OP19.05: Monochorionic monoamniotic twin pregnancies with two yolk sacs may not be a rare finding: a report of two cases

Abstract

Exact determination of amnionicity is a major issue for clinical management of monochorionic twin pregnancies, due to quite high risk of perinatal mortality and morbidity in monochorionic monoamniotic (MM) twins. Counting the number of yolk sacs is believed to be good indicator of amnionicity in the early first trimester, as the number of yolk sacs is alleged to be equal to amnionicity order in both MM and monochorionic diamniotic (MD) twin pregnancies. However, the accuracy of the relationship between number of yolk sacs and amnionicity has recently been called into question in MD twin pregnancies. To the best of our knowledge, no previous reports have shown two yolk sacs in MM twin pregnancies. We report 2 cases of MM twins with two yolk sacs on first trimester ultrasonography, and confirmed monoamnionicity showing umbilical cord entanglement and postnatal placental examination. Pregnant courses of both cases were uneventful, and elective Cesarean sections were performed at 33 + 2 and 34 + 4 weeks of gestation, respectively. All four babies showed good growth without any complications by 2 years old and 4 months old in each. Amnionicity of both cases were also confirmed MM twin placenta after postnatal gross examinations. In conclusion, two yolk sacs in cases of MM twin pregnancy may not be a rare finding and can be expected to show equivalent outcomes to MM twin pregnancy with a single yolk sac. Detection of two yolk sacs on ultrasound examination in monochorionic twin pregnancy does not rule out monoamnionicity. The possibility of monoamnionicity must still be suspected when two yolk sacs are detected early in the first trimester ultrasound examination for monochorionic twin pregnancies.