Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; Ontario Fetal Centre, Toronto, Ontario, Canada.
Fetal Medicine Unit, Department of Obstetrics and Gynaecology, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; Ontario Fetal Centre, Toronto, Ontario, Canada.
Am J Obstet Gynecol MFM. 2022 Mar;4(2S):100520. doi: 10.1016/j.ajogmf.2021.100520. Epub 2021 Oct 30.
Monoamniotic twin pregnancies are rare, but early diagnosis of such pregnancies is critical, as the incidence of complications in these pregnancies is much higher than in diamniotic or dichorionic twin pregnancies. Overall, only 70% of all monoamniotic twins will survive. Furthermore, approximately half of fetal deaths in these pregnancies are because of the high incidence of fetal anomalies (15%-25%), such as twin reversed arterial perfusion sequence and conjoined twinning. Therefore, early anatomy screening in the first trimester of pregnancy is recommended. Other causes of fetal death in these pregnancies include twin-twin transfusion syndrome, tight cord entanglement, or acute hemodynamic imbalances through the large placental vascular anastomoses. After viability, fetal surveillance can be intensified, as this decreases the risk of in utero death. Both inpatient and outpatient surveillance are reasonable. If otherwise uncomplicated, monoamniotic twins should be delivered at 33 to 34 weeks' gestation. Most centers will deliver by cesarean delivery, but some continue to advocate for vaginal delivery. Lastly, neonatal morbidity is high in monoamniotic twin pregnancies and is mainly related to prematurity.
单羊膜囊双胎妊娠较为罕见，但早期诊断此类妊娠至关重要，因为此类妊娠的并发症发生率远高于双羊膜囊或双绒毛膜双胎妊娠。总体而言，只有 70%的单羊膜囊双胎能够存活。此外，这些妊娠中约有一半的胎儿死亡是由于胎儿畸形的高发（15%-25%），例如双胎反向动脉灌注序列和联体双胎。因此，建议在妊娠早期进行早期解剖筛查。这些妊娠中其他导致胎儿死亡的原因包括双胎输血综合征、脐带缠绕过紧，或通过大胎盘血管吻合导致急性血流动力学失衡。在有生存能力后，可以加强胎儿监测，因为这可以降低宫内死亡的风险。住院和门诊监测都是合理的。如果没有其他并发症，单羊膜囊双胎应在 33 至 34 周时分娩。大多数中心会选择剖宫产，但也有一些中心继续提倡阴道分娩。最后，单羊膜囊双胎妊娠的新生儿发病率较高，主要与早产有关。
