Indirect pump: unique presentation of a monochorionic–triamniotic triplet gestation complicated by TRAP sequence and successfully managed with radiofrequency ablation of the acardiac fetus

Abstract

Twin reversed arterial perfusion (TRAP) sequence is a rare complication of multiple gestations. Only a few cases of TRAP sequence in monochorionic triplets have been reported. Here we report a case of TRAP sequence in a monochorionic–triamniotic triplet gestation treated with radiofrequency ablation of the acardiac fetus. The response to the radiofrequency ablation procedure and subsequent examination of the placenta support the hypothesis of an ‘indirect’ pump triplet.

CASE REPORT

A 22-year-old woman, gravida 1 para 0, was found to have a triplet pregnancy at an initial 21-week comprehensive ultrasound examination. Fetal demise with hydropic changes in one of the fetuses was initially suspected. A subsequent ultrasound examination by a maternal–fetal medicine specialist confirmed a monochorionic–triamniotic triplet gestation with absence of cardiac activity in one of the triplets. Additionally, reversed flow in the umbilical cord of this fetus was demonstrated on Doppler ultrasound examination. These findings were consistent with a monochorionic–triamniotic gestation complicated by twin reversed arterial perfusion (TRAP) sequence.

On evaluation at our center at 22+5 weeks’ gestation, Doppler examination confirmed reversed flow through the single umbilical artery of the acardiac fetus, Triplet A. Generalized soft-tissue edema was seen and the amniotic fluid volume was normal (Figure 1). Triplet B, the suspected pump fetus (estimated fetal weight, 377 g), showed an increased amniotic fluid volume with a maximal vertical pocket of 11cm. Slight cardiomegaly (cardiac index, 0.56) and mild tricuspid regurgitation were noted. The placental cord insertion was found in proximity to the placental cord insertion of the acardiac fetus (1.5 cm). Triplet C (estimated fetal weight, 327 g) revealed only elevated amniotic fluid volume with a maximal vertical pocket of 9 cm. The placental cord insertion of Triplet C was marginal. The patient and her family elected to defer an immediate decision regarding management of the pregnancy.

Figure 1.

Ultrasound image of acardiac triplet (Triplet A) in a monochorionic–triamniotic gestation complicated by twin reversed arterial perfusion sequence.

Evaluation 5 days later revealed a further increase in the amniotic fluid volume in Triplets B and C (maximal vertical pockets of 12.5 and 11.5 cm, respectively). The cardiomegaly in Triplet B was also noted to have progressed slightly (cardiac index, 0.59). At this point the patient decided to undergo radiofrequency ablation of the acardiac fetus.

Ultrasound-guided radiofrequency ablation of blood flow to the acardiac triplet was performed the next day. The procedure was technically challenging, as the amniotic sac of the target acardiac fetus (Triplet A) was posterior to the sac of the pump fetus (Triplet B). A 17-gauge RITA™ SDE needle (AngioDynamics, Queensbury, NY, USA) was inserted through the amniotic sac of Triplet B, with perforation of the intertwin membrane, in order to reach the target acardiac fetus. The procedure was uncomplicated, with complete cessation of blood flow in the acardiac fetus at the end of the procedure, confirmed on Doppler ultrasound examination. Additionally, amnioreduction of 650mL using an 18-gauge needle was undertaken from the sac of the pump fetus.

The day following the procedure, a return of minimal flow to the acardiac fetus was noted in addition to an increase in the middle cerebral artery peak systolic velocity (MCA-PSV) of Triplet B (multiples of the median (MoM), 1.75) and Triplet C (MoM, 1.96). These findings suggested failure of the ablation procedure. A repeat ablation procedure was planned for the following day. However, a preoperative ultrasound assessment demonstrated complete absence of flow to the acardiac fetus so the repeat procedure was canceled.

Magnetic resonance examination with diffusion-weighted imaging was performed 2 days later and was normal in the surviving fetuses. A further follow-up ultrasound examination 2 weeks later demonstrated normalization of the MCA-PSV of both surviving fetuses. Six weeks later, normalization of the amniotic fluid in Triplet C was seen. Gradual resolution of the cardiomegaly and tricuspid regurgitation in Triplet B was also noted.

At 31 weeks’ gestation the patient presented with rupture of membranes. After a latency period of 5 days, labor ensued and a primary low transverse Cesarean section (secondary to breech position of the presenting fetus) was performed. The patient delivered the two surviving infants and the macerated ex-acardiac Triplet A. Triplet B weighed 1515 g and had Apgar scores of 8 and 8 at 1 and 5 min, respectively, with a hemoglobin level of 17.1 g/dL. Triplet C weighed 1275 g and had Apgar scores of 7 and 9 at 1 and 5 min, respectively, and a hemoglobin level of 20.1 g/dL. The babies required ventilator support for 2 days, and they spent 3 weeks in the neonatal intensive care unit. Brain ultrasound examinations were performed on days 10 and 35 after birth in both Triplets B and C; no abnormalities were found.

DISCUSSION

TRAP sequence is a rare condition that occurs in about 1% of monochorionic pregnancies and in 1 in 35 000 deliveries¹. Monochorionic triplet pregnancies occur at a rate of approximately 1 in 45 500 deliveries². Since 1% of these will have TRAP sequence, the simultaneous occurrence of these two entities (monochorionic triplet pregnancy with TRAP) would represent a rare event in obstetrics (approximately 1 in 4.5 million pregnancies). Without treatment, the mortality can be as high as 55%³. This condition is characterized by the presence of a twin with an absent or non-functioning heart, known as the acardiac twin, and the presence of a twin that provides perfusion, known as the pump twin. It is even more unusual to see this condition complicating a triplet gestation, with only a few case reports having been described^4–6. With monochorionic triplets, the pump–acardiac complex may present differently as one acardiac and two pump fetuses, one pump and two acardiac fetuses or one acardiac, one pump and one unaffected fetus.

Here we describe a monochorionic–triamniotic triplet gestation complicated by TRAP sequence, successfully treated with radiofrequency ablation. We hypothesize the existence of an ‘indirect pump’ fetus that contributes to the perfusion of the acardiac twin indirectly, through diversion of its blood supply to the pump fetus (Figure 2).

Figure 2.

Schematic representation of ‘indirect pump’ hypothesis in a monochorionic–triamniotic triplet gestation complicated by twin reversed arterial perfusion sequence.

During the initial assessment of the case, both Triplets B and C revealed polyhydramnios, and in both fetuses resolution of the polyhydramnios was observed after successful cessation of blood flow to the acardiac fetus. This finding supports a high cardiac output state in both Triplets B and C due to the shunting of blood from the pump fetus to the acardiac fetus and from the indirect pump fetus to the direct pump fetus. In addition, the initial failure of complete ablation observed on postoperative day one appeared to result in an elevation of the MCA-PSV in both Triplets B and C.

Examination of the vascular architecture of the placenta also supports our hypothesis of the existence of an indirect pump. We demonstrated the existence of four large vascular anastomoses between Triplets B and C (Figure 3). Three of these anastomoses were arteriovenous (with directional flow from Triplet C to Triplet B) and one was venovenous in nature. Additionally, no direct vascular connections between the acardiac fetus and Triplet C were identified. Furthermore, the close proximity of the cord insertions between the acardiac fetus and Triplet B, and the relative distance between the acardiac fetus and Triplet C, support the concept of a direct pump (in close proximity to the acardiac twin providing direct reversed perfusion) and an indirect pump (contributing blood volume to the ‘intermediate fetus’, Triplet B).

Figure 3.

Photograph of placental vascular surface in a monochorionic–triamniotic triplet gestation complicated by twin reversed arterial perfusion sequence, showing distance between cord insertions of Triplets A and B (circle) and vascular anastomoses between Triplets B and C (arrows).

We propose therefore that in cases of monochorionic multiple gestations complicated by TRAP sequence, monitoring the hemodynamic status of all fetuses is required in order to anticipate any complicated vascular interactions.