Institute of Reproductive and Developmental Biology (IRDB), Imperial College London, London, UK.
Ultrasound Obstet Gynecol. 2011 Nov;38(5):497-502. doi: 10.1002/uog.10109. Epub 2011 Oct 13.
There is significant variation in cut-off values for mean gestational sac diameter (MSD) and embryo crown-rump length (CRL) used to define miscarriage, values suggested in the literature ranging from 13 to 25 mm for MSD and from 3 to 8 mm for CRL. We aimed to define the false-positive rate (FPR) for the diagnosis of miscarriage associated with different CRL and MSD measurements with or without a yolk sac in a large study population of patients attending early pregnancy clinics. We also aimed to define cut-off values for CRL and MSD that, on the basis of a single measurement, can definitively diagnose a miscarriage and so exclude possible inadvertent termination of pregnancy.
This was an observational cross-sectional study. Data were collected prospectively according to a predefined protocol. Intrauterine pregnancy of uncertain viability (IPUV) was defined as an empty gestational sac or sac with a yolk sac but no embryo seen with MSD < 20 or < 30 mm or an embryo with an absent heartbeat and CRL < 6 mm or < 8 mm. We recruited to the study 1060 consecutive women with IPUV. The endpoint was presence or absence of a viable pregnancy at the time of first-trimester screening ultrasonography between 11 and 14 weeks. The sensitivity, specificity, positive and negative predictive values were calculated for potential cut-off values to define miscarriage from MSD 8 to 30 mm with or without a yolk sac and from CRL 3 to 8 mm.
Of the 1060 women with a diagnosis of IPUV, 473 remained viable and 587 were non-viable by the time of the 11-14-week scan. In the absence of both embryo and yolk sac, the FPR for miscarriage was 4.4% when an MSD cut-off of 16 mm was used and 0.5% for a cut-off of 20 mm. There were no false-positive test results for miscarriage when a cut-off of MSD ≥ 21 mm was used. If a yolk sac was present but an embryo was not, the FPR for miscarriage was 2.6% for an MSD cut-off of 16 mm and 0.4% for a cut-off of 20 mm, with no false-positive results when a cut-off of MSD ≥ 21 mm was used. When an embryo was visible with an absent heartbeat, using a CRL cut-off of 4 mm the FPR for miscarriage was 8.3%, and for a CRL cut-off of 5 mm it was also 8.3%. There were no false-positive results using a CRL cut-off of ≥ 5.3 mm.
These data show that some current definitions used to diagnose miscarriage are potentially unsafe. Current national guidelines should be reviewed to avoid inadvertent termination of wanted pregnancies. An MSD cut-off of > 25 mm and a CRL cut-off of > 7 mm could be introduced to minimize the risk of a false-positive diagnosis of miscarriage.
用于定义流产的平均孕囊直径（MSD）和胚胎头臀长（CRL）的截断值存在显著差异，文献中建议的截断值范围为 MSD 为 13 至 25mm，CRL 为 3 至 8mm。我们旨在通过在一个大型的早孕诊所患者人群中进行的研究，定义不同 CRL 和 MSD 测量值（有或无卵黄囊）与流产相关的假阳性率（FPR）。我们还旨在定义 CRL 和 MSD 的截断值，这些截断值可以基于单次测量来明确诊断流产，从而排除可能的意外妊娠终止。
这是一项观察性的横断面研究。数据是按照预先制定的方案前瞻性收集的。宫内妊娠不确定是否存活（IPUV）定义为孕囊<20mm 或<30mm 时仅见空孕囊或孕囊伴卵黄囊，但未见胚胎，或孕囊见胚胎且无心搏，CRL<6mm 或<8mm。我们共招募了 1060 例有 IPUV 的连续女性患者。主要终点是在 11-14 周的早孕期超声筛查时，首次发现胚胎存活的情况。计算了 MSD 8 至 30mm（有或无卵黄囊）和 CRL 3 至 8mm 时，可能定义流产的潜在截断值的灵敏度、特异性、阳性预测值和阴性预测值。
在 1060 例被诊断为 IPUV 的女性中，473 例在 11-14 周超声检查时仍存活，587 例为非存活。如果没有胚胎和卵黄囊，当使用 16mm 的 MSD 截断值时，流产的 FPR 为 4.4%，当使用 20mm 的 MSD 截断值时，FPR 为 0.5%。当使用 MSD≥21mm 的截断值时，没有出现假阳性的流产试验结果。如果仅见卵黄囊但未见胚胎，当使用 16mm 的 MSD 截断值时，流产的 FPR 为 2.6%，当使用 20mm 的 MSD 截断值时，FPR 为 0.4%，当使用 MSD≥21mm 的截断值时，没有出现假阳性的结果。当胚胎可见且无心搏时，使用 CRL 截断值为 4mm 时，流产的 FPR 为 8.3%，使用 CRL 截断值为 5mm 时，FPR 也为 8.3%。当使用 CRL 截断值≥5.3mm 时，没有假阳性结果。
这些数据表明，目前用于诊断流产的一些定义可能存在安全风险。应该审查当前的国家指南，以避免意外终止想要的妊娠。引入 MSD 截断值>25mm 和 CRL 截断值>7mm 可以将假阳性诊断流产的风险最小化。
