girls in the W-group significantly decreased starting at 12 months (3.0% vs 1.8%, P = 0.009 at 12 months and 1.7% vs 0.6%, P = 0.039 at 18 months). A decreased weight in boys (from 4 months to 18 months, P < 0.05) and an increased length in girls (from 6 months to 18 months, P < 0.05) were the key reasons for the decreased overweight percentage in the W-group. CONCLUSION: The adoption of the WHO growth standards could result in markedly decreased weight gain in boys and increased length gain in girls beyond the age of 18 months among urban Shanghai infants. TRIAL REGISTRATION NUMBER ChiCTR1800015371.