Division of Perinatology, Fetal Diagnosis and Therapy, Maternal and Perinatal Care Center, Seirei Hamamatsu General Hospital, Naka-ku, Hamamatsu City, Japan.
Ultrasound Obstet Gynecol. 2010 Sep;36(3):384-6. doi: 10.1002/uog.7710.
The exact determination of amnionicity is a major issue for the clinical management of monochorionic twin pregnancies, due to the high risk of perinatal mortality and morbidity in monochorionic monoamniotic (MCMA) twins. Counting the number of yolk sacs is believed to be a good indicator of amnionicity in the early first trimester, and it has previously been suggested that the number of yolk sacs is equal to amnionicity in both MCMA and monochorionic diamniotic twin pregnancies. However, the accuracy of the relationship between number of yolk sacs and amnionicity has recently been called into question. To the best of our knowledge, no previous reports have shown two yolk sacs in MCMA twin pregnancies. We report two cases of MCMA twins with two yolk sacs on first-trimester ultrasonography, and confirmed monoamnionicity in the second trimester showing umbilical cord entanglement. Postnatal examination showed an MCMA placenta in both cases, and entangled umbilical cords confirmed monoamnionicity. The possibility of monoamnionicity must still be suspected when two yolk sacs are detected early in the first trimester on ultrasound examination in monochorionic twin pregnancies.
羊膜性的确切确定是单绒毛膜双胎妊娠临床管理的一个主要问题，因为单绒毛膜单羊膜（MCMA）双胞胎围产期死亡率和发病率高。在孕早期，计算卵黄囊的数量被认为是羊膜性的一个很好的指标，并且以前有人认为 MCMA 和单绒毛膜双羊膜双胞胎妊娠中卵黄囊的数量等于羊膜性。然而，最近人们对卵黄囊数量与羊膜性之间的关系的准确性提出了质疑。据我们所知，以前没有报告显示 MCMA 双胎妊娠中有两个卵黄囊。我们报告了两例 MCMA 双胞胎在孕早期超声检查中均有两个卵黄囊，在孕中期证实为单羊膜性，表现为脐带缠绕。产后检查显示两例均为 MCMA 胎盘，缠绕的脐带证实为单羊膜性。在单绒毛膜双胎妊娠的孕早期超声检查中，如果早期发现两个卵黄囊，仍必须怀疑为单羊膜性。
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