Objective: To probe into the similarities and differences of birth weight by gestational age between China and the United States by a comparative study.
Methods: For China, we used the records of 24,150 single livebirth neonates. These records were collected between February 1986 and May 1987 from 43 hospitals and health care units in 15 large and middle cities in the South and North of China. For the United States, we used the natal records of National Center for Health Statistics from 1980 to 1987, selecting infants whose parents were coded as white and with higher socioeconomic backgrounds in the birth records. A total of 6,295,102 singleton livebirth neonates were selected. We used a method based on probability plots to define birth weight distributions.
Results: The 50th and 95th percentiles of birth weights by gestational age of American newborns with white parents were more than those of Chinese newborns. The 50th percentile values of birth weights of American male and female newborns were 357 g and 277 g (about 10% and 8% respectively of the birth weight of a term newborn) more than those of Chinese male and female newborns respectively at 40 weeks of GA.
Conclusions: American white newborns were heavier than Chinese newborns. The differences were mainly due to race-specific influences, and were related to the differences in socioeconomic and educational background. We suggest that the references of birth weight by gestational age should be formulated separately in China and in the U.S.