Department of Obstetrics and Gynecology, University of São Paulo, São Paulo, Brazil.
Ultrasound Obstet Gynecol. 2012 Mar;39(3):274-8. doi: 10.1002/uog.9024. Epub 2012 Feb 10.
Genetic sonography following first-trimester combined screening appears to increase substantially detection rates for Down syndrome but it relies on the unproved assumption of independence between these tests. In this study we aimed to investigate the relationship between first-trimester nuchal translucency (NT) and a series of second-trimester soft markers and structural defects in unaffected pregnancies.
NT measurement in the first trimester was followed by second-trimester scan (18 to 23 + 6 weeks) including examination for three categorical markers (intracardiac echogenic foci, hyperechogenic bowel and structural defects) and measurement of nasal bone length, nuchal-fold thickness, femur length, humerus length, renal pelvis diameter and prenasal thickness. All continuous variables were expressed in multiples of the median (MoM) for gestation and correlation coefficients between log-transformed NT and second-trimester variables were calculated. In addition, frequencies of soft markers and structural defects in cases with increased NT were compared to those with normal NT, using MoM cut-offs.
In a dataset of 1970 cases, NT was significantly correlated (P < 0.05) with all second-trimester continuous variables, the correlation being strongest for nuchal-fold thickness (r = 0.10). There was a higher frequency of cases with second-trimester nuchal-fold thickness above the 97.5(th) centile (10.7 vs. 2.2%) and hyperechogenic bowel (2.4 vs. 0.1%) in cases with increased NT.
Straightforward reassessment of risk using likelihood ratios derived from the second-trimester genetic sonogram might lead to inaccurate estimates. Multivariate models using continuous second-trimester variables might be preferable in sequential screening strategies.
早孕期联合筛查后的基因超声检查似乎显著提高了唐氏综合征的检出率，但这依赖于这些检查之间独立性的未经证实的假设。本研究旨在调查正常妊娠中早孕期颈项透明层（NT）与一系列中孕期软指标和结构缺陷之间的关系。
在早孕期进行 NT 测量，随后进行中孕期超声检查（18 至 23+6 周），包括检查三个分类标记物（心内强回声灶、肠回声增强和结构缺陷）和测量鼻骨长度、颈项皱褶厚度、股骨长度、肱骨长度、肾盂直径和鼻前厚度。所有连续变量均表示为妊娠中位数的倍数（MoM），并计算 NT 与中孕期变量的对数转换后的相关系数。此外，使用 MoM 截断值比较 NT 增加的病例与 NT 正常的病例的软指标和结构缺陷的频率。
在 1970 例病例的数据集，NT 与所有中孕期连续变量均显著相关（P<0.05），与颈项皱褶厚度的相关性最强（r=0.10）。NT 增加的病例中，中孕期颈项皱褶厚度超过第 97.5 百分位（10.7%比 2.2%）和肠回声增强（2.4%比 0.1%）的病例频率更高。
使用中孕期遗传超声检查得出的似然比直接重新评估风险可能导致不准确的估计。在连续筛查策略中，使用连续中孕期变量的多变量模型可能更可取。
