30% of spontaneously occurring twins are monozygotic, of which two-thirds are monochorionic, possessing a single placenta. A common placental mass with shared inter-twin placental circulation is key to the development and management of complications unique to monochorionic gestations. In this Consult, we review general considerations and a contemporary approach to twin-twin transfusion syndrome and twin anemia polycythemia sequence, providing management recommendations based on the available evidence. The following are Society for Maternal-Fetal Medicine recommendations: (1) we recommend routine first trimester sonographic determination of chorionicity and amnionicity (GRADE 1B); (2) we recommend that ultrasound surveillance for twin-twin transfusion syndrome begin at 16 weeks of gestation for all monochorionic-diamniotic twin pregnancies and continue at least every 2 weeks until delivery, with more frequent monitoring indicated with clinical concern (GRADE 1C); (3) we recommend that routine sonographic surveillance for twin-twin transfusion syndrome minimally include assessment of amniotic fluid volumes on both sides of the inter-twin membrane and evaluation for the presence or absence of urine-filled fetal bladders, and ideally incorporate Doppler study of the umbilical arteries (GRADE 1C); (4) we recommend fetoscopic laser surgery as the standard treatment for stage II through stage IV twin-twin transfusion syndrome presenting between 16 and 26 weeks of gestation (GRADE 1A); (5) we recommend expectant management with at least weekly fetal surveillance for asymptomatic patients continuing pregnancies complicated by stage I twin-twin transfusion syndrome, and consideration for fetoscopic laser surgery for stage I twin-twin transfusion syndrome presentations between 16 and 26 weeks of gestation complicated by additional factors such as maternal polyhydramnios-associated symptomatology (GRADE 1B); (6) we recommend an individualized approach to laser surgery for early- and late-presenting twin-twin transfusion syndrome (GRADE 1C); (7) we recommend that all patients with twin-twin transfusion syndrome qualifying for laser therapy be referred to a fetal intervention center for further evaluation, consultation, and care (Best Practice); (8) after laser therapy, we suggest weekly surveillance for 6 weeks followed by resumption of every-other-week surveillance thereafter, unless concern exists for post-laser twin-twin transfusion syndrome, post-laser twin anemia polycythemia sequence, or fetal growth restriction (GRADE 2C); (9) following the resolution of twin-twin transfusion syndrome after fetoscopic laser surgery, and without other indications for earlier delivery, we recommend delivery of dual-surviving monochorionic-diamniotic twins at 34 to 36 weeks of gestation (GRADE 1C); (10) in twin-twin transfusion syndrome pregnancies complicated by post-treatment single fetal demise, we recommend full-term delivery (39 weeks) of the surviving co-twin to avoid complications of prematurity unless indications for earlier delivery exist (GRADE 1C); (11) we recommend that fetoscopic laser surgery should not influence the mode of delivery (Best Practice); (12) we recommend that prenatal diagnosis of twin anemia polycythemia sequence minimally requires either middle cerebral artery Doppler peak systolic velocity values >1.5 multiples of the median and <1.0 multiples of the median in donor and recipient twins, respectively, or an inter-twin Δ middle cerebral artery peak systolic velocity >0.5 multiples of the median (GRADE 1C); (13) we recommend that providers consider incorporating middle cerebral artery Doppler peak systolic velocity determinations into all monochorionic twin ultrasound surveillance beginning at 16 weeks of gestation (GRADE 1C); (14) consultation with a specialized fetal care center is recommended when twin anemia polycythemia sequence progresses to a more advanced disease stage (≥ stage II) prior to 32 weeks of gestation or when concern arises for co-existing complications such as twin-twin transfusion syndrome (Best Practice).

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: Maternal laparotomy-assisted fetoscopic surgery for in-utero myelomeningocele repair has shown that a trans-amniotic membrane suture during fetoscopic port placement can reduce postsurgical complications. Fetoscopic laser photocoagulation (FLP) for complex twins is typically performed percutaneously without a transmembrane stitch. However, in scenarios without a placental-free window, maternal laparotomy may be used for recipient sac access. Here, we present the outcomes of our series of laparotomy-assisted FLP cases, including a trans-amniotic membrane suturing of the fetoscopic port.
METHODS: Retrospective series of twin-twin transfusion syndrome or twin anemia-polycythemia sequence (TAPS) cases treated at 2 fetal centers that underwent maternal laparotomy to FLP from September 2017 to January 2023. We recorded preoperative and operative characteristics, as well as pregnancy and neonatal outcomes.
RESULTS: During the study period, 9 maternal laparotomy to FLP cases were performed. Two were excluded for prior percutaneous FLP in the pregnancy. The remaining seven utilized a maternal laparotomy to trans-amniotic membrane stitch with confirmation of proper suture placement under ultrasound guidance, and all surgeries were performed with a single 10 F Check-Flo® cannula. Mean gestational age (GA) at surgery was 19.1 weeks (range 16 weeks 4 days-23 weeks 3 days), with delivery occurring at a mean GA of 35.0 weeks (range 32 weeks 0 days-37 weeks 1 day), resulting in a mean latency of 15.8 weeks, significantly longer than what is reported in the literature and our own data (mean latency for percutaneous FLP 10.2, 95% CI 9.9-10.5). Furthermore, all cases underwent iatrogenic delivery before labor onset, with the lone delivery prior to 34 weeks due to concern for post-laser TAPS.
CONCLUSIONS: This case series of laparotomy to FLP with trans-amniotic stitch, demonstrated no cases of spontaneous preterm birth and a longer-than-expected latency from surgery to delivery. Larger studies are warranted to investigate this approach.

BACKGROUND: Twin-twin transfusion syndrome (TTTS) affects 10-15% of monochorionic twin pregnancies. Without treatment, their mortality rates would be considerable. There are differences in survival rate between different therapeutic modalities. This study aims to compare the cost-effectiveness of Fetoscopic laser versus amnioreduction, septostomy, and expected management in the treatment of twin-to-twin transfusion syndrome (TTTS).
METHODS: This is a cost-effectiveness analysis of the treatment strategies in patients with TTTS. A decision tree model was used to estimate the clinical and economic outcomes with a pregnancy period time horizon. Medical direct costs were extracted in a quantitative study, and survival rates were determined as effectiveness measures based on a review. A probabilistic sensitivity analysis was used to measure the effects of uncertainty in the model parameters. The TreeAge, Excel and R software were used for analyzing data.
RESULTS: In the first phase, 75 studies were included in the review. Based on the meta-analysis, a total of 7183 women treated with Fetoscopic laser, the perinatal survival of at least one twin-based pregnancy was 69%. In the second phase, the results showed that expected management and amnioreduction have the lowest (791.6$) and highest cost (2020.8$), respectively. Based on the decision model analysis, expected management had the lowest cost ($791.67) and the highest rate in at least one survival (89%), it was used only in early stages of TTTS. Fetoscopic laser surgery, with the mean cost 871.46$ and an overall survival rate of 0.69 considered the most cost-effectiveness strategy in other stages of TTTS.
CONCLUSIONS: Our model found Fetoscopic laser surgery in all stages of TTTS to be the most cost-effective therapy for patients with TTTS. Fetoscopic laser surgery thus should be considered a reasonable treatment option for TTTS.

Background: Most previous studies evaluated outcomes of twin-twin transfusion syndrome (TTTS) without considering the coexistence of selective fetal growth restriction (sFGR). The objectives of this study were to compare twin survival and pregnancy complications after laser therapy of TTTS with and without sFGR. Methods: For this purpose, a retrospective cohort study including 98 monochorionic diamniotic twins and three dichorionic triamniotic triplets treated in a single tertiary center was conducted. Results: Overall, 46 twins had selective fetal growth restriction (26 type I, 13 type II, 7 type III). At birth, donor survival (61% vs. 91%), double survival (57% vs. 82%), and overall survival (75% vs. 88%) were significantly lower in the group with coexistent sFGR. Recipient survival (89% vs. 86%), miscarriage (7% vs. 2%), PPROM < 32 weeks (48% vs. 29%), and preterm delivery < 32 weeks (52% vs. 45%) were not significantly higher in the group with coexistent sFGR. Donor twins with sFGR type I (69% vs. 91%) and types II-III (50% vs. 91%) showed significantly lower survival than those without sFGR. Multivariate regression analysis identified sFGR and its subtypes as independent predictors of donor demise. Conclusions: the coexistence of sFGR in TTTS pregnancies was associated with poor donor outcomes and is probably the most important predictor of donor survival.

OBJECTIVE: Fetoscopic laser coagulation of placental anastomoses is usually performed for a treatment of twin-to-twin transfusion syndrome (TTTS). A common complication of fetoscopic laser coagulation for TTTS is preterm preliminary rupture of fetal membranes (PPROM) aggravating the neonatal outcome significantly. However, use of an flexible 1 mm fetoscope with an curved sheath could reduce iatrogenic damage of the amniotic membrane and improve neonatal outcomes after laser treatment. The aim of this study was to compare neonatal outcomes using this flexible fetoscope with curved sheath vs. use of a standard lens technique.
METHODS: Outcomes were retrospective analyzed after use of a standard lens fetoscope of 2 mm (sheath 6.63 mm2 or 11.27 mm2 for anterior placenta) and a flexible fetoscope of 1 mm or 1.2 mm (sheath 2.65 mm2 or 3.34 mm2) in two German centers of fetal surgery, performed during 2006-2019.
RESULTS: Neonatal outcome of 247 TTTS patients were analyzed including the rates of double and single fetal survival. The survival of at least one fetus was 97.2 % in the group with the ultrathin technique (n=154) compared to 88.3 % (n=93) in the group with the standard lens fetoscope (p=0.008). Survival of both fetuses was not different between groups (81.0 vs. 75.3 %). The procedure to delivery interval was significantly increased using the ultrathin fetoscope (89.1±35.0 d vs. 71.4±35.4 d, p=0.001) resulting in an increased gestational age at delivery by 11 days on average (231.9±28.1 d vs. 221.1±32.7 d, p=0.012).
CONCLUSIONS: Fetal survival can be significantly increased following TTTS using flexible fetoscope of 1 mm or 1.2 mm (sheath 2.65 mm2 or 3.34 mm2).

Twin-twin transfusion syndrome (TTTS) is a serious complication in monochorionic (MC) pregnancies. Fetoscopic laser surgery (FLS) is the primary treatment for advanced TTTS, but managing Quintero stage I TTTS is still controversial. We conducted an observational study evaluating the 2-year neurodevelopment of fetuses, which underwent FLS for stage I TTTS, compared with advanced TTTS and uncomplicated monochorionic diamniotic twins (MCDTs). The study included 156 children: 14 in stage I TTTS group, 28 in advanced TTTS group, and 114 in uncomplicated twin group. In stage I TTTS, 92.9% showed normal neurodevelopment, with no severe neurological impairments observed. These results were comparable with uncomplicated twins (92.1% normal neurodevelopment, P = .921, adjusted odds ratio [aOR] = 1.56, 95% confidence interval [CI] = 0.42-5.79; 1.8% severe impairment, P = .617). Advanced TTTS had a non-significant lower rate of normal neurodevelopment (89.3%, P = .710, aOR = 1.31, 95% CI = 0.12-14.87). In conclusion, FLS for stage I TTTS shows favorable long-term neurodevelopmental outcomes, similar to uncomplicated MC pregnancies.

BACKGROUND: Twin-twin transfusion syndrome (TTTS) and selective fetal growth restriction (sFGR) are common complications in monochorionic diamniotic (MCDA) pregnancies. The Diffusion-rElaxation Combined Imaging for Detailed Placental Evaluation (DECIDE) model, a placental-specific model, separates the T2 values of the fetal and maternal blood from the background tissue and estimates the fetal blood oxygen saturation. This study investigates diffusion and relaxation differences in uncomplicated MCDA pregnancies and MCDA pregnancies complicated by TTTS and sFGR in mid-pregnancy.
METHODS: This prospective monocentric cohort study included uncomplicated MCDA pregnancies and pregnancies complicated by TTTS and sFGR. We performed MRI with conventional diffusion-weighted imaging (DWI) and combined relaxometry - DWI-intravoxel incoherent motion. DECIDE analysis was used to quantify different parameters within the placenta related to the fetal, placental, and maternal compartments.
RESULTS: We included 99 pregnancies, of which 46 were uncomplicated, 12 were complicated by sFGR and 41 by TTTS. Conventional DWI did not find differences between or within cohorts. On DECIDE imaging, fetoplacental oxygen saturation was significantly lower in the smaller member of sFGR (p = 0.07) and in both members of TTTS (p = 0.01 and p = 0.004) compared to the uncomplicated pairs. Additionally, average T2 relaxation time was significantly lower in the smaller twin of the sFGR (p = 0.004) compared to the uncomplicated twins (p = 0.03).
CONCLUSIONS: Multicompartment functional MRI showed significant differences in several MRI parameters between the placenta of uncomplicated MCDA pregnancies and those complicated by sFGR and TTTS in mid-pregnancy.

Fetoscopic laser photocoagulation (FLP) is a well-established treatment for twin-twin transfusion syndrome (TTTS) between 16 and 26 weeks\' gestation. High-quality evidence and guidelines regarding the optimal clinical management of very early (prior to 16 weeks), early (between 16 and 18 weeks) and late (after 26 weeks) TTTS are lacking. The aim of this study was to construct a structured expert-based clinical consensus for the management of early and late TTTS.
A Delphi procedure was conducted among an international panel of experts. Participants were chosen based on their clinical expertise, affiliation and relevant publications. A four-round Delphi survey was conducted using an online platform and responses were collected anonymously. In the first round, a core group of experts was asked to answer open-ended questions regarding the indications, timing and modes of treatment for early and late TTTS. In the second and third rounds, participants were asked to grade each statement on a Likert scale (1, completely disagree; 5, completely agree) and to add any suggestions or modifications. At the end of each round, the median score for each statement was calculated. Statements with a median grade of 5 without suggestions for change were accepted as the consensus. Statements with a median grade of 3 or less were excluded from the Delphi process. Statements with a median grade of 4 were modified according to suggestions and reconsidered in the next round. In the last round, participants were asked to agree or disagree with the statements, and those with more than 70% agreement without suggestions for change were considered the consensus.
A total of 122 experts met the inclusion criteria and were invited to participate, of whom 53 (43.4%) agreed to take part in the study. Of those, 75.5% completed all four rounds. A consensus on the optimal management of early and late TTTS was obtained. FLP can be offered as early as 15 weeks\' gestation for selected cases, and can be considered up to 28 weeks. Between 16 and 18 weeks, management should be tailored according to Doppler findings.
A consensus-based treatment protocol for early and late TTTS was agreed upon by a panel of experts. This protocol should be modified at the discretion of the operator, according to their experience and the specific demands of each case. This should advance the quality of future studies, guide clinical practice and improve patient care. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Twin pregnancy is associated with increased perinatal mortality and morbidity, but long-term neurodevelopmental outcome remains underinvestigated. The primary objective of this study was to investigate the incidence of adverse neurodevelopment after 1 year of age in complicated monochorionic diamniotic (MCDA) twin pregnancies compared with uncomplicated twin pregnancies.
This was a prospective cohort study conducted at St George\'s University Hospital NHS Foundation Trust, London, UK. Women with a twin pregnancy culminating in at least one surviving child, aged between 12 and 60 months (corrected for prematurity) at the time of assessment, were invited to complete the relevant Ages and Stages Questionnaire® version 3 (ASQ-3) test. The two study groups were: (1) complicated MCDA twin pregnancies, including those with twin-twin transfusion syndrome, twin anemia-polycythemia sequence, selective fetal growth restriction, twin reversed arterial perfusion sequence and/or single intrauterine demise; and (2) uncomplicated MCDA and dichorionic diamniotic twin pregnancies. The primary outcome measure was an abnormal ASQ-3 score, defined as a score of more than 2 SD below the mean in any one of the five domains. Mixed-effects multivariable logistic regression analysis was performed to determine whether a complicated MCDA twin pregnancy was associated independently with an abnormal ASQ-3 score.
The study included 174 parents who completed the questionnaire for one or both twins; therefore, 327 ASQ-3 questionnaires were available for analysis. Of those, 117 (35.8%) were complicated MCDA twin pregnancies and 210 (64.2%) were controls. The overall rate of an abnormal ASQ-3 score in children born of a complicated MCDA twin pregnancy was nearly double that of those from uncomplicated twin pregnancies (14.5% vs 7.6%; P = 0.056). Children born of a complicated MCDA twin pregnancy had a significantly higher rate of impairment in the gross-motor domain compared with the control group (8.5% vs 2.9%; P = 0.031). Complicated MCDA twin pregnancies that underwent prenatal intervention had a significantly higher rate of abnormal ASQ-3 score compared with those that did not undergo prenatal intervention (28.1% vs 1.7%; P < 0.001). On multilevel logistic regression analysis, complicated MCDA twin pregnancy was an independent predictor of abnormal ASQ-3 score (adjusted odds ratio, 3.28 (95% CI, 3.27-3.29); P < 0.001).
This study demonstrates that survivors of complicated MCDA twin pregnancies have a higher rate of adverse neurodevelopmental outcome, independently of prematurity. Long-term neurodevelopmental follow-up in these pregnancies can ensure timely and optimal management of those affected. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.