Despite advances in diagnostic approaches, fetal anemia of unknown etiology continues to be observed in rare cases. This study aimed to assess the incidence of unexplained fetal anemia and to evaluate the associated perinatal outcomes.We conducted an observational retrospective cohort study of all fetuses that underwent fetal blood sampling (FBS) due to an MCA-PSV>1.5 MoM at a tertiary center between 2007 and 2024. Fetuses were included if they had moderate or severe anemia defined as a hemoglobin (Hgb) deviation of more than 20g/L below a gestational age adjusted mean, with a negative anemia workup. Prenatal and postnatal outcomes were obtained.Among 376 fetuses that underwent fetal blood sampling for anemia, 361 (96%) had an identified cause, while 15 (4%) had moderate to severe anemia of unknown etiology. Seven fetuses presented with non-immune hydrops and eight with other major structural anomalies not typically associated with anemia. Eleven (73%) of the 15 fetuses with unexplained anemia had thrombocytopenia, with platelets below 100000/µL in 8 cases and below 50000/µL in 6 cases. Seven cases (47%) resulted in perinatal death. Rare causes of anemia were elucidated in only 5 cases (33%) postnatally despite extensive investigations.Unexplained fetal anemia is uncommon and is associated with poor neonatal outcomes warranting close pre- and postnatal surveillance.

OBJECTIVE:Characterize neuroimaging findings in foetuses with anaemia and identify associated risk factors. METHODS:Retrospective cohort study of pregnancies with foetal anaemia (defined as haemoglobin > 2 standard deviations below the gestational age mean) confirmed by foetal blood sampling (FBS) and treated with intrauterine transfusion (IUT) at a tertiary centre between 2011 and 2024. Prenatal and/or early postnatal neuroimaging findings and perinatal outcomes were reviewed. Multivariable logistic regression was used to identify factors associated with brain injury on neuroimaging. RESULTS:Of 100 foetuses with foetal anaemia that underwent neuroimaging, 93 met the eligibility criteria. Brain injuries were identified in 48 foetuses (52%). Injuries included intracranial haemorrhage (48%), ischaemia (21%), combined injury (6%), and non-specific injuries (25%). Imaging was performed prenatally (n = 36), postnatally (n = 36), or both (n = 21). Male sex was independently associated with brain injury (adjusted OR 5.04, 95% CI 1.64-15.52; p = 0.005). Anaemia severity, hydrops, cardiac dysfunction, and gestational age at diagnosis were not associated with brain injury. Immediate postnatal outcomes did not differ between the groups. CONCLUSION:In a clinically selected cohort of foetuses with anaemia who underwent neuroimaging after IUT, brain injuries were frequent and heterogeneous. These findings support the need for prospective studies with standardized imaging and longitudinal follow-up to define true risk and identify subgroups most likely to benefit from surveillance.

Objective To document the natural history and complications of second- and third-trimester non-nuchal lymphatic malformations (LM) and identify predictors of these complications. Methods We conducted a single-centre retrospective review of fetuses diagnosed with LMs between January 2015 and January 2024. Lesion size was quantified using the lymphatic malformation volume ratio (LVR): LVR = 0.523 x width x length x height (cm(3)) / head circumference (cm). Outcomes and LVR growth trends were analyzed using Student's t-test and a linear mixed-effects model. Results Eighteen cases were included (10 cervical, 8 axillary). Uncomplicated cervical LMs grew at 0.3 cm(2)/week (p < 0.001). Intralesional bleeding (n = 3) was associated with LVR > 11 cm(2) and significantly higher growth rates (2.6 vs. 0.3 cm(2)/week; p = 0.005). All cases with LVR > 5 cm(2) required subsequent tracheostomy after birth. Axillary LMs grew at 0.21 cm(2)/week. One case with bleeding had LVR 4.4 cm(2). Median LVR was significantly lower in vaginal deliveries compared with complicated births (2.0 vs. 7.3 cm(2); p = 0.03). All LVR > 4 cm(2) led to delivery complications. Conclusion Higher LVR predicts haemorrhage and airway intervention in cervical LMs, and delivery complications in axillary LMs. These exploratory observations warrant confirmation in larger prospective cohorts.

INTRODUCTION:Severe brain injury has been reported following fetoscopic laser ablation (FLA) for twin-to-twin transfusion syndrome (TTTS), but imaging patterns and temporal evolution remain poorly defined. This study aimed to characterize the progression of severe brain injury after FLA. METHODS:We conducted a retrospective case series of TTTS pregnancies with severe brain injury identified after FLA at the Ontario Fetal Center (June 2023-March 2025). FLA was performed for Quintero stage ≥ II and selected stage I cases. Severe abnormalities were defined as severe intraventricular haemorrhage or destructive lesions. Serial ultrasound and fetal MRI were reviewed and categorized as early (< 4 weeks) or late (≥ 4 weeks) post-FLA. RESULTS:Fifteen fetuses from 14 pregnancies were identified. Mean gestational age at FLA was 19.7 ± 3.2 weeks; 66.7% were stage III-IV and 60% were donor twins. Early imaging (n = 8) most commonly showed periventricular haemorrhagic infarction (62.5%) and cerebellar haemorrhage (25.0%). Late imaging (n = 13) predominantly demonstrated cerebral volume loss (76.9%), often involving the parietal lobes, with polymicrogyria (38.5%) and Wallerian degeneration (30.8%). Findings remained unchanged after 4 weeks. CONCLUSION:Brain injury after FLA evolves from acute haemorrhagic/ischaemic insults to irreversible destructive changes. These preliminary findings suggest a consistent pattern of injury that warrants further prospective study.

Objective: This study compared insertion difficulties, shunt failure, reintervention rates, maternal adverse events, and neonatal outcomes among different shunt types used in fetal hydrothorax. Method: A retrospective multicenter cohort study (2012-2022) was conducted across 12 international centers. The primary outcome was the occurrence of complications, classified as insertion difficulties and shunt failure (dislocation, occlusion, or unexplained shunt failure). Secondary outcomes included reintervention rates, maternal complications, and neonatal survival. Results: Among 349 cases, 345 were included in the analysis of the outcome measures. Rodeck shunts had significantly fewer complications (19.5%) compared to Somatex (38.3%, OR 2.53, p = 0.016) and Harrison shunts (50.0%, OR 3.82, p < 0.001). Somatex shunts had the highest rate of incorrect positioning (16%), while dislocation was most frequent with Harrison shunts (31.1%). Reintervention rates were lowest for Rodeck (12.1%) and highest for Harrison (32.2%). Maternal body mass index, fetal hydrops, laterality and year of shunt placement did not significantly influence complication rates. No significant differences in live birth rates or gestational age at delivery were observed. Conclusions: The Rodeck shunt was associated with fewer insertion difficulties, better shunt performance and lower reintervention rates. There was no difference in perinatal survival among the three shunt types.

OBJECTIVE:The primary objective of this study was to assess whether incorporating paraspinal myofascial flaps and/or an acellular dermal matrix (ADM) patch during open fetal surgery for open spina bifida (OSB) impacts the need for CSF diversion by 1 year of age. A secondary objective was to determine whether these interventions affect pregnancy outcomes. METHODS:The authors retrospectively reviewed all fetuses undergoing open fetal OSB repair at their center from June 2017 through April 2024. Factors associated with CSF diversion surgery at 1 year of age were collected and included lesion type, lesion level, lateral ventricle size, and gestational age (GA) at surgery. Pregnancy outcomes assessed were GA at delivery and the incidence of prelabor premature rupture of membranes (PPROM). Univariate and multivariate logistic regression were used to evaluate factors associated with postnatal CSF diversion at 12 months. Chi-square tests and 1-way ANOVA were used for group comparisons. RESULTS:Of 57 fetuses treated with surgery, 4 were excluded (due to failed repair, early delivery, neonatal death, or loss to follow-up), leaving 53 neonates for analysis. In univariate analysis, the use of myofascial flaps (OR 0.14, 95% CI 0.01-0.81) and ADM patches (OR 0.26, 95% CI 0.05-0.95) was associated with reduced odds of CSF diversion. In multivariate analysis, ADM patch use remained significantly associated with a reduced need for diversion (aOR 0.24, 95% CI 0.01-0.70), while myofascial flap use showed a trend toward benefit (aOR 0.34, 95% CI 0.01-1.03). PPROM rates were not significantly different between the groups: 32.1% without either intervention, 33.3% with myofascial flap alone, 27.3% with ADM alone, and 16.7% with both (p = 0.85). The mean GA at delivery was also similar: 35.1 ± 1.8 weeks (no ADM patch/flap), 35.4 ± 1.5 weeks (myofascial flap), 35.0 ± 3.2 weeks (ADM patch), and 35.3 ± 2.5 weeks (both) (p = 0.98). CONCLUSIONS:Use of an ADM patch during fetal OSB repair was associated with a lower likelihood of requiring CSF diversion at 1 year. Paraspinal myofascial flaps showed a favorable trend toward similar benefit. Neither intervention increased the risk of PPROM or preterm birth, supporting their safety as surgical adjuncts.

Key Points We thank the letter authors for their interest in our work. We agree that this report fits well into a framework for the development of simulation in order to teach fetoscopic laser management of twin to twin transfusion syndrome. Current studies are underway at our center in order to validate the utility of the simulator in teaching this important surgical skill.

OBJECTIVE:To determine pre-procedure maternal, pregnancy and fetal factors associated with survival until 6 months of age and evaluate temporal trends in survival outcomes over a 25-year period following fetoscopic laser ablation (FLA) of placental anastomoses in monochorionic twin pregnancies with twin-twin transfusion syndrome (TTTS). DESIGN:Retrospective observational study. SETTINGS:A tertiary care fetal centre in Canada. POPULATION OR SAMPLE:One thousand and five patients undergoing TTTS between 1998 and 2023. METHODS:Patient demographics, pregnancy, procedural and outcome details were collected. Predictors for single and dual survival were identified using multivariable logistic regression. Temporal trends in survival outcomes across the study period were also examined. MAIN OUTCOME MEASURES:Fetal/neonatal survival at 6 months and predictors for single and dual survival. RESULTS:Of 915 included fetoscopies, 597 pregnancies (65.2%) achieved dual survival, 217 (23.9%) had a single survivor, and 101 (11%) resulted in dual demise. Survival rates improved significantly over the 25-year study period for both single and dual survival (p = 0.03 and p = 0.0004, respectively). Three significant pre-procedural predictors of dual demise versus one or two survivors were: cervical length ≤ 15 mm (adjusted odds ratio [AOR] 6.1, 95% CI 2.7-14.1), earlier gestational age (GA) at intervention (AOR 1.2 per earlier week, 95% CI 1.1-1.3), and abnormal donor umbilical artery Doppler flow (AOR 5.1, 95% CI 1.7-15.6). A prediction calculator using this model achieved an area under the curve of 0.65. CONCLUSION:Short cervical length (≤ 15 mm), presence of abnormal donor umbilical artery Doppler waveform, and early GA at time of intervention are significant predictors of fetal/neonatal survival at 6 months following FLA in TTTS and thus, are valuable parameters to consider for pre-procedural counselling.

INTRODUCTION:Twin-twin transfusion syndrome (TTTS) may complicate triplet pregnancies with a monochorionic component; however, data on foetoscopic laser ablation (FLA) in this setting remain limited. This study evaluated perinatal outcomes in TTTS-affected triplet pregnancies with at least one monochorionic placenta treated with FLA and compared these with monochorionic diamniotic (MC/DA) twin pregnancies. METHODS:We retrospectively reviewed 42 triplet pregnancies complicated by TTTS treated with FLA. Of these, 25 were dichorionic triamniotic (DC/TA, 59.5%) and 17 were monochorionic triamniotic (MC/TA, 40.5%). Antenatal, procedural, and neonatal outcomes were compared with those of 1,072 MC/DA twin pregnancies treated with FLA at the same centre. Categorical and continuous variables were compared using the chi-square/Fisher's exact test and Mann-Whitney U test, respectively, with p < 0.05 considered statistically significant. Proportions are presented with 95% confidence intervals, and subgroup analyses were considered exploratory. RESULT:Quintero stage distribution did not differ significantly between cohorts, and gestational age (GA) at FLA was 20.3 weeks (IQR 18.7-22.3) in triplets and 20.4 weeks (IQR 18.4-23.1) in twins. Procedural complications in triplets were infrequent and did not differ significantly from twins. PPROM rates and laser time did not differ significantly. Survival of unaffected triplet was 88.1%. Among TTTS-affected pairs within triplets, dual neonatal survival was 61.9%, with at least one survivor in 85.7%. Dual survival was more frequent in MC/TA (70.6%) than in DC/TA (56.0%) triplets. Survival outcomes were not statistically different from those of MC/DA twins (dual: 70.1%, at least one 91.6%). The median GA at delivery was 31.8 weeks in triplets and 32.3 weeks in twins. CONCLUSIONS:Triplet pregnancies with TTTS treated with FLA showed no statistically significant differences in antenatal and neonatal outcomes to MC/DA twins, with high survival rates and low complication rates reported.

OBJECTIVE:Describe prenatal imaging characteristics, perinatal and postnatal outcomes in fetuses with isolated macrocystic congenital pulmonary airway malformations (CPAM) undergoing thoracoamniotic shunting (TAS) and expectant management. METHODS:Retrospective cohort study of 123 fetuses with isolated macrocystic CPAM managed at the Ontario Fetal Center (1998-2024). Prenatal ultrasound features, perinatal outcomes, and postnatal surgical data were described for fetuses undergoing TAS and expectantly managed. Predictors of mortality were assessed in the TAS group. RESULTS:TAS was performed in 30/123 (24%) of cases. Shunted fetuses had higher CPAM volume ratio (CVR) (1.5 vs. 0.5), larger cyst diameter (3.4 vs. 1.0 cm), mediastinal shift (58% vs. 7%), and hydrops (16.7% vs. 0%). Lesion size decreased after TAS in 80% of cases; however, survival was lower (85% vs. 100), and preterm delivery was more frequent (24% vs. 7%). Among shunted cases, CVR > 2 or persistent hydrops were associated with perinatal mortality. Neonatal respiratory support was required more often following TAS (86% vs. 25%). Most infants underwent postnatal resection, occurring earlier after TAS (0.1 vs. 7.0 months). CONCLUSIONS:Macrocystic CPAM represents a high-risk subtype of congenital lung malformations, with a substantial proportion requiring fetal intervention, neonatal respiratory support, and postnatal surgical resection. These findings support tertiary surveillance and delivery.

Introduction: The aim of the study was to analyze the evolution, indications, and outcomes of cephalocentesis over a 38-year period at two tertiary fetal medicine centers. METHODS:A retrospective review of 70 cephalocentesis procedures (1985-2023) was conducted at Mount Sinai Hospital, Toronto, and the National Maternity Hospital, Dublin. Cases were divided into pre-2002 (n = 37) and 2002-onward (n = 33) cohorts in order to evaluate practice evolution. RESULTS:Mean gestational age at diagnosis was 32.7 ± 5.4 weeks with severe hydrocephalus in 95.7% (67/70) and hydranencephaly in 4.3% (3/70) of cases. Pre-2002, 94.6% (35/37) of procedures were performed intrapartum; 2002 onward, this shifted to 66.7% (22/33) pre-labor planned procedures with 84.8% (28/33) using a transabdominal approach. Concurrent fetal analgesia and potassium chloride (KCl) to achieve fetal asystole was introduced in 2002. Vaginal delivery was achieved in 95.7% (67/70) of cases. Perinatal mortality (excluding KCl cases) was 91.8% (45/49). All four survivors (5.8%) demonstrated neurodevelopmental impairment. CONCLUSION:Cephalocentesis has evolved from an intrapartum intervention to a planned procedure with standardized protocols. Our findings support reserving this procedure for cases where there is no expectation of postnatal survival, with the primary purpose of facilitating vaginal delivery when caesarean section could unnecessarily increase maternal morbidity. .

Mirror syndrome, previously referred to as Ballantyne's syndrome, is a rare obstetric disorder characterized by maternal edema in association with fetal hydrops and placental edema. This report concerns the case of a 35-year-old multiparous woman who developed mirror syndrome secondary to fetal supraventricular tachycardia complicated by hydrops and intrauterine fetal demise. Her pregnancy was further complicated by hypereactio luteinalis with ovarian torsion requiring surgical detorsion. The case highlights the challenges of managing maternal and fetal hydrps, and its rare association with hypereactio luteinalis.

Fetal therapy has advanced with novel pharmacological approaches to address congenital tumors and malformations, including cardiac rhabdomyomas and lymphatic malformations (LMs). Cardiac rhabdomyomas, often associated with tuberous sclerosis complex (TSC), can lead to significant morbidity due to arrhythmias, left or right ventricular outflow tract obstruction and heart failure, particularly in neonates. LMs, resulting from abnormal development of the lymphatic system, can cause considerable morbidity, including airway obstruction, disfigurement, recurrent infections, bleeding into cysts, and impaired function of affected organs, depending on location. Recent therapies involving mammalian target rapamycin (mTOR) inhibitors, such as everolimus and sirolimus, offer promising interventions for these conditions. As mTOR inhibitors target dysregulated cell growth and angiogenesis, they can effectively reduce the size of both cardiac rhabdomyomas and LMs in-utero. Clinical studies in the pediatric population have shown that mTOR inhibitors promote regression of cardiac rhabdomyomas, leading to improved cardiac function, and similarly reduce the size of lymphatic malformations, thereby decreasing the need for surgical or interventional procedures. Sirolimus has also shown efficacy in treating complex LMs and is increasingly being used as a first line agent alone as well as in conjunction with other treatment modalities like surgery and sclerotherapy. Despite potential side effects, including gastrointestinal discomfort and an increased risk of infection, the risk-benefit ratio should be carefully evaluated on an individual patient basis. This review examines current evidence supporting the use of mTOR inhibitors in fetal therapy, highlighting their ability to mitigate postnatal complications and improve long-term outcomes. Further research is needed to optimize dosing protocols and assess the long-term safety of these therapies in the fetal population.

OBJECTIVE:To develop and validate a novel virtual reality (VR) simulation system for training fetoscopic laser placental photocoagulation in twin-to-twin transfusion syndrome (TTTS). METHODS:A VR-based simulator incorporating Meta Quest headsets and custom-designed hardware was developed. The system features realistic anatomical modeling, integrated performance metrics, and progressive training modules. Validation involved 31 participants (11 experienced fetal therapy specialists, 10 fetal therapy fellows, and 10 other maternal-fetal medicine specialists) who evaluated the simulator across five domains using a standardized questionnaire. RESULTS:The simulator demonstrated excellent internal consistency (Cronbach's α = 0.92) with strong positive validation across all measured aspects. Training effectiveness received the highest endorsement (87%, 95% CI: 83%-91%), followed by user engagement (85%, 95% CI: 81%-89%). Experienced specialists rated environmental realism significantly higher (4.8 ± 0.3, p = 0.002), while fellows provided the strongest endorsement for training effectiveness (4.8 ± 0.3, p = 0.004). CONCLUSIONS:This VR simulator represents a significant advancement in TTTS surgical education, offering comprehensive training capabilities without requiring practice on actual patients. Initial testing demonstrates feasibility for both local and remote teaching applications, with potential advantages in cost, portability, and educational capabilities compared to traditional physical simulators.

INTRODUCTION:Both a low and an increased body mass index (BMI) are risk factors for surgical complications. It is less clear whether they also affect the outcomes of fetoscopic procedures. In this manuscript, we aimed to assess the effect of maternal BMI on operative and pregnancy outcomes following fetoscopic laser ablation of placental anastomoses for twin-twin transfusion syndrome (TTTS). METHODS:We retrospectively reviewed all patients with twin pregnancies complicated by TTTS treated with fetoscopic laser surgery at the Ontario Fetal Centre, Toronto, over a 24-year period. Demographic and procedural data as well as pregnancy and delivery outcomes were prospectively collected as part of our quality control program. Patients were divided into 6 groups for BMI at the time of surgery: BMI <20, 20-24.9, 25-29.9, 30-34.9, 35-39.9, and ≥40 kg/m2. Collected variables included demographics, operative characteristics, operative complications, obstetric complications, twin anemia-polycythemia sequence, TTTS recurrence, intrauterine (fetal) death, gestational age at delivery, and survival. Outcomes of all groups were compared to the "normal weight" reference cohort (BMI: 20-24.9 kg/m2). RESULTS:Of 1,012 patients in our database, 859 were twin pregnancies treated with laser for TTTS. Pregnancy outcomes were available for 515. Of all patients, 47% were categorized as normal weight, 3% were underweight, 25% were obese, and 5% had a BMI of >40 kg/m2. Patients with a higher BMI had higher parity (p = 0.0001), longer cervical length (p = 0.008), and a significantly higher TTTS stage (p = 0.0003) at the time of surgery. There were no significant differences between groups in terms of surgical or anesthetic characteristics or perinatal complications. CONCLUSION:BMI does not significantly affect operative or perinatal outcomes in patients undergoing fetoscopic laser ablation for severe TTTS, despite being at a higher stage at diagnosis.

The Society for Maternal-Fetal Medicine recently released updated clinical guidelines on the ultrasound surveillance and clinical management of monochorionic twin pregnancies. The North American Fetal Therapy Network has supported but has not endorsed these guidelines. In this document, we suggest an enhanced ultrasound surveillance strategy for timely detection of twin-twin transfusion syndrome and twin anemia polycythemia sequence in monochorionic pregnancies. We provide specific recommendations that depart from the Society for Maternal-Fetal Medicine guidelines. The rationale for these recommendations includes a conceptual framework for complications of monochorionic twins, a review of Doppler studies in the diagnosis of twin-twin transfusion syndrome and a review of the pathophysiology, clinical management, and prognosis of twin anemia polycythemia sequence.

OBJECTIVE:The primary aim was to assess the feasibility of robotic OSB repair in a simulation training model, documenting the learning curve and ensuring quality control among surgeons. DESIGN:The learning curve was assessed using the cumulative summation test (LC-CUSUM). Following LC-CUSUM, six additional experiments were performed for competency-cumulative summation (C-CUSUM) analysis to ensure ongoing quality control. SETTING:The simulator was created through 3D printing and hand sculpting, simulating a partially exteriorised uterus for laparotomy-assisted laparoscopic OSB surgery. It included a silicone uterus, placenta and foetal manikin with a simulated OSB lesion, replicating the lesion sac, paraspinal muscles and neural placode. POPULATION:Four surgeons participated: an expert Maternal Fetal Medicine consultant, a neurosurgical consultant, a Maternal Fetal Medicine fellow and a neurosurgical resident. METHODS:The surgical procedure included eight steps: uterine access, working space creation, lesion exposition, junctional zone dissection, skin mobilisation, dural patch application, closure of myofascial flaps and closure of skin. Success was defined by precise restoration (suture interval < 3 mm), foetal repair time ≤ 120 min and a GEARS score > 21/30. MAIN OUTCOMES:Learning curve and competency were documented via LC-CUSUM and C-CUSUM. RESULTS:Competence was achieved after 15-21 procedures, with novices reaching competency within this range. Participants maintained high performance in subsequent quality-controlled procedures. CONCLUSION:Robotic-assisted foetal OSB surgery in a high-fidelity simulation is feasible, showing promising outcomes for a large animal model and clinical translation.

INTRODUCTION:Limited data exist regarding the effect of pre-operative risk factors on fetal survival for patients undergoing fetoscopic laser photocoagulation (FLP) for twin-twin transfusion syndrome (TTTS). The primary objective of this study was to determine the pre-operative variables predictive of single and dual fetal survival at birth for subjects treated with laser for TTTS. The secondary objective was to determine the combined effect of multiple risk factors on single and dual fetal survival at birth. METHODS:This was a prospective cohort study of TTTS pregnancies treated with FLP between 2001 and 2023. Cases were identified through the Monochorionic Twin Pregnancy Registry of the North American Fetal Therapy Network. Several pre-operative risk factors were evaluated, including maternal body mass index, gestational age at laser, fetal growth restriction (FGR), cervical length, placental location, and TTTS stage. Higher order multiples, fetal anomalies, karyotypic abnormalities, and cases with missing data were excluded. Risk factors influencing survival were assessed with uni- and multi-variate regression analyses. The predicted probability of single/dual survival based on these risk factors was assessed with multiple logistic regression analysis. RESULTS:Of 2,728 FLP cases, 1,066 met inclusion criteria. Dual survival is reduced in stage 3 and 4 disease compared to stage 1 and 2 (OR 0.75: 0.58, 0.98; p = 0.032) with the lowest survival in all stages occurring with FGR. An anterior placenta (aOR 0.58: 0.37, 0.91; p = 0.017) and FGR <10th percentile (aOR 0.57: 0.35, 0.92; p = 0.02) were independent predictors of reduced survival. With regression modeling, sequential addition of any pre-operative risk factor progressively reduces survival of at least one or both twins. CONCLUSIONS:In this large registry, anterior placental location and FGR were most predictive of reduced survival for both twins. As the number of pre-operative risk factors increases for a given TTTS case, there is a progressive reduction in survival probability and these reported probability rates may be useful in counseling patients.