Nuffield Department of Obstetrics & Gynaecology and Oxford Maternal & Perinatal Health Institute (OMPHI), Green Templeton College, University of Oxford, Level 3 Women's Centre, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK.
BMC Med Res Methodol. 2013 Dec 7;13:151. doi: 10.1186/1471-2288-13-151.
Fetal ultrasound scanning is considered vital for routine antenatal care with first trimester scans recommended for accurate estimation of gestational age (GA). A reliable estimate of gestational age is key information underpinning clinical care and allows estimation of expected date of delivery. Fetal crown-rump length (CRL) is recommended over last menstrual period for estimating GA when measured in early pregnancy i.e. 9+0-13+6 weeks.
The INTERGROWTH-21st Project is the largest prospective study to collect data on CRL in geographically diverse populations and with a high level of quality control measures in place. We aim to develop a new gestational age estimation equation based on the crown-rump length (CRL) from women recruited between 9+0-13+6 weeks. The main statistical challenge is modelling data when the outcome variable (GA) is truncated at both ends, i.e. at 9 and 14 weeks.We explored three alternative statistical approaches to overcome the truncation of GA. To evaluate these strategies we generated a data set with no truncation of GA that was similar to the INTERGROWTH-21st Project CRL data, which we used to explore the performance of different methods of analysis of these data when we imposed truncation at 9 and 14 weeks of gestation. These 3 methods were first tested in a simulation based study using a previously published dating equation by Verburg et al. and evaluated how well each of them performed in relation to the model from which the data were generated. After evaluating the 3 approaches using simulated data based on the Verburg equations, the best approach will be applied to the INTERGROWTH-21st Project data to estimate GA from CRL.
Results of these rather "ad hoc" statistical methods correspond very closely to the "real data" for Verburg, a data set that is similar to the INTERGROWTH-21st project CRL data set.
We are confident that we can use these approaches to get reliable estimates based on INTERGROWTH-21st Project CRL data. These approaches may be a solution to other truncation problems involving similar data though their application to other settings would need to be evaluated.
胎儿超声扫描被认为是常规产前护理的重要手段，建议在孕早期进行扫描，以准确估计胎龄（GA）。准确估计胎龄是临床护理的关键信息，可用于估计预期分娩日期。当在孕早期（即 9+0-13+6 周）测量时，胎儿头臀长（CRL）比末次月经更适合用于估计 GA。
INTERGROWTH-21st 项目是最大的前瞻性研究，旨在收集地理上多样化人群的 CRL 数据，并采用高质量控制措施。我们的目标是基于在 9+0-13+6 周之间招募的女性的头臀长（CRL），制定一个新的胎龄估计方程。主要的统计挑战是在结局变量（GA）在两端截断的情况下建模数据，即在 9 周和 14 周截断。我们探索了三种替代的统计方法来克服 GA 的截断。为了评估这些策略，我们生成了一个没有 GA 截断的数据集，该数据集与 INTERGROWTH-21st 项目的 CRL 数据相似，我们使用该数据集来探索在将截断施加到 9 周和 14 周妊娠时，对这些数据进行不同分析方法的性能。这 3 种方法首先在一项基于模拟的研究中使用 Verburg 等人之前发表的约会方程进行了测试，并评估了它们各自在与数据生成模型的关系中表现如何。在使用基于 Verburg 方程的模拟数据评估了这 3 种方法之后，将最佳方法应用于 INTERGROWTH-21st 项目数据，以从 CRL 估计 GA。
这些相当“特定用途”的统计方法的结果与“真实数据”非常吻合，该数据类似于 INTERGROWTH-21st 项目的 CRL 数据集。
我们有信心可以使用这些方法基于 INTERGROWTH-21st 项目的 CRL 数据获得可靠的估计值。这些方法可能是解决涉及类似数据的其他截断问题的一种解决方案，但需要对其在其他环境中的应用进行评估。
