McKenna K M, Feldstein V A, Goldstein R B, Filly R A
Department of Radiology, University of California, San Francisco 94143-0628, USA.
J Ultrasound Med. 1995 Feb;14(2):117-21. doi: 10.7863/jum.1995.14.2.117.
Between 6.5 to 10 weeks of gestation, the length of the amniotic cavity is similar to that of the embryo. It follows that by the time an amniotic sac is detectable sonographically, an embryo of equal length should also be visualized. Retrospective review of case records at our institution revealed 15 patients in whom the amnion was visualized in the absence of an embryonic pole during first trimester sonography (endovaginal and transvesical). Indications for sonographic examination included gestational age estimation, discrepant size and dates, or vaginal bleeding. The mean sac diameter for the 15 gestations ranged from 14 to 36 mm, corresponding to gestational ages of 6.1 to 9.5 weeks. Ages based on the last menstrual period ranged from 6.1 to 11 weeks. A yolk sac was identified in all cases in addition to the amniotic sac, but neither an embryo nor cardiac pulsations were observed. In 12 of the 15 cases the size of the gestational sac was greater than 16 mm, such that the absence of an embryo also met an accepted criterion for a failed pregnancy. Follow-up in all cases confirmed early pregnancy failure. In this series the demonstration of an "empty amnion" (visualization of an amnion but no identifiable embryonic pole) was always associated with pregnancy loss. The "empty amnion" sign is helpful as an additional finding confirming early pregnancy failure.
在妊娠6.5至10周之间，羊膜腔的长度与胚胎的长度相似。因此，当通过超声检查可检测到羊膜囊时，同样长度的胚胎也应该能够被看到。对我们机构病例记录的回顾性研究发现，有15例患者在孕早期超声检查（经阴道和经膀胱）时可见羊膜，但未见胚胎极。超声检查的指征包括估计孕周、大小与孕周不符或阴道出血。这15例妊娠的羊膜囊平均直径为14至36毫米，对应的孕周为6.1至9.5周。根据末次月经计算的孕周为6.1至11周。除羊膜囊外，所有病例均可见卵黄囊，但未观察到胚胎或心搏。15例中有12例妊娠囊大小大于16毫米，因此未见到胚胎也符合公认的妊娠失败标准。所有病例的随访均证实为早期妊娠失败。在本系列中，“空羊膜”（可见羊膜但未见可识别的胚胎极）的表现总是与妊娠丢失相关。“空羊膜”征作为确认早期妊娠失败的额外发现很有帮助。
