Monochorionic triamniotic (MCTA) triplet pregnancy complicated by TRAP sequence: successful management with ultrasound-guided radiofrequency ablation and favourable outcome

Abstract

We present a case of a 30-year-old G3P2L1 with a spontaneously conceived monochorionic triamniotic (MCTA) triplet pregnancy complicated by a Twin Reversed Arterial Perfusion (TRAP) sequence in one fetus. Early ultrasound at 10 weeks 4 days showed MCTA triplets with one hydropic fetus with alobar holoprosencephaly. A review scan at 12 weeks 6 days gestation showed that this fetus with holoprosencephaly had no heart. Colour Doppler showed a single artery in the acardiac fetus, suggestive of twin reverse arterial perfusion (TRAP sequence). Ultrasound-guided radiofrequency ablation (RFA) was successfully performed at 19 weeks and 2 days. The patient required cerclage at 23 weeks due to cervical shortening. She was delivered by Caesarean section at 33 weeks and 5 days in view of fetal growth restriction and abnormal Dopplers in twin 2. Both babies, weighing 1625g and 1460 g, were discharged well after 7 & 11 days of NICU stay. This case highlights the importance of early diagnosis, ultrasound surveillance, timely intervention, and multidisciplinary care in the management of this extremely rare triplet pregnancy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40748-026-00267-6.

Introduction

Monochorionic triamniotic (MCTA) triplet pregnancies are rare with a reported incidence of 2.6-4% of triplet pregnancies, which themselves are uncommon [1, 2]. The presence of Twin Reversed Arterial Perfusion (TRAP) sequence in these rare pregnancies adds to the clinical complexity. The TRAP sequence, characterised by the presence of an acardiac fetus, results from abnormal vascular anastomoses in monochorionic placentas. This condition poses significant risks to the pump fetus(es), including high-output cardiac failure, polyhydramnios, and preterm birth. There are only a few cases of MCTA triplets with TRAP reported in the literature with variable management and outcomes [1, 3–14]. This case report details the successful management of a rare MCTA triplet pregnancy complicated by TRAP sequence.

Case Presentation

We present a case of a 30-year-old G3P2L1 lady with a spontaneously conceived monochorionic triamniotic (MCTA) triplet pregnancy. This was a nonconsanguineous marriage with no significant family history. Her first pregnancy resulted in preterm lower segment caesarean section (LSCS) at 36 weeks in view of uncontrolled hypertension. A baby girl weighing 1,900 g at birth was born, requiring 3–4 days of Neonatal Intensive Care Unit (NICU) stay. This child is alive and healthy. In her second pregnancy, she had a spontaneous preterm delivery at 28 weeks, but there was an intrapartum stillbirth, and she delivered the stillborn male baby vaginally. There was no postnatal evaluation. Both these pregnancies were managed elsewhere. She presented to us in her current pregnancy at 10 weeks. She was diagnosed with chronic hypertension and was started on labetalol and low-dose aspirin at booking.

Clinical course and management

A transabdominal and transvaginal ultrasound was performed at 10 weeks 4 days on Voluson E10 scanner (GE Healthcare, Milwaukee, WI, USA) equipped with a convex 4– 8 MHz abdominal and 6– 12 MHz vaginal transducer. It showed a single chorion with three amniotic sacs containing three embryos. Monochorionicity was confirmed by the thin intertwin membranes as described in the literature. Two embryos were growing appropriately for gestation, whereas the third embryo showed findings suspicious of lobar holoprosencephaly and had a thick nuchal translucency with generalised subcutaneous oedema. Cardiac structures were not visualised for this embryo. A review scan at 12 weeks 6 days gestation showed that this fetus with holoprosencephaly had no heart, and colour Doppler showed a single artery in the acardiac fetus, suggestive of twin reverse arterial perfusion (TRAP sequence) (Fig. 1). The other two fetuses did not show any abnormality and were growing appropriately.

Fig. 1.

Ultrasound images at 12 weeks and 4 days gestation: 3D image showing monochorionic triplets, fetus labelled 3 is the smallest [A] 2D image showing holoprosencephaly [B] and nuchal edema [C]. Colour Doppler showing retrograde flow through a single vessel going into the acardiac fetus [D]

The patient was counselled for selective fetal reduction of the TRAP fetus by ultrasound-guided interstitial laser or radiofrequency ablation (RFA). She opted for expectant management and presented for the next review at 18 weeks and 6 days: the acardiac fetus had, but the other two fetuses did not show any signs of cardiac overload. There were no signs of twin-twin transfusion syndrome (TTTS) or selective fetal growth restriction (sFGR); cervical length was normal at 32 mm with the internal os closed and no funnelling. The couple was again counselled in detail regarding the risk of hydrops and cardiac failure due to the growing TRAP fetus, along with the risk of prematurity with triplet pregnancy, especially since she had a history of preterm births. Since the size of the acardiac fetus had grown (Fig. 2), we chose to do the selective reduction of the TRAP fetus by radiofrequency ablation (RFA) rather than interstitial laser. The 20% risk of co-twin demise, PPROM and miscarriage associated with the procedure was discussed. We also counselled the couple regarding the possibility of brain injury and neurological sequelae with any intervention in monochorionic pregnancies.

Fig. 2.

[A] Pre-procedure transabdominal colour Doppler ultrasound at 18 weeks and 6 days showing reversed arterial flow in the acardiac fetus. [B] Post RFA follow-up scan at 22 weeks and 5 days showing no colour flow in the TRAP fetus

The couple agreed for the procedure, which was performed at 19 weeks under local anaesthesia. The pre-procedure volume of the acardiac fetus was 282.7 ml. Ultrasound-guided RFA of the feeding vessel going to the TRAP fetus was done using a 17 F ablator (video). A single cycle of ablation (100 degrees, 3 min and 1 min cooling off) led to a complete cessation of blood flow in the feeding vessel. The procedure was uneventful.

Subsequent follow-up scans showed appropriately growing MCDA twins with normal Dopplers. Cervical screening at 23 weeks showed a short cervical length of 15.2 mm with funnelling, and a McDonald’s cerclage was performed. She was followed up with two weekly ultrasound scans as per protocol for monochorionic pregnancies. Maternal surveillance was done for development of superimposed preeclampsia. She developed proteinuria at 29 weeks and required increase in the dose of Labetalol due to rising BP records.

On ultrasound surveillance, twin 2 developed selective fetal growth restriction (sFGR) at 31 weeks with an estimated fetal weight (EFW) on 8th centile and high resistance in the umbilical artery. Weekly ultrasound follow-up was done. This fetus developed absent end-diastolic flow (AEDF) in the umbilical artery at 33 weeks and 2 days. Antenatal steroids were given, and the fetuses were delivered after 48 h by caesarean section.

Neonatal outcome

Two male babies with birth weights of 1625 g and 1460 g were delivered with APGAR scores of 5,8 and 6,9, at 1 and 5 min respectively. Baby 1 had respiratory distress after birth, for which he was admitted to the NICU and started on nasal CPAP. The baby also had episodes of apneas, for which he was started on Caffeine Citrate. The baby was taken off CPAP on Day 3 of life and discharged on Day 7 of life. Baby 2 also had respiratory distress, for which he required CPAP for 48 h. On day 3 of life, the baby was taken off CPAP successfully. The baby stayed in the NICU for 11 days because of very low birth weight. The second baby was discharged on D11 of life. Both babies are now 9 months old and are thriving well. Milestones are normal for age.

Discussion

TRAP sequence is a complication unique to monochorionic pregnancies with a reported incidence of 1% [15, 16]. It is characterised by a single arterio-arterial and veno-venous anastomosis leading to reversed arterial perfusion in the acardiac twin, which receives deoxygenated blood from the healthy ‘pump’ co-twin (Fig. 2). Most published literature is from monochorionic diamniotic (MCDA) twin pregnancies with one acardiac fetus. Management options are expectant management or fetal intervention to stop the abnormal blood supply by interstitial laser, radiofrequency ablation or bipolar cord coagulation. Expectant management can be opted for if the TRAP fetus is small and there are no signs of cardiac compromise in the pump fetus. However, there is increasing evidence that survival rates are higher in pregnancies where prenatal intervention was performed as compared to pregnancies where expectant management was opted for (82.6% vs. 64.5%, p = 0.0001) [15]. In fact, the current question in the management of TRAP is the timing of intervention. The results of a randomised control trial, the Twin Reversed Arterial Perfusion Intervention STudy (TRAPIST), comparing outcomes from early intervention (at 12–14 weeks) versus late intervention (16–18 weeks) in MCDA twins are awaited (NCT02621645).

Given that the incidence of monochorionic triplets itself is low, the occurrence of MCTA triplets with one acardiac fetus is even rarer. We have presented all published cases reported till date in Table 1 [1, 3–14, 17]. Out of a total of 23 included cases, 14 (61%) had twin survival, 3 women had a single survival (13%) and 6 (26%) women lost both fetuses. The variation in management and outcomes highlights the lack of uniformity in the management of this rare combination. Since intervention improves outcomes in MCDA twins with TRAP, we postulated that intervention should be the preferred management in MC triplets, as triplet pregnancy itself predisposes to the high incidence of prematurity.

Table 1.

Clinical characteristics and outcomes of Monochorionic Triamniotic (MCTA) Triplets with TRAP sequence reported in literature

Reference	Patients	GA at Diagnosis (weeks)	Active Intervention	Additional Anomaly	Additional Complications	GA at Delivery (weeks)	Twin Survival	Single Survival	No Survivor
Takahashi Y [3] (2001)	1	16	RFA	No	PPROM	29 (CS); BW: 1167 g, 1237 g	Both	-	-
Sepulveda W [4] (2009)	1	10	None	No	IUFD of both viable fetuses At 12 weeks	-	-	-	Yes
Argoti PS [5] (2013)	1	17	RFA at 17 + 4 weeks	No	No	34 (CS); BW: 2380 g, 2450 g	Both	-	-
López-Pérez R [6] (2015)	1	20	None	No	No	32 (CS)	Both	-	-
Sugibayashi S [7] (2016)	1	13 + 5	RFA at 16 + 2 weeks	No	No	36 + 5 (CS)	Both	-	-
Pan P [8] (2017)	1	16	FLS at 16 weeks	No	No	36 (CS); BW: 2500 g, 2650 g	Both	-	-
Kobori S [9] (2019)	1	20	RFA at 20 weeks	No	No	35 (CS); BW: 2200 g, 2350 g	Both	-	-
Takano M [10](2019)	1	16	FLS at 16 + 1 weeks	Severe sFGR Type II	sFGR type II, PROM post-procedure, preterm labor	28 + 4 (CS)	Both	-	-
Yildirim E [11] (2019)	1	12	No	No	Spontaneous miscarriage at 14 weeks	-	-	-	Yes
Seshadri R [12] (2020)	2	17 (case 1), 20 (case 2)	Intrafetal laser	No	Preterm labor, NND in 1 case	35 (case 1), 33 (case 2) both CS	Case 1: both; Case 2: one survivor, one NND	Yes (case 2)	-
Mon A [13](2021)	2	Case 1: 20, Case 2: 21	No (both cases)	No	Case 1: termination at 20 wks, Case 2: preterm labor at 21 wks	-	-	-	Yes (both cases)
Sileo FG [1] (2023)	8	12–26	7/8 active: 3 interstitial laser, 3 RFA, 1 cord occlusion	3/8 had additional anomalies	1/8 with additional complications	Median 33 weeks (range 27–37)	4/8 (50%)	2/8 (25%)	2/8 (25%)
Zhao Y [14] (2024)	1	22	RFA at 22 weeks	No	No	33 (CS); BW: 2450 g, 2300 g	Both	-	-
Present case (2025)	1	19	RFA at 19 weeks	No	FGR, maternal preeclampsia	33 + 4 (CS); BW: 1625 g, 1460 g	Both	-	-

In the largest reported series on MCTA triplet pregnancies complicated by TRAP, Sileo et al. demonstrated that active intervention significantly improves survival, with an overall twin survival rate of 50% following selective fetal reduction via RFA, laser ablation, or cord occlusion [1]. Similar outcomes have been reported in smaller series and case reports, including the successful use of RFA [5, 8, 9].

Our case aligns with this growing body of evidence. The decision to perform RFA at 19 weeks was guided by the interval growth of the acardiac fetus, with the known risks of cardiac compromise in the pump twin eventually leading to hydrops, fetal demise and polyhydramnios. The procedure was technically successful, with cessation of perfusion in the acardiac fetus and no immediate procedure-related complications. The subsequent development of cervical shortening necessitating cervical cerclage highlights the multifactorial risks inherent to high-order monochorionic pregnancies and the importance of regular ultrasound surveillance in these high-risk pregnancies.

Monochorionic pregnancies are at increased risk of developing fetal growth restriction and preterm birth. Women with multiple pregnancies are also at increased risk of developing gestational hypertension and preeclampsia. All these complications occurred in our patient and were managed as per standard guidelines [16]. Serial ultrasound surveillance for growth abnormalities and Doppler changes remains essential in monochorionic twins for the timely recognition of these complications.

Finally, the favourable neonatal outcomes in both pump twins, with normal neurodevelopmental milestones at 7 months of age, affirm the efficacy of timely intervention and multidisciplinary care in optimizing outcomes in such complex pregnancies. This reinforces the importance of early diagnosis, detailed counselling, and close follow-up in managing MCTA pregnancies complicated by TRAP.

Conclusion

This case underscores the importance of early diagnosis, serial monitoring, and timely intervention in managing the TRAP sequence in an MCTA triplet pregnancy. Radiofrequency ablation, coupled with vigilant monitoring and management of cervical insufficiency, contributed to the favourable neonatal outcomes.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

CS, VA, NG and JS wrote the main manuscript. SG & MN prepared the figures. All authors reviewed the manuscript.

Funding

The authors did not receive any funding for this work.

Data availability

Not applicable.

Declarations

Ethics approval and consent to participate

The manuscript has been prepared in accordance with the Helsinki Declaration and only anonymized data has been used. Consent has been obtained from the patient for publication of this case report. Ethical clearance was obtained from the Institutional Review Board of Madhukar Rainbow Children’s Hospital, New Delhi.

Consent for publication

The patient has given consent for publication of this anonymised case report.

Competing interests

The authors declare no competing interests.