Update on the birth weight standard and its diagnostic value in small for gestational age (SGA) infants in China

To identify the difference between the current newborn birth weight standard and the previous standard in China, and to evaluate the diagnostic value of newborn birth weight in small for gestational age (SGA) infants.

A retrospective analysis was conducted of 112 441 delivery cases in 2011, from 39 hospitals at different levels in 14 provinces and autonomous regions. Cases with incomplete data, gestational age <24 weeks, or severe fetal malformations or fetal death were excluded. Data were recorded and entered on hard paper copies and into an online database. SPSS 18.0 and SAS 9.2 statistical software were used for data analysis.

This study included 109 004 valid cases with an average birth weight of 3226.02 ± 525.82 g. Birth weight changed significantly from 1988 for all gestational ages. In preterm infants with gestational age <37 weeks, birth weight for each gestational week was lower than that in the birth weight standard from 15 cities in China in 1988 (p < 0.001). Full-term infants with gestational ages from 37 to 41⁺⁶ weeks showed significantly higher average birth weights compared with the previous birth weight standards (p < 0.001). The birth weight standard in this study exhibited better correlations than did the previous standard with regard to the diagnoses of adverse pregnancy outcomes, including SGA infants, stillbirth, neonatal asphyxia, neonatal death and neonatal complications; with RR values of 18.843 (9.656-36.774; 95% CI), 33.125 (14.576-75.275), 24.254 (10.630-56.256) and 2.492 (0.328-18.909), respectively.

The current birth weight standard used in Chinese medical institutions was enacted in 1988. This is not suitable for today's socioeconomic and clinical requirements, and needs to be updated. Diagnosis of preterm infants with SGA based upon the updated demographic birth weight standard manifested higher accuracy and avoided unnecessary medical interventions. However, the updated demographic birth weight standards were no better diagnostically than the previous standard for full-term infants. Customized birth weight standards from larger sample sizes and multi-center studies will be necessary to determine the appropriate birth weight standards in developing countries.