Wen Shi Wu, Kramer Michael S, Platt Robert, Demissie Kitaw, Joseph K S, Liu Shiliang, Sauve Reg
Department of Obstetrics and Gynecology and Clinical Epidemiology Program, University of Ottawa, Ontario, Canada.
Paediatr Perinat Epidemiol. 2003 Oct;17(4):347-54. doi: 10.1046/j.1365-3016.2003.00513.x.
Preterm birth and low birthweight in Canada have shown paradoxical temporal trends, with an increase in preterm birth and a decrease in low birthweight. Mean birthweight has increased in many industrialised countries, despite a recent rise in preterm birth, suggesting a temporal increase in fetal growth (birthweight for gestational age) in Canada. We thus described temporal trends in the distribution of fetal growth from 1981 to 1997, including means and proportions of infants at both the low and high ends of the fetal growth distribution. We used data for singleton live births from Statistics Canada's Canadian Birth Data Base for the years 1981-97 (excluding Ontario and Newfoundland) and analysed temporal trends in birthweight and birthweight-for-gestational-age z-score as continuous outcomes and the derived dichotomised outcomes [i.e. low birthweight (<2500 g), very low birthweight (<1500 g), small-for-gestational-age (<10th percentile), very small-for-gestational-age (<3rd percentile), high birthweight (>4000 g), very high birthweight (>4500 g), large-for-gestational-age (>90th percentile), and very large-for-gestational-age (>97th percentile)]. The birthweight-for-gestational-age was based on a newly developed population-based Canadian reference. The results showed that in the overall sample and in a subsample of term and post-term births, mean birthweight, mean z-score, rates of high birthweight, very high birthweight, large-for-gestational-age, and very large-for-gestational-age increased whereas rates of low birthweight, very low birthweight, small-for-gestational-age, and very small-for-gestational-age decreased between 1981-83 and 1995-97. The reverse was observed in preterm births. These temporal changes were larger for more extremely distributed measures of fetal growth. For example, compared with 1981-83, the decrease in 1995-97 for very small-for-gestational-age (<3rd percentile) was 38.9%, whereas the decrease for small-for-gestational-age (<10th percentile) was only 29.7%. Corresponding temporal increases were 21.4% for very large-for-gestational-age (>97th percentile) and 15.2% for large-for-gestational-age (>90th percentile). Among infants with gestational age 34-36 weeks, all measures of fetal growth, including the rates for all dichotomous outcomes, decreased in 1995-97 as compared with 1981-83. We conclude that Canadian infants are getting bigger, but only those born at term. The temporal trends for more extremely distributed fetal growth measures are particularly marked.
加拿大的早产和低出生体重呈现出矛盾的时间趋势，早产率上升而低出生体重率下降。尽管近期早产率有所上升，但许多工业化国家的平均出生体重有所增加，这表明加拿大胎儿生长（按孕周计算的出生体重）在时间上有所增加。因此，我们描述了1981年至1997年胎儿生长分布的时间趋势，包括胎儿生长分布两端的婴儿的平均值和比例。我们使用了加拿大统计局加拿大出生数据库中1981 - 1997年（不包括安大略省和纽芬兰省）单胎活产的数据，并分析了出生体重和按孕周计算的出生体重z分数作为连续结果以及派生的二分结果[即低出生体重（<2500克）、极低出生体重（<1500克）、小于胎龄（<第10百分位数）、极小于胎龄（<第3百分位数）、高出生体重（>4000克）、极高出生体重（>4500克）、大于胎龄（>第90百分位数）和极大于胎龄（>第97百分位数）]的时间趋势。按孕周计算的出生体重基于新开发的以人群为基础的加拿大参考标准。结果表明，在总体样本以及足月和过期产的子样本中，1981 - 1983年至1995 - 1997年期间，平均出生体重、平均z分数、高出生体重、极高出生体重、大于胎龄和极大于胎龄的发生率增加，而低出生体重、极低出生体重、小于胎龄和极小于胎龄的发生率下降。在早产中观察到相反的情况。对于胎儿生长分布更极端的测量指标，这些时间变化更大。例如，与1981 - 1983年相比，1995 - 1997年极小于胎龄（<第3百分位数）的下降率为38.9%，而小于胎龄（<第10百分位数）的下降率仅为29.7%。极大于胎龄（>第97百分位数）和大于胎龄（>第90百分位数）的相应时间增加率分别为21.4%和15.2%。在孕周为34 - 36周的婴儿中，与1981 - 1983年相比，1995 - 1997年所有胎儿生长指标，包括所有二分结果的发生率都下降了。我们得出结论，加拿大婴儿出生时体重越来越大，但仅指足月出生的婴儿。胎儿生长分布更极端测量指标的时间趋势尤为明显。
