Nuffield Department of Obstetrics & Gynaecology, University of Oxford, Oxford, UK.
BJOG. 2014 Apr;121(5):556-65. doi: 10.1111/1471-0528.12478. Epub 2014 Jan 6.
Fetal crown-rump length (CRL) measurement by ultrasound in the first trimester is the standard method for pregnancy dating; however, a multitude of CRL equations to estimate gestational age (GA) are reported in the literature.
To evaluate the methodological quality used in studies reporting CRL equations to estimate GA using a set of predefined criteria.
Searches of MEDLINE, EMBASE, and CINAHL databases, from 1948 to 31 January 2011, and secondary reference sources, were performed.
Observational ultrasound studies, where the primary aim was to create equations for GA estimation using a CRL measurement.
Included studies were scored against predefined independently agreed methodological criteria: an overall quality score was calculated for each study.
The searches yielded 1142 citations. Two reviewers screened the papers and independently assessed the full-text versions of 29 eligible studies. The highest potential for bias was noted in inclusion and exclusion criteria, and in maternal demographic characteristics. No studies had systematic ultrasound quality-control measures. The four studies with the highest scores (lowest risk of bias) satisfied 18 or more of the 29 criteria; these showed lower variation in GA estimation than the remaining, lower-scoring studies. This was particularly evident at the extremes of GA.
AUTHOR'S CONCLUSIONS: Considerable methodological heterogeneity and limitations exist in studies reporting CRL equations for estimating GA, and these result in a wide range of estimated GAs for any given CRL; however, when studies with the highest methodological quality are used, this range is reduced.
超声测量胎儿头臀长（CRL）是确定妊娠时间的标准方法，但文献中报道了许多用于估计孕龄（GA）的CRL 方程。
用一组预定标准评价报道用于估计 GA 的 CRL 方程的研究中的方法学质量。
检索 MEDLINE、EMBASE 和 CINAHL 数据库，检索时间从 1948 年到 2011 年 1 月 31 日，同时也检索了二级参考文献。
观察性超声研究，其主要目的是通过 CRL 测量建立 GA 估计方程。
对纳入的研究根据预先确定的独立同意的方法学标准进行评分：为每个研究计算一个总体质量评分。
检索得到 1142 条引用文献。两位评审员筛选文献并独立评估了 29 篇合格研究的全文版本。纳入和排除标准以及孕妇的人口统计学特征方面存在最大的偏倚风险。没有研究有系统的超声质量控制措施。四个评分最高（偏倚风险最低）的研究满足 29 项标准中的 18 项或更多项；这些研究在估计 GA 方面的变异性低于其他评分较低的研究。这种情况在 GA 的极端值时更为明显。
用于估计 GA 的 CRL 方程的研究中存在很大的方法学异质性和局限性，这导致对于任何给定的 CRL 会有广泛的估计 GA；然而，当使用方法学质量最高的研究时，这个范围会缩小。
