Ultrasound in Obstetrics & Gynecology vol:44 issue:6 pages:722-4
Monochorionic (MC) twin pregnancies are at increased risk of adverse outcome because of the vascular anastomoses that connect the two fetal circulations. MC monoamniotic (MA) twins are at an even higher risk due to the almost universal cord entanglement and possible compression, which can cause an acute transfusion imbalance between the twins. Chorionicity and amnionicity should be determined during the first trimester ultrasound examination scan to identify the high-risk MC and MA twin pregnancy for which a fortnightly follow-up may improve outcome. Although this can be readily achieved by assessing and counting the membranes that separate the twin, some pitfalls may occur. In this case series, we present two monozygotic twin pairs with an intermediate type of mono- dichorionic and mono-diamniotic twin pregnancy. The first was picked-up during the first trimester scan and the second during the second trimester scan.