Ultrasonographic signs of twin–twin transfusion syndrome in a monoamniotic twin pregnancy

Abstract

Twin–twin transfusion syndrome (TTTS) is a complication of monochorionic pregnancies usually described in diamniotic but also in monoamniotic pregnancies1, 2. The syndrome is defined sonographically by the presence of polyhydramnios in one twin's sac (recipient twin) and oligohydramnios in the sac of the other twin (donor twin)3, 4. Other sonographic parameters include discordant bladder sizes, hydrops and abnormal Doppler studies of the arterial or venous circulation5. We report the case of a 24-year-old woman, gravida 2 para 1, who was referred to our department at 16 weeks of gestation with polyhydramnios in a monoamniotic monochorionic twin pregnancy. Ultrasound examination revealed discordant biometries, cord diameters and bladder sizes. Both cords were inserted on the placental margin and close to one another. Color Doppler and three-dimensional power Doppler showed large superficial anastomoses (Figure 1). An HDI 5000 (ATL, Courtaboeuf, France) ultrasound machine equipped with a 8–5 MHz broadband array was used. Doppler waveforms (umbilical artery and ductus venosus) were normal in Twin 1 (recipient) and indicated high-impedance flow in Twin 2 (donor). Follow-up at 19 weeks showed increased amniotic fluid index (32 cm) and reversed flow in the umbilical artery of Twin 2. Spontaneous resolution of polyhydramnios occurred at 26–28 weeks but biometries and bladder sizes remained discordant although the fetuses exhibited good activity and no effusion. At 29 + 4 weeks we observed biventricular cardiac hypertrophy in Twin 1 associated with tricuspid regurgitation and pulmonary artery hypertension (right ventricular pressure increased to 110 mmHg). A Cesarean section was performed at 30 weeks. Twin 1 weighed 1640 g with a 17 g/dL hemoglobin rate and he died postnatally at 22 h because of cardiac failure related to myocardial hypertrophy. Twin 2 weighed 1270 g with a 13 g/dL hemoglobin rate and he survived. Pathological examination of the placenta confirmed the monochorionic monoamniotic pregnancy with numerous vascular anastomoses (Figure 2). Three-dimensional power Doppler imaging demonstrating anastomosis (arrow) and the positions of the donor (D) and recipient (R) cords. Postnatal examination of the placenta demonstrating the discordant sizes of the donor (D) and recipient (R) cords. In this case we observed the main ultrasonographic signs of TTTS (polyhydramnios, discordance in bladder sizes and cord diameters and Doppler waveforms, arteriovenous placental anastomoses) and the evolution was consistent with an unbalanced blood flow (myocardial overload and polyglobulia (hemoglobin = 17 g/dL) in the recipient twin). In monoamniotic twin pregnancies the classical ultrasonographic sign of discordant amniotic sacs with deviated interfetal membrane can obviously not be observed. Nevertheless, polyhydramnios and discordant bladder sizes are currently considered to be sufficient evidence for the presence of unbalanced blood flow4. Some authors have attempted to explain why such a complication is rarely described in the literature. Monoamniotic and diamniotic-monochorionic placentas have different anastomotic patterns6, 7. The higher incidence of arterio-arterial anastomoses in monoamniotic twin pregnancies leads to more balanced anastomotic patterns and predicts that TTTS will occur approximately five times less often. We suggest close monitoring with fortnightly scans for all monochorionic pregnancies to detect the onset of TTTS. The first signs of TTTS based on polyhydramnios and discordant bladder sizes are easy to diagnose and warrant further investigation in a referral center to decide on the most appropriate management (observation, invasive procedures such as photocoagulation of the anastomoses, selective feticide, labor induction or Cesarean section). D. Gallot* , J.-P. Saulnier , D. Savary*, H. Laurichesse-Delmas* , D. Lemery* , * Maternal Fetal Medicine Unit, Maternité Hôtel-Dieu, CHU de Clermont-Ferrand, Boulevard Léon Malfreyt, 63003 Clermont-Ferrand cédex, France, Department of Pediatrics, Université d'Auvergne Clermont I, Hôtel-Dieu, CHU de Clermont-Ferrand, Boulevard Léon Malfreyt, 63003 Clermont-Ferrand cédex, France, JE 2447 ARDEMO, Université d'Auvergne Clermont I, Hôtel-Dieu, CHU de Clermont-Ferrand, Boulevard Léon Malfreyt, 63003 Clermont-Ferrand cédex, France