From the Centre for Fertility and Health, Norwegian Institute of Public Health, Oslo, Norway.
MRC Integrative Epidemiology Unit, University of Bristol, Bristol, United Kingdom.
Epidemiology. 2020 Jul;31(4):587-594. doi: 10.1097/EDE.0000000000001211.
There was a distinct rise in mean birthweights in Norway starting in 1991 that plateaued in 1996-2002 and then declined to previous levels. We investigated whether these changes corresponded to trends in neonatal mortality or other birthweight-associated pregnancy outcomes. We also explored known predictors of birthweight and examined whether these could explain the birthweight trends.
We calculated mean birthweight for all live births in Norway in each year from 1982 to 2016, together with annual neonatal mortality and proportion of infants born preterm, or with low Apgar score. We stratified mean birthweight over time by factors including parity, gestational age, and Scandinavian versus non-Scandinavian origin of mother, to test robustness of the pattern. In addition, we used multivariable linear regression to obtain adjusted estimates for mean birthweight per year.
A 50-g rise and fall of mean birthweights during a 25-year period was not accompanied by corresponding changes in neonatal mortality, preterm births, or Apgar scores. The distinct hump pattern was restricted to term births and was not apparent among infants of mothers born outside Scandinavia. We saw a similar pattern for Sweden but not Finland. Known predictors of birthweight (such as parity, mode of onset of delivery, and marital status) did not explain the hump.
A distinct temporal hump in mean birthweight among Norwegian term births had no obvious explanations. Furthermore, these fluctuations in birthweight were not associated indirectly with adverse outcomes in measures of infant health.
自 1991 年以来，挪威的平均出生体重明显上升，在 1996-2002 年达到峰值，随后下降到之前的水平。我们调查了这些变化是否与新生儿死亡率或其他与出生体重相关的妊娠结局趋势相对应。我们还探讨了已知的出生体重预测因素，并研究了这些因素是否可以解释出生体重趋势。
我们计算了 1982 年至 2016 年期间挪威每年所有活产儿的平均出生体重，以及每年的新生儿死亡率和早产儿比例，或低阿普加评分的婴儿比例。我们根据产妇的产次、胎龄、斯堪的纳维亚和非斯堪的纳维亚血统等因素对平均出生体重进行了时间分层，以检验该模式的稳健性。此外，我们使用多元线性回归获得了每年平均出生体重的调整估计值。
在 25 年的时间里，平均出生体重上升了 50 克，下降了 50 克，但新生儿死亡率、早产率或阿普加评分并没有相应变化。明显的驼峰模式仅限于足月出生，在非斯堪的纳维亚血统的母亲所生的婴儿中并不明显。我们在瑞典看到了类似的模式，但在芬兰没有。出生体重的已知预测因素（如产次、分娩方式和婚姻状况）并不能解释驼峰。
挪威足月出生的平均出生体重出现明显的时间驼峰，没有明显的解释。此外，这些出生体重的波动与婴儿健康指标的不良结局没有间接关联。
