Hemming Karla, Hutton Jane L, Bonellie Sandra
Department of Public Health, University of Birmingham, Birmingham B15 2TT, UK.
Eur J Obstet Gynecol Reprod Biol. 2009 Sep;146(1):41-5. doi: 10.1016/j.ejogrb.2009.05.033. Epub 2009 Jul 5.
We examined how customized birth-weight standards compare to population birth-weight references at term (> or =37 weeks), nearly term (34-36 weeks), moderately preterm (32-33 weeks) and for the very preterm births (28-31 weeks), with respect to perinatal mortality.
Data from the national Swedish Medical Births Register for the years 1992-2001, consisting of a total of 783,303 singletons born at or after 28 completed gestational weeks. Infants were classified as small for gestational age (SGA, <10th centile) according to a conventional population based birth-weight reference and a customized standard. Risk ratios (RR) for still birth and neonatal death were compared between standards by prematurity of the birth. Diagnostic performance measures of specificity, sensitivity and positive and negative predictive values were also evaluated.
More than half, 59% (209), of the 355 infants still-born between 28 and 31 weeks gestation were classified as SGA by the customized standard, but only 23% (80), were so classified as SGA by the population reference. However, only 14% (95%CI 13-16) of the 1461 very preterm infants classified as SGA by the customized standard were still-born, compared to 23% (95%CI 19-28) of the 348 infants classified as SGA by the population reference. Therefore, the relative risk of still birth for those classified as SGA by the customized standard is lower, 2.02 (95%CI: 1.65, 2.46), than for the population reference 2.64 (95%CI: 2.11, 3.30). Similar results were observed for the risk of neonatal death. For term weeks, customized standards showed stronger relationships than population references (RR: 4.30 (95%CI 3.82, 4.84) vs. 4.00 (95%CI 3.55, 4.51) for still births).
Customized standards categorize a higher absolute number of preterm infants who are still-born as SGA. However, infants classified as SGA by population references are at higher risk of perinatal mortality than infants classified as SGA by customized standards.
我们研究了定制的出生体重标准与足月（≥37周）、近足月（34 - 36周）、中度早产（32 - 33周）和极早产（28 - 31周）的人群出生体重参考标准在围产期死亡率方面的比较情况。
来自瑞典国家医疗出生登记处1992 - 2001年的数据，共包括783,303例孕满28周及以后出生的单胎婴儿。根据传统的基于人群的出生体重参考标准和定制标准，将婴儿分类为小于胎龄儿（SGA，<第10百分位数）。按出生的早产程度比较不同标准下死产和新生儿死亡的风险比（RR）。还评估了特异性、敏感性以及阳性和阴性预测值等诊断性能指标。
在妊娠28至31周之间死产的355例婴儿中，超过一半（59%，209例）按照定制标准被分类为小于胎龄儿，但按照人群参考标准只有23%（80例）被如此分类。然而，按照定制标准被分类为小于胎龄儿的1461例极早产婴儿中，只有14%（95%CI 13 - 16）死产，相比之下，按照人群参考标准被分类为小于胎龄儿的348例婴儿中有23%（95%CI 19 - 28）死产。因此，按照定制标准被分类为小于胎龄儿的死产相对风险较低，为2.02（95%CI：1.65，2.46），低于人群参考标准的2.64（95%CI：2.11，3.30）。在新生儿死亡风险方面也观察到类似结果。对于足月时，定制标准显示出比人群参考标准更强的关联（死产的RR：4.30（95%CI 3.82，4.84）对4.00（95%CI 3.55，4.51））。
定制标准将更多死产的早产婴儿绝对数量分类为小于胎龄儿。然而，按照人群参考标准被分类为小于胎龄儿的婴儿比按照定制标准被分类为小于胎龄儿的婴儿有更高的围产期死亡风险。
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