Partial monochorionic and monoamniotic twin pregnancies: a report of two cases

Abstract

Monochorionic (MC) twin pregnancies are at increased CASE REPORTSThe first case was a spontaneous twin pregnancy of a 25-year-old woman, gravida 2 para 1, referred at 12 weeks' gestation for chorionicity determination. Ultrasound showed only two thin separating amniotic membranes at the lower part of the intertwin septum and one thick chorionic membrane in conjunction with two thin amniotic membranes at the upper part (Figure 1), resulting in the diagnosis of a partial monochorionic (MC) twin pregnancy. The pregnancy was followed up as an MC twin pregnancy with fortnightly ultrasound examinations. The pregnancy was uneventful and the patient delivered two healthy girls of 2535g and 2595g at 36 weeks' gestation. Postnatal macroscopic evaluation of the intertwin membrane confirmed our diagnosis, showing both an opaque and a translucent part of the septum (Figure 2). Placental injection documented the presence of vascular anastomoses across the MC part of the septum. Pathological examination of the intertwin septum confirmed both the amnion-amnion and amnion-chorion-amnion attachment, indicating a partial MC and dichorionic (DC) septum (Figure 3), as was diagnosed at the first-trimester scan. DNA fingerprinting using fibroblasts cultured from the umbilical cords confirmed monozygosity.The second case was a twin pregnancy conceived by intracytoplasmatic sperm injection in a 26-year-old woman, gravida 3 para 1. The first-trimester scan showed two thin amniotic membranes (Figure 4, inset), typical in an MC diamniotic (DA) twin pregnancy, and a fortnightly follow-up scan was recommended. Re-evaluation at 20 weeks' gestation showed that the intertwin septum no longer separated the two twins, but that both were on the same side of the septum and their cords were entangled. The initial diagnosis of a diamniotic pregnancy was therefore changed to a partial monoamniotic (MA) pregnancy. From 28 weeks onwards, the woman was managed as an inpatient to provide fetal surveillance and treatment for fetal lung maturation, as is usual for MA pairs1 . An emergency Cesarean section was performed at 31 weeks' gestation because of preterm prelabor rupture of membranes and the clinical suspicion of placental abruption. Two healthy boys of 1630g and 1440g were delivered. Postpartum macroscopic evaluation confirmed the presence of cord entanglement and revealed a partial DA intertwin septum between the cord insertions (Figure 4). Examination of the injected placenta documented the presence of vascular anastomoses, as typically seen in MC placentas.

‘False’ lambda sign in monochorionic twin pregnancy

“…A study published recently (although undertaken during [2004][2005][2006] found that 19% of pathological monochorionic twins were misclassified on ultrasound, which is concerning, although the study included all ultrasound examinations performed before 20 weeks' gestation 9 . That study, in conjunction with our own case and that reported by Galjaard et al 1…”

“…We read with interest the recent report by Galjaard et al of a case of partial monochorionic, partial dichorionic monozygotic twins 1 . Recently, we managed a related case that highlights the same clinical message.…”

Pseudomonoamniotic Pregnancy: Case Report and Review of Etiologic Considerations

“…The occurrence of partial monochorionic or partial monoamniotic twinning has also been documented, though these terms refer to incomplete septum formation secondary to the timing of zygotic cleavage. 3 Increased use of sonographic imaging for antenatal surveillance of monochorionic gestations has led to better recognition of pseudo-monoamniotic twins. However, the etiology of spontaneous rupture of the dividing membrane remains unknown due to the scarcity of this population.…”

Histopathological examination of the placenta in twin pregnancies

“…Subsequent placental examination showed features in different areas in keeping with both dichorionic and monochorionic placentation. These placentas showing mixed monochorionic and dichorionic features have been described as showing hybrid chorionicity or as monodichorionic . Because of these mixed patterns, the entire dividing membrane and vascular equator should be grossly evaluated in all twins.…”

“…Occasionally, the intertwin membrane in a MCDA pregnancy may become disrupted during pregnancy or during delivery, and potential remnants of this membrane should be sought. Recently, there has been a case report of a partial monoamniotic cavity where the amnion was incompletely divided . In evaluating cord entanglement in MCMA twins, certain simple procedures can be followed.…”