Objective To analyze the birth weight status of newborns in Shanghai based on population-wide surveillance, establish a birth weight standard applicable to Shanghai, and construct birth weight curves for newborns at different gestational ages. Method Data on singleton births from 2004 to 2023 were collected from the Shanghai Birth Registration System. Newborns were weighed naked within 12 hours after birth, and gestational age was determined based on the mother's last menstrual period, first-trimester ultrasound, and postnatal gestational age assessment. A generalized additive model for location, scale, and shape (GAMLSS) was used to fit birth weight curves for newborns of both sexes at 24-42 weeks of gestation. Worm plots and residual plots were employed for local and global fit diagnostics, respectively. The optimal model, determined by minimizing the Akaike Information Criterion (AIC) and Schwarz Bayesian Criterion (SBC), was the Box-Cox t distribution combined with penalized B-spline smoothing. The results were compared with the 2022 national standard. Result A total of 3,531,063 newborns were initially included, and after applying inclusion/exclusion criteria, 3,338,459 newborns were analyzed : males 1,762,721 (52.8%) and females 1,575,738 (47.2%), with a male-to-female ratio of 1.12. The mean birth weight was 3334.66 ± 450.84 g (3 383.98 ± 457.10 g for males and 3 279.49 ± 437.19 g for females). Birth weight curves for newborns of both sexes at 24-42 weeks of gestation were established for Shanghai. The results showed that birth weight increased continuously with gestational age for both sexes, with significant growth before 38 weeks and a marked slowdown thereafter. Males consistently had higher birth weights than females, and the sex-based difference widened with advancing gestational age. Compared with the national standard, the overall trend was similar, but Shanghai newborns had significantly higher birth weights at 24-40 weeks, whereas weights at ≥41 weeks were lower than the national standard. Conclusion This study establishes sex-specific birth weight standards for newborns in Shanghai at different gestational ages, reflecting the characteristics of intrauterine growth levels in Shanghai. It highlights differences between Shanghai and national standards across gestational age ranges, providing a reference for clinical diagnosis of abnormal birth weight and assessment of neonatal growth and development.
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