Monochorionic twins are at risk for complications due to the presence of placental vascular anastomoses, including twin-twin transfusion syndrome, twin anemia-polycythemia sequence, selective fetal growth restriction, and twin reversed arterial perfusion sequence. While ultrasound is the primary modality to screen for the development of these complications, MRI plays an important role in assessing monochorionic twin pregnancies for the development of other complications, such as neurologic injury. In this article, the authors review the ultrasound imaging findings associated with monochorionic twin complications, management options, and the role for MRI in these pregnancies.

BACKGROUND: The optimal approach and therapy method for the acardiac twin with a reverse arterial perfusion sequence has not yet been established. The aim of this study was to determine the clinical practice patterns among international fetal therapy units in their management of these cases.
METHODS: A survey was sent to fetal centers across the world via email between December 2020 and December 2021.
RESULTS: Responses were obtained from 77% contacted centers. The most frequent ultrasound variables used in the evaluation of twin reverse arterial perfusion sequence include echocardiographic assessment of the pump twin and umbilical artery Doppler waveforms in the acardiac and pump twins, in 90% and 80% of the centers, respectively. Most centers in Europe and Latin America propose an in utero intervention in all cases. Most centers in Europe and Latin America prefer interstitial laser ablation, whereas radiofrequency ablation (RFA) is preferred in North America. The earliest gestational age for an intervention is on mean 13 weeks in Europe, which is earlier than the other geographic areas (p = 0.001).
CONCLUSIONS: Most centers agreed that antenatal evaluation should include echocardiography along with the UA Doppler waveform measurements, and the most frequently used interventions were interstitial laser ablation or RFA at a median between 14 and 26 weeks.

BACKGROUND: Over the past years, intrafetal laser (IFL) therapy has been increasingly used in the management of various prenatal conditions. The aim of our research was to clarify the effectiveness and safety of this technique.
METHODS: A systematic review of the literature was carried out using MEDLINE/PubMed over a period of 20 years (2001-2021).
RESULTS: A total of forty-one articles were selected in the literature search, including 194 cases of twin reversed arterial perfusion (TRAP) sequence, 56 cases of bronchopulmonary sequestrations (BPSs), 5 cases of placental chorioangiomas (PCA), 11 cases of sacrococcygeal teratoma (SCT), and 103 cases of embryo reduction (ER) managed using IFL. In TRAP sequence, perfusion of the acardiac twin was successfully disrupted in all cases. However, preterm premature rupture of membranes (P-PROMs) occurred in 6 out of 79 pregnancies (7.5%), and preterm birth (PTB) occurred in 36 out of 122 pregnancies (29.5%). In BPS, IFL was successfully performed in all cases with no significant fetal-maternal complications. The rates of P-PROM and PTB were, respectively, 3.2% and 12.5%. All PCA IFL-treated cases resulted in successful pregnancy outcomes; no cases of P-PROM were reported, but the rate of PTB reached a peak of 60% due to complications such as severe fetal growth restriction and fetal Doppler abnormalities. In SCT cases, complete cessation of blood flow was achieved in 4 patients (36.4%); P-PROM occurred in 2 cases (18.2%), whereas the rate of PTB was 87.5%. In ER, no intraoperative or major maternal complications were described in the literature. Rates of miscarriage and PTB differed between initial trichorionic triamniotic and dichorionic triamniotic triplet pregnancies.
CONCLUSIONS: Our analysis suggests that IFL is a safe and feasible technique for the management of different fetal conditions. However, the overall risk of PTB, and its related morbidity and mortality, ranges from 12.5% in BPS to 87.5% in SCT IFL-treated cases. This information could aid in decision-making during prenatal counseling. However, final perinatal outcome depends on the severity of the disease itself.

BACKGROUND: Twin reversed arterial perfusion (TRAP) sequence is an extremely rare congenital anomaly in monochorionic (MC) twins. The condition is characterized by a malformed fetus (acardiac twin) without cardiac activities being perfused by a structurally normal one (pump twin) via an artery-to-artery anastomosis in a reverse direction.
METHODS: We described the first case of TRAP to receive laser surgery in Vietnam. The 26-wk pregnancy was originally misdiagnosed in another hospital as MC twins with single intrauterine fetal death. Following admission to our center, the diagnosis was amended to a 26-wk TRAP sequence stage IIb. The acardiac twin was 7.5 cm at the longest length, the ratio of the weight of the acardiac twin to the weight of the pump twin was more than 90%, the pump twin showed fetal distress with absent diastolic flow in umbilical artery of pump twin, and the peak systolic velocity in the middle cerebral artery = 1.6 MoM. We performed emergency laser photocoagulation of the acardiac twin\'s umbilical cord. After surgery, we successfully maintained the pregnancy for 8 wk and ended it electively by cesarean section at 34 wk of gestation due to rupture of membranes.
CONCLUSIONS: TRAP should be appropriately diagnosed and treated early to avoid complications of the pump twin. Fetoscopic laser photocoagulation is a new and effective treatment for this condition.

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UNASSIGNED: Twin reversed arterial perfusion (TRAP) sequence occurs when there is one non-viable twin without cardiac structures and a viable pump twin that perfuses the acardiac mass. This study aims to investigate the management and immediate neonatal outcomes for monochorionic multiple pregnancies complicated by TRAP referred to the NSW Fetal Therapy Centre (NSW FTC).
UNASSIGNED: Retrospective cohort study of multiple pregnancies referred to NSW FTC between April 2006 and April 2014, reviewing data for cases of TRAP sequence (n = 19, including two triplet cases) compared to a timeframe matched sample of uncomplicated monochorionic diamniotic (MCDA) twin pregnancies managed in the unit (n = 45).
UNASSIGNED: Primary management of the 19 TRAP cases was expectant management in 10 (53%), radiofrequency ablation (RFA) in 6 (32%), and bipolar cord coagulation, amniodrainage and termination of pregnancy in 1 case each. 1 of 6 RFA cases had pump twin demise <1 week post-procedure. Average gestation at birth (35.1 ± 5.0 vs. 35.0 ± 2.8 weeks) and mean birthweight (2157 ± 1019 g vs. 2245 ± 537 g) were similar between TRAP pump fetuses and uncomplicated MCDA cases. Pump twin survival was 81% (twins only) compared to 98% for uncomplicated MCDA twins (P = 0.02), and in 5 of 19 (26%) TRAP pregnancies the pump fetus had a congenital anomaly.
UNASSIGNED: Mean gestational age at birth and mean birthweight were similar for both TRAP and uncomplicated MCDA pregnancies. TRAP cases, however, had higher perinatal mortality, and high rates of congenital anomaly. The overall neonatal outcome at NSW FTC for TRAP cases is similar to reported international outcomes.

Multifetal pregnancy reduction is a technique used to reduce the fetal number to mitigate the risks of adverse outcomes associated with multiple gestations. Monochorionic diamniotic twin pregnancies are subject to unique complications, contributing to adverse pregnancy outcomes. Thus, patients have an option to electively reduce 1 fetus to improve outcomes.
This study aimed to compare outcomes of elective reduction of monochorionic diamniotic twins by radiofrequency ablation to planned ongoing monochorionic diamniotic twins.
We performed a retrospective review of 315 monochorionic diamniotic twin gestations that underwent first-trimester ultrasound within 1 institution. Planned electively reduced twins were compared with ongoing monochorionic diamniotic twins. All reductions were performed via radiofrequency ablation of the cord insertion site into the fetal abdomen. The primary outcome was preterm birth at <36 weeks\' gestation. Secondary outcomes included gestational age at delivery; preterm birth at less than 37-, 34-, 32-, and 28-weeks\' gestation; unintended loss; and adverse perinatal outcomes.
Among 315 monochorionic diamniotic pregnancies, 14 (4.4%) underwent elective multifetal pregnancy reduction, and 301 (95.6%) were planned ongoing twins. The mean gestational age of radiofrequency ablation in the elective multifetal pregnancy reduction group was 15.1±0.68 weeks. Patients who underwent elective multifetal pregnancy reduction had significantly higher maternal age (P<.01) and were more likely to be Asian (P<.01). Moreover, they were more likely to have undergone in vitro fertilization (P=.03) and chorionic villus sampling (P<.01). There was a significantly higher rate of term deliveries in the elective radiofrequency ablation group compared with ongoing twins (gestational age, 38 weeks [interquartile range, 36.1-39.1] vs 35.9 weeks [interquartile range, 34.0-36.9]; P<.01). Patients with ongoing pregnancies had a trend of increased rate of preterm birth at <36 weeks\' gestation (odds ratio, 3.4; 95% confidence interval, 1.0-12.0; P=.06), a significantly increased risk of preterm birth at <37 weeks\' gestation (odds ratio, 8.0; 95% confidence interval, 2.4-26.4; P<.01), and no difference at less than 34-, 32-, or 28- weeks\' gestation. All patients who underwent elective radiofrequency ablation had successful pregnancies with no pregnancy losses or terminations. Of ongoing gestations, 36 required procedures, including 16 (5.3%) medically indicated radiofrequency ablation, 14 (4.6%) laser ablation, and 6 (1.9%) amnioreductions. Furthermore, 22 patients (7.3%) with planned ongoing twins had total pregnancy loss at <24 weeks\' gestation. Notably, 12 patients (4.0%) had unintended loss of 1 fetus before 24 weeks\' gestation in the ongoing pregnancy cohort, and 12 patients (4.0%) had unintended loss of both fetuses before 24 weeks\' gestation. Moreover, 5 patients (1.7%) in the ongoing pregnancy group had intrauterine fetal demise at >24 weeks\' gestation and 10 patients (3.3%) electively terminated both fetuses. There was no significant difference in loss rates between the 2 groups.
In this study of monochorionic diamniotic twins, patients who elected to undergo multifetal pregnancy reduction had significantly lower rates of preterm birth at <37 weeks and a lower trend of preterm birth at <36 weeks\' gestation without an increased risk of pregnancy loss. Median gestational age at delivery was significantly higher in the elective multifetal pregnancy reduction group (38 weeks) than in the ongoing pregnancy group (35.9 weeks). Further research is needed to clarify if multifetal pregnancy reduction improves long-term outcomes.

BACKGROUND: Preterm prelabor rupture of membranes (PPROM) is a common complication after fetal surgeries. The aim of this study was to assess risk factors for and outcomes after PPROM following cord occlusion (CO) in monochorionic diamniotic (MCDA) pregnancies.
METHODS: This was a retrospective cohort study of 188 consecutive MCDA pregnancies treated by bipolar or laser CO, either primarily because of discordant malformation (dMF) or severe selective fetal growth restriction (sFGR), or secondarily when complete bichorionization was not possible in case of twin-to-twin transfusion syndrome (TTTS) or sFGR. Intentional septostomy was performed when needed. The procedure-related PPROM was defined as rupture of membranes <32 weeks\' gestation (PROM <32 weeks). Selected pre-, intra-, and early postoperative variables were analyzed by univariate and binomial logistic regression to determine they are correlated to PROM <32 weeks after CO.
RESULTS: Between 2006 and 2017, 188 cases underwent CO. Diagnosis was TTTS in 28.2% (n = 53), severe sFGR in 49.5% (n = 93), and dMF in 22.3% (n = 42). PROM <32 weeks occurred in 21.3% (n = 40), resulting in worse perinatal outcomes, as preterm birth <32 weeks occurred in 80.7% (vs. 8.3%, p = 0.000), procedure-to-delivery interval was 47.5 days (vs. 125, p = 0.000), gestational age (GA) at birth 30.0 weeks (vs. 37.7 weeks, p = 0.000), and survival 65.0% (vs. 91.1%, p = 0.000). In univariate analysis, indication, anterior placenta, cervical length, GA at surgery, operation time, amniodistention and drainage fluid volumes, chorioamniotic membrane separation, and septostomy were selected as relevant factors to be included in the regression model. In a multivariate analysis, TTTS was the only factor associated to PROM <32 weeks (OR 3.5 CI 95% 1.5-7.9).
CONCLUSIONS: PROM <32 weeks after CO increases the risk of preterm delivery. In this cohort, the membrane rupture was more likely when CO was done in the context of TTTS.

Acardiac twin or twin reversed arterial perfusion (TRAP) sequence is a rare medical complication of Monozygotic twins. Taiwanese Obstetricians usually treat TRAP sequence conservatively. Occasionally, repeated amnio-reduction is performed to decompress the polyhydramnios caused by the TRAP sequence, even though there was no correction of the pathophysiologic mechanism. Radiofrequency ablation is a minimally invasive, percutaneous technique that can effectively obliterate blood supply to an acardiac twin to preserve and protect the pump twin. This recent technique has never been used before for the treatment of the TRAP sequence in Taiwan. This article reported the first-hand experience of acardiac twin management with RFA in Taipei Chang Gung Memorial Hospital.

To report the outcome of monochorionic twins with twin reversed arterial perfusion (TRAP) sequence following interstitial laser therapy in the first trimester.
This was a retrospective cohort study of all consecutive cases of TRAP that underwent interstitial laser therapy at ≤ 14 + 3 weeks\' gestation between January 2014 and April 2016. Interstitial laser treatment was performed under ultrasound guidance using a 400-nm Nd:YAG laser fiber. Hospital records were reviewed to ascertain perinatal survival and morbidity.
Twelve monochorionic twin pregnancies underwent interstitial laser treatment of the umbilical artery of the acardiac fetus, at a median gestational age of 13 + 5 (interquartile range (IQR), 13 + 4 to 14 + 0) weeks. In all cases, one treatment was sufficient to achieve complete interruption of the perfusion of the acardiac twin. There were no procedure-related complications during or within 48 h after the procedure. In one (8.3%) case, intrauterine death of the pump twin occurred 2 weeks after the intervention. All other cases (91.7%) resulted in a live birth at a median gestational age of 39 + 6 (IQR, 37 + 1 to 41 + 2) weeks and with a median birth weight of 3370 (IQR, 2980-3480) g. No neonatal mortality or serious morbidity occurred.
Our results support the use of interstitial laser therapy in the first trimester of pregnancy complicated by TRAP sequence, showing a live birth rate of 92%. The results of a randomized controlled trial, evaluating early vs late intervention in pregnancy with TRAP sequence, are awaited. © 2019 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.