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Comparison of birth weight distributions between Chinese and Caucasian infants
S W Wen1, M S Kramer, R H Usher
1Department of Epidemiology and Biostatistics, McGill University Faculty of Medicine, Montreal, Quebec, Canada.
Insights
Chinese infants have lower birth weights due to differences in fetal growth patterns, not gestational duration. Their growth is faster early in the third trimester but slower near and after term, contributing to a tighter birth weight distribution.
Area of Science:
- Perinatal epidemiology
- Human growth and development
- Anthropology
Background:
- Birth weight distributions exhibit ethnic variations, notably between Chinese and Caucasian populations.
- Understanding these differences is crucial for perinatal health assessments and interventions.
Purpose of the Study:
- To investigate the underlying causes of Chinese-Caucasian disparities in infant birth weight.
- To differentiate the roles of fetal growth patterns versus gestational duration in these ethnic variations.
Main Methods:
- A comparative cohort study involving Caucasian, immigrant Chinese, and native Chinese infants.
- Analysis of birth weights, fetal growth ratios, and gestational ages across diverse populations.
- Exclusion of mothers with extreme demographic, anthropometric, nutritional, and lifestyle factors.
Main Results:
- Chinese infants exhibited significantly lower mean birth weights and fetal growth ratios compared to Caucasians.
- No consistent ethnic differences in gestational age were observed.
- Race-specific fetal growth rates varied by gestation: Chinese infants showed faster early third-trimester growth but slower late-term growth.
Conclusions:
- Lower mean birth weight in Chinese infants is primarily attributed to distinct fetal growth trajectories, not shorter gestation.
- The tighter birth weight distribution in Chinese infants results from both environmental influences and inherent growth patterns.
- Ethnic differences in fetal growth, particularly during late gestation, are key determinants of birth weight variations.
Abstract:
To assess the reasons for the Chinese-Caucasian differences in birth weight distributions, a cohort study was carried out involving 18,665 Caucasian and 1,597 immigrant Chinese infants born at Montreal's Royal Victoria Hospital from January 1978 to March 1990 and 1,862 native Chinese infants born at Hefei Maternal and Infant Hospital in Hefei, People's Republic of China, from September 1990 to August 1991. Mean (standard deviation) birth weights in grams were 3,369 (567), 3,195 (493), and 3,171 (428) (p < 0.01 for differences in mean and variance), and mean (standard deviation) fetal growth ratios (ratio of observed birth weight to average birth weight at the same gestational age) were 0.994 (0.124), 0.963 (0.114), and 0.935 (0.112) (p < 0.01 for differences in mean and variance), respectively, in the Caucasian, immigrant Chinese, and native Chinese groups. No important or consistent Chinese-Caucasian differences in gestational age were found. When mothers with extreme values for demographic, anthropometric, nutritional, and lifestyle determinants of fetal growth were excluded, the mean fetal growth ratio in Caucasian infants remained significantly higher (p < 0.01), but the standard deviations became more similar (p > 0.05): Mean (standard deviation) fetal growth ratios were 1.001 (0.111), 0.966 (0.108), and 0.946 (0.114), respectively. The race-specific rate of growth differed according to period of gestation, with Chinese infants showing more rapid fetal growth early in the third trimester but slower growth near and after term. The authors conclude that the lower mean birth weight in Chinese infants is due to differences in fetal growth (rather than gestational duration) and by their inherently slower growth at or after term. The tight distribution of birth weight among the Chinese is caused partly by their reduced exposure to extremes of maternal determinants of fetal growth (mediated largely by environmental mechanisms) and partly by their inherently different growth pattern, with faster growth at earlier gestations but slower growth at later gestations.