Antenatal factors at diagnosis that predict outcome in twin-twin transfusion syndrome

Controlled amnioreduction for twin-to-twin transfusion syndrome

Background:

Twin-to-twin transfusion syndrome (TTTS) is a severe condition causing preterm delivery, fetal death, and neurodevelopmental disorders. This study presents a data-based controlled amnioreduction (AR) protocol composed of sequential amniodrainage in treatment of TTTS.

Methods:

A total of 18 procedures were performed in 11 TTTS pregnancies at 17 to 34 weeks of gestation. The amniotic pressure was measured along with sequential removal of the amniotic fluid, 500 mL each step. The umbilical artery systolic/diastolic (S/D) ratio for each twin was measured pre- and post-AR. Long-term neurodevelopmental outcomes of all TTTS survivors were evaluated from parental answers to a phone survey.

Results:

The amniotic pressure decreased exponentially with the increased volume of removed amniotic fluid until a plateau was obtained. Changes of the S/D ratio between pre- and post-AR procedure did not reveal a clear tendency. The survival rate was 86.4% although 91% of all twins were at Quintero stage III. Long-term neurodevelopment outcomes in the 19 surviving twins were 68.4% optimal, 26.3% suboptimal, and 5.3% abnormal.

Conclusion:

The controlled AR procedure resulted in a relatively high rate of twin survival with favorable long-term neurodevelopment outcomes.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

Evolution of Stage 1 Twin-to-Twin Transfusion Syndrome (TTTS): Systematic Review and Meta-Analysis

Objectives: The natural history of stage 1 Twin-to-twin transfusion syndrome (TTTS) remains unclear and its optimal management is yet to be established. The main aims of this meta-analysis were to quantify the incidence of progression in stage 1 TTTS and to ascertain survival in these pregnancies.

Methods: MEDLINE, EMBASE, and The Cochrane Library were searched. Reference lists within each article were hand-searched for additional reports. The outcomes included incidence of progression and survival in stage 1 TTTS. Randomized controlled trials, cohort and case-control studies were included. Case reports, studies including three or fewer cases of stage 1 TTTS, and editorials were excluded. Proportion meta-analysis was used for analysis (Registration number: CRD42016036190).

Results: The search yielded 3,085 citations; 18 studies were included in the review (172 pregnancies to assess progression and 433 pregnancies to assess the survival). The pooled incidence of progression in stage 1 TTTS was 27% [95% CI 16–39%]. The pooled overall survival, double survival and at least one survival in the pregnancies managed expectantly were 79% [95% CI 62–92%], 70% [95% CI 54–84%] and 87% [95% CI 69–98%], respectively. In those undergoing amnioreduction, the corresponding figures were 77% [95% CI 68–85%], 67% [95% CI 57–76%] and 86% [95% CI 76–94%], respectively. The survival rates were 68% [95% CI 54–81%], 54% [95% CI 36–72%], and 81% [95% CI 69–90%], when laser surgery was performed.

Conclusions: The optimal initial management of stage 1 TTTS remains in equipoise. The ongoing randomized trial comparing immediate laser surgery versus conservative management should provide a definitive answer.

Twin-to-Twin Transfusion Syndrome: From Observational Evidence to Randomized Controlled Trials

Fetoscopic surgery is widely accepted as the preferred first-line treatment for twin-twin transfusion syndrome (TTTS). Nonetheless, the broad diffusion of this technique relies on a single multicentric-randomized trial. We hereby question this trial in a post-hoc Bayesian analysis, submitting its results to several scenarios comprising the alternative published non-randomized literature and pessimistic opinions regarding this surgery. Furthermore, we also discuss further refinements in indications, questioning potential alternatives in early stages of the disease.

What-and why-the pathologist should know about twin-to-twin transfusion syndrome

Approximately 20% of all twin pregnancies are monochorionic. Between 9% and 15% of all monochorionic twin gestations are complicated by severe chronic twin-to-twin transfusion syndrome (TTTS), characterized by a gradual shift of blood volume from the donor twin to the recipient twin through placental vascular connections [1 - 3] . The prognosis of severe, untreated chronic TTTS diagnosed in midtrimester fetuses is extremely poor, with mortality rates exceeding 70% [4] . Since publication of the results of the Eurofoetus trial in 2004, laser photocoagulation of the intertwin anastomoses has become accepted as the optimal first-line therapy for severe TTTS diagnosed before 26 weeks of gestation. While laser treatment of vascular communications was initially limited to selected fetal treatment centers, its increasingly widespread use has resulted in the exposure of more pathologists, even in less specialized institutions, to laser-treated placentas. Furthermore, the surge in laser coagulation has revived the general medical, scientific, and public interest in the placental and choriovascular findings in monochorionic twin placentas. The pathologist's understanding of the pathophysiology of TTTS and of TTTS-associated placental pathology, including the findings related to laser ablation of the anastomoses, can be of great benefit to the involved obstetric/neonatal/surgical team and, ultimately, to the patients. In this review, we summarize the current knowledge of the placental contributions to TTTS and other complications of monochorionic twinning and describe the strengths and limitations of placental examination in these settings. It is our expectation that overviews such as this may serve as a template to generate consensus guidelines for standardized and evidence-based pathologic evaluation of monochorionic twin placentas.

Placentation in Multiple Births

Outcomes of multifetal pregnancy in prenatal life are markedly affected by chorionicity. Several disease processes are found in monochorionic (MC) twins that do not occur in dichorionic (DC) twins. Improvements in prenatal outcomes will depend on reliable first trimester diagnosis of chorionicity, allowing early monitoring for complications of MC placentation. Particular structures and functions of MC twin placentas affect outcomes and can be targeted for specific treatments, especially in twin-twin transfusion. The causes of severe DC twin fetal growth discordance are clarified. In post-natal life, zygosity is a determining effect in genetic predisposition to many chronic diseases, including neoplasia. Few MC twins know that they are monozygotic (MZ). Few twin researchers realize that MZ twins may be genetically discordant. Abandonment of the word “identical” for MZ twins would assist in clarifying these issues of zygosity, concordance and discordance.

Specific complications of monochorionic twin pregnancies: twin-twin transfusion syndrome and twin reversed arterial perfusion sequence

Monochorionic twins are subjected to specific complications which originate in either imbalance or abnormality of the single placenta serving two twins. This unequal placental sharing can cause complications including twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia sequence (TAPS), selective intrauterine growth restriction or twin reversed arterial perfusion sequence (TRAP). Monochorionicity also makes the management of these specific complications as well as that of a severe malformation in one twin hazardous since the spontaneous death of one twin exposes the co-twin to a risk of exsanguination into the dead twin and its placenta. The latter is responsible for the death of the co-twin in up to 20% of the cases and in ischemic sequelae in about the same proportions in the survivors. Although the symptoms of all these complications are very different, the keystone of their management comes down to either surgical destruction of the inter-twin anastomoses on the chorionic plate when aiming at dual survival or selective and permanent occlusion of the cord of a severely affected twin aiming at protecting the normal co-twin. This can be best achieved by fetoscopic selective laser coagulation and bipolar forceps cord coagulation respectively.

Twin-twin transfusion syndrome: an ethics-based and evidence-based argument for clinical research

Aspects of twin-twin transfusion syndrome (TTTS) diagnosis, treatment alternatives, and research opportunities were considered during a consensus conference that was held by the North American Fetal Therapy Network in 2009. A 3-member scientific consensus panel gathered data from expert conference presentations, postconference communications, and comprehensive scientific literature database searches to develop recommendations for TTTS diagnosis, therapy, and research. The panel recommends retaining the Quintero staging system until a superior system has been validated appropriately. It concludes that there is normative equipoise to justify the performance of randomized clinical trials to identify the optimal treatment strategy for mild TTTS. Recommendations for the design and conduct of clinical trials and observational studies are also provided.

Twin-to-twin transfusion syndrome: a comprehensive update

Twin-to-twin transfusion syndrome (TTTS) is a serious complication in about 10% to 20% of monozygous twin gestations with an incidence of 4% to 35% in the United States. Severe TTTS is reported to occur in 5.5% to 17.5% of cases. TTTS is a progressive disease in which sudden deteriorations in clinical status can occur, leading to death of a co-twin. Up to 30% of survivors may have abnormal neurodevelopment as a result of the combination of profound antenatal insult and the complications of severe prematurity. This article presents an overview of what is known about the pathophysiology and the diagnosis of TTTS, the role of echocardiography in TTTS, treatment options available for TTTS, complications of treatment for TTTS, and short- and long-term outcomes of TTTS.

Complicated monochorionic twin pregnancies: updates in fetal diagnosis and treatment

Monochorionic (MC) twin pregnancies may develop significant complications, and twin-to-twin transfusion syndrome (TTTS) has become among the best known to obstetricians and patients alike. A significant percentage of patients referred for suspected TTTS have a different underlying pathologic condition, however, and differentiating the subcategories of MC pathophysiologic conditions may change treatment course and outcome. The key to understanding complicated MC pregnancies lies in the placental angioarchitecture and intertwin vascular communications between the fetuses.

A case of monochorionic-diamniotic twin pregnancy with polyhydramnios-polyhydramnios sequence

We present a case of monochorionic-diamniotic (MD) twin pregnancy with polyhydramnios-polyhydramnios sequence. A 20-year-old woman, gravida 1, para 0, was referred to our hospital at 31 weeks and 6 days' gestation for consultation about a high-risk pregnancy due to the presence of discordant fetal growth pattern (26% of fetal growth discordance) with polyhydramnios in MD twin pregnancy. Ultrasound examination at admission showed a maximal vertical pocket (MVP) of 11.4 cm in twin A and an MVP of 4.7 cm in twin B. At 33 weeks' gestation, the MVPs had increased to 22.2 cm and 10.2 cm, respectively. At 33 weeks and 2 days' gestation, Cesarean section was performed because of uncontrolled uterine contractions associated with polyhydramnios. Twin A was a female weighing 2,280 g, and twin B was a female weighing 1,782 g (22% growth discordance). The estimated amniotic fluid volumes of twins A and B were 5,000 and 1,000 mL, respectively.

Fetal and neonatal haematological complications in monochorionic twins

Placental vascular anastomoses are almost invariably present in monochorionic (MC) placentas. These anastomoses are the essential anatomical substrate for the development of several haematological complications in MC twins, in particular twin-to-twin transfusion syndrome (TTTS). Several forms of TTTS have been described, including chronic TTTS, acute perimortem TTTS, twin anaemia-polycythaemia sequence, acute perinatal TTTS and twin reversed arterial perfusion sequence. A significant evolution in prenatal care strategies and management options for patients with TTTS has occurred during the last decade. In chronic TTTS, endoscopic laser ablation of communicating placental vessels has led to an increase in survival rates. This review analyzes the possible pathophysiologic mechanisms involved, discusses the latest findings in diagnosis, therapy and prognosis, and focuses on fetal and neonatal haematologic complications associated with the various forms of TTTS.

Initial fetal cardiovascular profile score predicts recipient twin outcome in twin-twin transfusion syndrome

BACKGROUND

The aim of this study was to assess the relationship between cardiomyopathy and recipient twin (RT) outcome in twin-twin transfusion syndrome (TTTS).

METHODS

Fetal echocardiography and outcomes data in 62 consecutive pregnancies with TTTS were reviewed. The primary outcome was neonatal RT survival. The severity of RT cardiomyopathy at presentation was assessed by the cardiovascular profile score (CVPS). RT outcomes and odds of survival were compared between groups stratified by CVPS.

RESULTS

Overall neonatal survival for all fetuses was 61% (76 of 124). RT survival was 58% (36 of 62). Grouped by CVPS, RT survival was greater (50%) for those with CVPS > or = 9 and even higher (74%) for CVPS of 10. Among the components of the CVPS, atrioventricular valve regurgitation was associated with negative RT outcome. Other factors at presentation were not predictive of RT outcome.

CONCLUSIONS

A normal CVPS in the RT in TTTS is predictive of improved survival compared with an abnormal CVPS, even in RTs with minor deductions. Standard clinical staging did not predict outcome. Cardiac assessment by CVPS may improve clinical decision making and the timing of fetal interventions.

The value of umbilical artery Doppler velocimetry in the antenatal surveillance of uncomplicated monochorionic twin pregnancies

OBJECTIVES

To investigate the predictive value of abnormal umbilical artery Doppler findings on outcome in uncomplicated monochorionic (MC) twin pregnancies.

METHODS

Sixty-seven MC twin pregnancies, with antenatal care and delivery at the University Medical Center, Utrecht, The Netherlands, between 1999 and 2004, were studied. Pregnancies with antenatal signs of twin-to-twin transfusion syndrome were excluded. We analyzed the data according to both the last Doppler measurement of the umbilical artery before delivery and the presence of any abnormal Doppler measurement during the course of pregnancy. Risks of mortality and total neonatal morbidity were stratified according to the Doppler findings in one or both fetuses at the time of each standard ultrasound assessment in order to estimate the risk associated with an abnormal Doppler finding at or before that specific gestational age.

RESULTS

Mortality rates were similar in the normal and abnormal Doppler groups. Using both group definitions, total neonatal morbidity was higher in the abnormal Doppler group; this was significant at > 32 weeks' gestation, and was due to lower birth weight and earlier gestational age at delivery. There was no mortality at > or = 36 weeks in the abnormal Doppler group, but there were four perinatal deaths in the normal Doppler group. Gestational age at delivery was significantly lower when one or more abnormal Doppler findings had been present (median, 34 + 1 weeks vs. 36 + 3 weeks) and infants with abnormal Doppler findings weighed on average 261 g (95% CI, 21-502 g) less than those with normal findings.

CONCLUSIONS

In MC twins, abnormal Doppler flow of the umbilical artery identifies a subgroup at risk for preterm delivery, low birth weight and neonatal morbidity, but with a similar mortality risk to those with normal Doppler flow. At term, mortality occurred only in the group with normal Doppler findings, suggesting that fetal surveillance is insufficient in uncomplicated term MC twin pregnancies.

Mise en évidence des anastomoses vasculaires par la vélocimétrie doppler dans les grossesses gémellaires monochoriales. Revue de la littérature à propos de trois cas

Three cases of intermittent absent end-diastolic and reversed end-diastolic flow velocity (A/REDV) are reported in the proximal umbilical artery of the growth-retarded twin in monochorionic twin pregnancies. This typical doppler velocimetric pattern has been related to arterio-arterial anastomoses in two cases of intra-uterine growth retardation and in one case of twin-twin transfusion syndrome. According to the literature, superficial arterio-arterial anastomoses may be detected by doppler colour velocimetry in 75 to 85% of cases, while identification of arteriovenous connections is more difficult to be documented in vivo (50% of cases in experienced hands). The role of superficial vascular anastomoses, either arterio-arterial or venovenous, and that of deep arteriovenous communications is now well documented in the main complications of monochorionic pregnancies, particularly for twin-twin transfusion syndrome, intrauterine growth retardation, intrauterine fetal death and acardiac twins.

Stage I twin-twin transfusion syndrome: rates of progression and regression in relation to outcome

OBJECTIVES

Twin-twin transfusion syndrome (TTTS) results in high rates of perinatal mortality and neurological morbidity. Fetoscopic laser ablation of placental anastomoses is now established as the treatment of choice for advanced disease. However, there remains controversy about its use in early-stage TTTS, in which laser-related fetal losses need to be balanced against relatively favorable outcomes with more conservative approaches. We investigated rates of progression and regression in Stage I TTTS and determined factors influencing the course of the disease.

METHODS

We undertook a retrospective observational study of all TTTS cases referred to our tertiary referral fetal medicine service from 2000 to 2006. In patients presenting with Stage I TTTS, the following variables were evaluated for their ability to predict the course and progression of the disease: gestational age (GA) at presentation, amniotic fluid index, recipient and donor deepest vertical pool, presence of artery-artery anastomoses, small-sized bladder compared to normal donor bladder and fetal size discordance. Study end-points were disease regression or progression, and neonatal survival at 28 days.

RESULTS

Among 132 consecutive cases of TTTS, 46 women presented with Stage I disease. In the majority (69.6%), disease remained stable (28.3%) or regressed (41.3%). Of cases that progressed, 79% did so within 2 weeks and 93% progressed to at least Stage III. No factor was significantly linked with progression or regression, although there was a trend towards the absence of an artery-artery anastomosis (P = 0.10) and the presence of a small rather than normal donor bladder (P = 0.10) influencing progression, and later GA at presentation (P = 0.07) influencing regression. At least one infant survived in 83% of cases and there was double survival in 59%. Perinatal outcome was significantly better in cases that regressed (the rates of at least one survivor and double survival being 89% and 89%, respectively) or remained Stage I (77% and 61%, respectively), compared with those cases that progressed (79% and 14%, respectively). Treatment with amnioreduction at first presentation did not influence progression or regression.

CONCLUSIONS

This study demonstrates that a high percentage of Stage I TTTS cases regress or remain early stage. Identification of factors predicting progression would facilitate the selection of patients for definitive therapy, while avoiding treatment-related morbidities in mild or transient disease.

Percent absent end-diastolic velocity in the umbilical artery waveform as a predictor of intrauterine fetal demise of the donor twin after selective laser photocoagulation of communicating vessels in twin-twin transfusion syndrome

OBJECTIVE

Absent end-diastolic velocity (AEDV) in the umbilical artery of the donor twin is a known risk factor for intrauterine fetal demise (IUFD) of this fetus after selective laser photocoagulation of communicating vessels (SLPCV) for twin-twin transfusion syndrome (TTTS). The aim of this study was to assess the proportion of time, expressed as a percentage, of the cardiac cycle spent in AEDV (%AEDV) as a predictor of IUFD of the donor.

METHODS

All patients referred for possible SLPCV underwent complete preoperative staging evaluation including Doppler assessment of the umbilical artery. %AEDV was calculated retrospectively as 100 x (time of the cycle spent in AEDV divided by duration of total cardiac cycle). Patients without AEDV were considered to have a %AEDV of 0. Follow-up Doppler studies were performed 16-24 h after SLPCV. IUFD of the donor was recorded if the donor twin died any time prior to delivery.

RESULTS

Of 401 patients undergoing SLPCV, 127 had AEDV. Preoperative AEDV of the donor twin was associated with an increased risk of IUFD of the donor (40.9% vs. 14.2%, P < 0.0001). %AEDV was measured in 72/127 (56.7%) donors with AEDV for whom digital images were available. Within these 72 patients, the mean %AEDV was significantly higher in patients with IUFD of the donor (36.5% vs. 29.6%, P = 0.01). IUFD of the donor was similar in patients with AEDV, regardless of whether %AEDV was measured (36% vs. 47%, P = 0.2). A %AEDV > 30 was associated with a 4.3-fold increase in the risk of IUFD of the donor (95% CI, 1.4-12.7), a sensitivity of 77% and a negative predictive value of 81.3%. Logistic regression showed that %AEDV, but not number of anastomoses, placental location, presence of artery-to-artery anastomoses or the presence or absence of EDV was associated significantly with IUFD of the donor.

CONCLUSION

%AEDV is a novel Doppler parameter in the assessment of patients with TTTS. %AEDV, rather than AEDV alone, is a significant risk factor for IUFD of the donor twin and %AEDV > 30 is associated with an increased risk of IUFD of the donor in TTTS patients treated with SLPCV. Assessment of %AEDV should be considered part of the preoperative evaluation of TTTS patients.

The role of laser surgery in dissecting the etiology of absent or reverse end-diastolic velocity in the umbilical artery of the donor twin in twin-twin transfusion syndrome

OBJECTIVE

This study was undertaken to gain insight on the cause of absent or reverse end-diastolic velocity (AREDV) in the umbilical artery (UA) of the donor twin by analysis of individual placental mass and vascular anastomoses in patients with twin-twin transfusion syndrome (TTTS) treated with laser.

STUDY DESIGN

TTTS patients who successfully underwent selective laser photocoagulation of communicating vessels (SLPCV), 16 and 26 weeks' gestation, with both twins born alive and complete Doppler and placental data were considered eligible for the study. Doppler examination of the UA was performed before and 24 hours after SLPCV. Abnormal UA Doppler findings were defined as persistent AREDV. Pre- and post-SLPCV UA Doppler results yielded the following 4 groups: (1) normal-normal; (2) normal-abnormal; (3) abnormal-normal; and (4) abnormal-abnormal. The types of vascular anastomoses were categorized during surgery. Individual placental territory (IPT) was defined as individual placental weight divided by total placental weight x 100.

RESULTS

There were 132 cases in group 1 and no patients in group 2. AREDV resolved in 78% (28/36) of patients (group 3) and remained unchanged in 22% (8/36) (group 4). The mean IPT-donor in group 4 was significantly smaller than in group 1 (P = .015). Patients with preoperative AREDV (groups 3 and 4) were more likely to have artery-to-artery anastomoses (P = .002). However, AREDV resolved in 57% (16/28) patients without artery-to-artery anastomoses.

CONCLUSION

Preoperative AREDV may result from a small IPT, placental vascular anastomoses, or both. AREDV resulting from a small IPT may have a similar cause to that of singletons, and may be inferred by lack of postoperative resolution. Resolution of AREDV after SLPCV implies the presence of an adequate IPT and removal of donor hypotension.

Unequal placental sharing and birth weight discordance in monochorionic diamniotic twins

OBJECTIVE

The purpose of this study was to define the association between unequal placental sharing and birth weight discordance in monochorionic/diamniotic twin pregnancies.

STUDY DESIGN

The study comprised a prospective cohort of monochorionic/diamniotic twin pregnancies who were delivered in Kaiser Permanente-Northern California, 1997-2003. Dye injection studies of fresh postpartum placentas were performed. Placental sharing, cord insertion combinations, vascular anastomoses, gestational age, and birth weights were recorded. Statistical comparisons of birth weight and gestational age were made with the Student t test. Rates of birth weight discordance were compared with the chi-square test. Multivariate logistic regression models analyzed the relationship between variables of interest.

RESULTS

Mean birth weights for larger and smaller twins were 2400 g and 2109 g, respectively. Twenty-two percent of the monochorionic/diamniotic twin pairs had birth weight discordance > or = 20%, and 8% of these pairs had twin-twin transfusion syndrome. Monochorionic/diamniotic twin pairs with unequal placental sharing had a 9.8 times greater likelihood of birth weight discordance (95% CI, 5.4-17.9) as compared with those pairs with equal placental sharing.

CONCLUSION

Unequal placental sharing is a significant risk factor for birth weight discordance in monochorionic/diamniotic twins. Antenatal diagnosis of unequal placental sharing would enable improved counseling in the setting of monochorionic/diamniotic twins.

The management of multiple pregnancy

The epidemic of multiple pregnancy continues albeit in a different form with twin pregnancies predominating. Determination of chorionicity is the key to management and regular monitoring by ultrasound is a hallmark of quality care. All multiple pregnancies should be offered first trimester screening by nuchal translucency for aneuploidy. MC twins should be scanned at fortnightly intervals to allow complications such as twin-twin transfusion or IUGR to be detected and referral made to a fetal medicine centre. Maternal complications are common and vigilance is required for their detection. Although planned vaginal delivery can often be achieved, mothers must be prepared for the substantial risk of requiring a caesarean section as this currently occurs in the majority.

Recent findings on laser treatment of twin-to-twin transfusion syndrome

PURPOSE OF REVIEW

Despite the recent demonstration of the benefit of the primary laser over amnioreduction, overall survival is far from optimal (70-80%), and therefore diagnosis and management of early and late complications following placental surgery became of great importance.

RECENT FINDINGS

Laser therapy has proven to be better than amnioreduction in treating twin-to-twin transfusion syndrome. Miscarriage, preterm premature rupture of the membranes and preterm delivery account for more than 20% of perinatal mortality after treatment. In those who die despite treatment, recurrence of twin-to-twin transfusion syndrome, placental insufficiency or feto-fetal hemorrhage with anemia/polycythemia are complications that have to be managed with different secondary therapeutic options, such as amnioreduction, cord coagulation, intrauterine transfusion or repeat fetoscopy-guided laser. Ex-vivo placental angiography has confirmed that these complications occur when anastomoses are missed. Early predictors of laser efficacy in twin-to-twin transfusion syndrome treatment, such as improvement in the umbilical vein flow imbalance and urine production, are being evaluated, because they are earlier predictors of outcome than amniotic fluid discordance.

SUMMARY

Optimization of laser treatment of twin-to-twin transfusion syndrome and new insight into the follow-up are likely to become the key to a better prognosis, and they are therefore important issues that have to be addressed in forthcoming studies.

Determinants of flow along arterio-arterial anastomoses in monochorionic placentae by dynamic computer modelling of chorionic plate vasculature

OBJECTIVES

To investigate anatomical and physiological determinants of inter-fetal transfusion along arterio-arterial (AA) anastomoses in monochorionic placentae.

METHODS

A computer model of chorionic arterial vasculature was constructed in QuickBASIC using data collected from experimentation and the published literature. After validating the model, the influence of various physiological and anatomical variables on anastomotic flow rates was examined.

RESULTS

AA anastomotic flow rates were significantly related to changes in fetal mean arterial pressure (p < 0.0001) and heart rate (p < 0.0005). AA flow rates were also related to the imbalance in number of arterio-venous (AV) anastomoses, to placental territory share, and to the branch number of the AA anastomosis (AAAs) from the chorionic arterial tree.

CONCLUSIONS

Net blood flow and direction along AA anastomoses are influenced by fetal cardiac output, by the presence of compensatory AV anastomoses, and by the branch number of the chorionic arteries connected by the anastomosis. This study provides insight into the determinants of chronic transfusional imbalance as well as acute inter-fetal transfusion.

[Twin-twin transfusion syndrome and cardiovascular complications]

INTRODUCTION

Twin-twin transfusion syndrome carries high morbidity and mortality, related in part to the cardiovascular alterations that it produces.

CASE REPORT

Patient 1 underwent a cesarian section at week 28 due to myocardial dysfunction and severe tricuspid regurgitation in the recipient twin. Twelve hours after birth the recipient twin developed refractory shock. Severe biventricular hypertrophy was observed and the twin died 60 hours after birth from multisystemic failure. Patient 2 underwent a cesarian section at week 29 due to cardiomegaly and cardiac insufficiency in the recipient twin. At birth, he showed hypertension and poor peripheral perfusion. Biventricular hypertrophy was observed, which increased until it produced a mild right midventricular stenosis at 72 hours, decreasing after the 8th day. Mild hypertrophy persisted at 6 months of life.

DISCUSSION

Cardiovascular alterations appear only in recipient fetuses affected by twin-twin transfusion syndrome. The most frequent findings are cardiac dilation, hypertrophy, myocardial dysfunction, tricuspid regurgitation and pulmonary stenosis. These alterations usually disappear during the first few months of life, but may also worsen.

What--and why--the pediatric surgeon should know about twin-to-twin transfusion syndrome

Abstract Endoscopic laser ablation of placental vessels is the most commonly performed fetal operation today. Herein, we review the pathophysiology of twin-to-twin transfusion syndrome and the challenges of its treatment. Pediatric surgeons, with their knowledge of fetal and congenital pathology, and their technical expertise with minimally invasive surgery, can be of great benefit to the patient and the medical team.

Increased latency of absent end-diastolic flow in the umbilical artery of monochorionic twin fetuses

OBJECTIVE

To determine if absent end-diastolic flow (AEDF) in the umbilical artery (UA) has a longer latency in monochorionic (MC) twin fetuses compared to singleton or dichorionic twin (DC) fetuses.

METHODS

One hundred and eight pregnancies with a fetus with AEDF were reviewed: 47 MC and 17 DC twin pregnancies and 44 singletons. Because twin-twin transfusion syndrome (TTTS) is a potential confounder when determining latency, subgroup analysis was also performed on the 21 MC affected pregnancies without TTTS. Latency of AEDF (in days) was defined as the difference between the gestational age at diagnosis of AEDF and gestational age at delivery or intrauterine death.

RESULTS

Latency was similar in MC twins (median, 39 days) and DC twins (30 days) but longer compared to singletons (11 days; P = 0.0001). After excluding pregnancies with TTTS, latency in non-TTTS MC twins (54 days) was longer than in both singletons and DC twins. This was due to an earlier gestational age at AEDF in non-TTTS MC twins of 20 weeks compared to 27 weeks in both singleton and DC twins because median gestational age at delivery was similar in MC twins, DC twins and singletons.

CONCLUSIONS

The latency period of UA AEDF is longer in MC twins than in singletons. Our data suggest that in MC twin fetuses without TTTS, AEDF begins earlier and lasts about twice as long as in DC twin fetuses, which is consistent with placental insufficiency not being the sole factor mediating abnormal UA waveforms in MC placentation. This observation is important in counseling and managing twin pregnancies discordant for AEDF.

Antepartum management of multifetal pregnancies

Correct antepartum management of multifetal gestations is a critical skill for practitioners of obstetrics. This article reviews important issues surrounding these complicated pregnancies while discussing current management options and recommendations. Topics include antepartum surveillance, preterm labor prediction, diagnosis, and management, and special situations unique to multiple gestations, such as twin-twin transfusion syndrome and death of one twin in utero. It is the authors' hope that this article is comprehensive in enhancing the reader's knowledge of these complex pregnancies.

Characterisation of deep arterio-venous anastomoses within monochorionic placentae by vascular casting

OBJECTIVE

To characterise arterio-venous anastomoses (AVA) in monochorionic (MC) placentae and determine (i) whether shared cotyledons lie beneath the co-termination of an artery from one twin and a vein to the contralateral twin and (ii) whether all AVA can be detected by visual inspection of the chorionic plate.

METHODS

Vascular casts were made of 15 MC placentae. The number of typical AVAs suspected visually before digestion was compared with the number of AVAs identified after acid digestion.

RESULTS

Thirty-three of 67 (49%) suspected typical AVAs were confirmed as typical after casting. There were five false positives and no false negatives. The remainder were classified as atypical AVAs, found in > or =90% of MC placentae. Type I (small vascular connections between two apparently normal cotyledons not seen before casting) and Type II (shared cotyledons arising within larger apparently normal cotyledons) atypical AVAs were found in 53% and 73% of placentae, respectively.

CONCLUSIONS

Only half the shared cotyledons in MC placentae are characterised by co-termination of an artery and vein on the chorionic plate. We report the existence of deep anastomoses beneath the chorionic plate that cannot be visualised by chorionic plate inspection. These findings have implications for laser treatment of twin-twin transfusion syndrome.

Insights into the pathophysiology of twin–twin transfusion syndrome

Twin-twin transfusion syndrome (TTTS) is attributed to trans-anastomotic transfusion between twins. Anastomoses are ubiquitous in monochorionic (MC) placentae, yet TTTS develops in only 15%. Although ex vivo and in vivo studies fail to identify a unique anastomotic signature, TTTS placentae are typically associated with an imbalance in unidirectional arteriovenous anastomoses with absent bidirectional anastomoses. Doppler detection of an artery-artery anastomosis reduces the chance of TTTS, whereas, in those that develop the disease, it improves stage-independent survival. Selective laser is often curative, but an increasingly recognized risk of persistent or reverse TTTS may be attributable to atypical arteriovenous anastomoses not identifiable from the chorionic plate. Simple dysvolaemia fails to explain several phenotypic features, including haematological concordancy, recipient hypertension, and reversibly absent end diastolic flow in the donor. The renin-angiotensin system is upregulated in the donor and downregulated in the recipient's kidneys, while paradoxically raised renin levels in the recipient may contribute to raised afterload along with endothelin. Although research is limited in humans by therapy and the lack of a suitable experimental model, further studies of placental and vascular pathophysiology may not only refine current treatment modalities but may also, in addition, suggest further avenues for downstream management such as genetic predisposition testing or pharmacological intervention.

Twin–Twin Transfusion Syndrome: A Population-Based Study

OBJECTIVE

To study the incidence and mortality and morbidity rates of twin-twin transfusion syndrome in a complete population-based cohort in Nova Scotia.

METHODS

A population-based cohort study of all monochorionic diamniotic twin pregnancies of 20 weeks of gestation or longer born to Nova Scotia (Canada) residents between 1988 and 2000 was examined. The effect of gestational age adjustment and birth weight discordancy of more than 20% on mortality and 1-year survival was studied. Other outcomes studied included birth depression, respiratory distress syndrome, chronic lung disease, interventricular hemorrhage, periventricular leukomalacia, acute renal failure, and congestive heart failure.

RESULTS

Of 404 monochorionic-diamniotic twin pregnancies examined, 48 were identified with twin-twin transfusion syndrome. Total mortality rates per pregnancy were significantly greater in the twin-twin transfusion syndrome group than in the remainder of our monochorionic diamniotic population (P < .01). However, when adjusted for gestational age, mortality failed to achieve statistical significance. Similarly, no differences were noted for 1-year survival and other outcomes of liveborn infants after gestational age adjustment. Discordance in birth weight predicted a higher incidence of morbid outcomes per pregnancy, but this effect was lost after gestational age adjustment.

CONCLUSION

Increased morbidity and mortality of twins with twin-twin transfusion syndrome is likely to be due to a higher incidence of preterm birth. Birth weight discordancy was not found to be an independent predictor of mortality after controlling for gestational age and twin-twin transfusion syndrome.

Clinical evaluation of the risk of twin-to-twin transfusion syndrome using the relative power contribution of fetal heart rate fluctuations

OBJECTIVES

In twin pregnancies, it has been suggested that fluctuations of the two fetal heart rates should be considered as two variates that affect each other. We therefore investigated whether the relative power contribution (RPC) of heart rate fluctuation between twins reflects the clinical severity of twin-to-twin transfusion syndrome.

STUDY DESIGN

Sixty-three cases of twin pregnancy including 43 monochorionic twins and 20 dichorionic twins were studied. Thirteen monochorionic twins with polyhydramnios in one twin were regarded as twin-to-twin transfusion syndrome (TTTS). Of the 13 TTTS cases, 8 cases with polyhydramnios in one twin and oligohydramnios in the other were deemed to be a 'stuck' twin. The RPC of the very low frequency domain (VL; 0.0125-0.0625 Hz) of fetal heart rate fluctuation in the twin fetuses of monochorionic and dichorionic pregnancies was obtained within a week of delivery. The relationship between the value of the RPC and the outcome of these twins was examined.

RESULTS

For both monochorionic and dichorionic twins the RPC of twin fetuses was significantly higher in TTTS twins than in twins without TTTS. In particular, in pregnancies that resulted in fetal death, early neonatal death, or hydrops of one of the twins, this twin had a higher RPC than the other twin. No significant difference was observed in the RPC value between twins of either monochorionic or dichorionic pregnancies that did not develop TTTS. Serial changes in RPC values were followed in 7 cases of TTTS. The RPC value rose rapidly just before delivery in three cases with resultant poor outcome.

CONCLUSION

A rapid change in the RPC of twin fetuses measured using the VL frequency domain of fetal heart rate fluctuations may predict poor outcome in twin pregnancies.

Pseudo-arterio-arterial anastomoses in twin–twin transfusion syndrome

OBJECTIVE

It has recently been claimed that fetoscopic recognition of a haemodynamic equator within an arterio-arterial anastomosis (AAA) suggests minimal net intertwin flow. This was based on blood from one fetus being dark and from the other bright red, the boundary between them reciprocating with the fetal heart beats. However, bright red indicates that the blood had passed through a cotyledon and been freshly oxygenated, which should be impossible in an AAA. We applied a computer model of chorionic vessels to determine a configuration that reproduced this phenomenon.

METHODS

A previously published TTTS model was extended to provide placental detail in a segment containing four cotyledons of each placenta supplied by three generations of placental arteries and veins.

RESULTS

Reciprocating flow is not unique to AAAs. It also occurs in the chorionic arteries of any cotyledon deprived of its venous outflow, in a similar manner to that in which reverse end-diastolic flow occurs in umbilical arteries when whole placental resistance is high. If venous return from the common chorionic vein in the recipient (draining the venous end of an AVA) is blocked as might happen after laser, there can be bidirectional flow from one umbilical artery insertion, through two cotyledons to the other insertion. We define this phenomenon as a pseudo-AAA (PAAA). The inclusion of two cotyledons in this path means that its resistance cannot match the low flow resistance of a true AAA, and transmission of the contralateral pulsatile pattern is absorbed in the cotyledons. Thus, PAAA Doppler patterns differ from true AAA patterns in that two sets of systolic peaks, one forward and one reverse, can be discerned in true AAAs but only one in PAAAs.

CONCLUSIONS

We demonstrate how venous occlusion of an arterio-venous anastomosis may produce a pseudo-AAA colour equator at endoscopy. However, visual observation of reciprocating flow is not sufficient to define a vessel as a true AAA which instead requires ultrasonical identification of two systolic patterns.

Doppler for Artery–Artery Anastomosis and Stage-Independent Survival in Twin–Twin Transfusion

OBJECTIVE

Treatment selection in twin-twin transfusion syndrome is increasingly determined by disease severity. We investigated whether detection of arterio-arterial anastomoses predicts perinatal survival.

METHODS

An artery-artery anastomosis was sought by Doppler and disease stage was determined in 105 cases of twin-twin transfusion syndrome at presentation, first treatment, and worst stage. Outcome measures were perinatal, double, and any (1 or more babies) survival rates.

RESULTS

After exclusion of 10 noninformative pregnancies, perinatal, double, and any survival rates were 61%, 44%, and 77%, respectively. When an anastomosis was detected at each of the 3 time points, perinatal and double survival rates were higher than when one was not (at first treatment, perinatal survival 83% versus 53%, respectively, P =.003; double survival 78% versus 33%, P <.001). Perinatal and double survival (P < or =.01) were poorer with more advanced stage, but any survival rates were not influenced by stage or anastomosis detection. Multiple logistic regression demonstrated that anastomosis detection at treatment increased the chance of perinatal (odds ratio [OR] 5.1, 95% confidence interval [CI] 1.6, 15.9) and double survival (OR 19.3, 95% CI 2.7, 138), independently of stage. For stages I-III at treatment, anastomosis detection predicted better perinatal (100% versus 63%, 100% versus 59%, and 83% versus 44%, respectively) and double survival rates (100% versus 52%, 100% versus 46%, and 78% versus 26%). Stage III, with anastomoses detected, had better perinatal (83% versus 63%) and double survival (78% versus 52%) than did stage I without detection.

CONCLUSION

Antenatal detection of artery-to-artery anastomosis predicts higher perinatal and double survival in twin-twin transfusion syndrome, independently of disease stage.

LEVEL OF EVIDENCE

II-3

Limited Prognostic Value of a Staging System for Twin-to-Twin Transfusion Syndrome

OBJECTIVE

Severe twin-to-twin transfusion syndrome (TTTS) is usually classified according to a staging system (I-V) based on ultrasonographic findings of polyhydramnios in the recipient, oligohydramnios in the donor, the presence or absence of the donor's bladder, Doppler waveform changes and (impending) hydrops. Stage correlates with the severity of disease, and it is assumed that, without intervention, severe TTTS will evolve in succession from stage I to stage V (fetal demise). However, this progression has not been validated in longitudinal studies. Herein, we report on the natural progression of severe TTTS in a cohort of patients from a regional Fetal Treatment Program.

METHODS

Eighteen patients with severe TTTS, diagnosed between 15 and 25 weeks of gestation, were managed over a 28-month period. Data were collected until delivery, endoscopic surgical intervention or dual fetal demise. Patients were evaluated at least once a week. Stage, estimated fetal weight, percent recipient/donor body weight discordance and survival were recorded.

RESULTS

The present study represents a total follow-up of 108 patient-weeks. Of 90 week-to-week evaluations, 65 showed no change in stage; 11 showed downstaging (by more than 1 stage in 3, or 27%), and 13 showed upstaging (by more than 1 stage in 8, or 62%). Nine patients (all stage II or above) underwent endoscopic laser ablation. Overall survival was 67%, and survival of at least 1 twin occurred in 78% of pregnancies. Weight discordance between the donor and recipient did not predict outcome.

CONCLUSION

The current staging system for severe TTTS may not be helpful in predicting the direction, degree or speed of progression of the condition. Indications for intervention should remain stage-related, and not based on projected progression.

Occlusion of Arterio-Arterial Anastomosis Manifesting as Acute Twin–Twin Transfusion Syndrome

In vivo, ex vivo and modelling studies suggest that arterio-arterial anastomoses (AAAs) protect against haemodynamic imbalance in monochorionic twins and thus the development of TTTS. We report the acute onset of severe TTTS at 34 weeks' gestation in a patient with an antenatally visualized AAA which was shown at injection studies to have been obliterated, presumably by thrombosis. Computer modelling with the relevant clinical data confirmed that occlusion of the AAA alone was sufficient to reproduce the clinical manifestations. A study of the vascular configuration of AAA in the fixed placenta suggested that its small diameter and turbulent flow may have contributed to its occlusion. This case report shows that the unmasking of unbalanced AVA configurations by occlusion of a protective AAA can manifest as TTTS.

Stratégies de diagnostic prénatal et prise en charge des pathologies liées aux grossesses multiples

In the first trimester, ultrasound is crucial to screen for aneuploidies based on nuchal translucency, to diagnose major birth defects, and to establish chorionicity. Indeed prenatal diagnosis strategies as well as obstetrical management options are largely based on placental type. In the second trimester, maternal serum screening is not as effective, and ultrasound screening is more difficult in twins than in singletons. When a severe abnormality in found in one twin, selective termination of pregnancy may be considered. This technique is safe in dichorionic twins, but hazardous in monochorionic pregnancies. Selective termination in dichorionic twins is safer in the first trimester, underscoring the need for early prenatal diagnosis in twins. Monochorionic twin pregnancies carry specific risks, such as the twin-to-twin transfusion syndrome, which can be treated by endoscopic photo-coagulation of intertwin anastomoses in the severe early onset cases, or by amnioreduction in milder cases.

Hemodynamic changes with phenotype reversal during pregnancy in twin-twin transfusion syndrome

OBJECTIVES

We report an atypical case of twin-twin transfusion syndrome (TTTS) in monochorionic-diamniotic twins with arterio-arterial anastomoses in which the former donor became the recipient during pregnancy.

METHODS

Serial sonographic monitoring was performed.

RESULTS

There was a phenotype reversal in TTTS concerning growth and amniotic fluid ending at 27 weeks, with the dominance of the former smaller donor. Doppler sonography changed from absent enddiastolic flow of the donor to normal values in both twins. The new recipient showed transient ascites, the now smaller actual donor (former recipient) developed progressive cardiomegaly, hypertrophy of the myocardium and mitral and tricuspid insufficiency at 29 weeks. Doppler sonography in the new donor deteriorated to highly pathologic flow in the venous system, leading to cesarean section. The donor fetus died 12 h after delivery because of myocardial decompensation. The recipient did very well and was discharged 8 weeks later from the neonatology unit.

CONCLUSION

This atypical course shows the importance of serial sonographic monitoring in pregnancies with TTTS.

The role of Doppler studies in predicting individual intrauterine fetal demise after laser therapy for twin-twin transfusion syndrome

OBJECTIVE

To investigate the role of Doppler studies in predicting individual fetal demise in patients scheduled for selective laser photocoagulation of communicating vessels (SLPCV) for twin-twin transfusion syndrome (TTTS).

METHODS

Doppler studies of the umbilical artery, umbilical vein, ductus venosus, tricuspid valve regurgitation and middle cerebral artery were performed in the donor and recipient twins before and 24 hours after SLPCV. Results were analyzed cross-sectionally and longitudinally. As multiple comparisons were made, an a priori alpha rejection was set at P < 0.001.

RESULTS

One hundred and ten consecutive patients were available for analysis. Overall fetal survival was 68.6% (151/220) with at least one survivor in 88.2% (97/110) of cases. Absent or reversed end-diastolic velocity in the umbilical artery of the donor twin was the only preoperative Doppler result predictive of intrauterine fetal demise (IUFD) (10/15, 66.7%, P < 0.001). Postoperatively, reversed flow during atrial contraction in the ductus venosus of the donor twin showed a trend towards prediction of IUFD of this fetus (4/5, 80%, P = 0.007). No other Doppler studies, including the longitudinal analyses, were predictive of IUFD.

CONCLUSIONS

Our data suggest that preoperative absent or reversed end-diastolic velocity in the umbilical artery may be useful in predicting individual fetal demise of the donor twin in TTTS patients scheduled for SLPCV. This may reflect the role of decreased individual placental mass that may be associated with some donor twins. The inability of other Doppler studies to predict individual IUFD may be explained preoperatively by the effect of the interfetal vascular connections on the individual Doppler signals and postoperatively by the effect of surgery or the timing of the assessment. Our findings may be important in patient counseling, in furthering understanding of the disease, and perhaps in improving surgical technique.

Fetal hypertension: an insight into the pathogenesis of the twin-twin transfusion syndrome

OBJECTIVES

To investigate if systemic hypertension occurs in fetuses with twin-to-twin transfusion syndrome (TTTS).

METHODS

We conducted an observational cohort study in a tertiary care centre in 23 pregnant women with TTTS. Polyhydramnios stuck twin sequence occurred at a median gestational age of 22 weeks (range 15-27). Biventricular myocardial hypertrophy was diagnosed in 22/23 recipient fetuses. In cases with atrioventricular valve regurgitation (AVR), it was possible to estimate the fetal systolic systemic blood pressure by ultrasound, on the basis of the simplified Bernouilli equation. The diagnosis of fetal hypertension (FHT) was made when the estimated systolic arterial pressure was equal to or above 1.6-fold the expected value.

RESULTS

In 10 pregnancies (group A), fetal blood pressure could be assessed in recipients with AVR. The maximum velocities ranged from 2.9 to 5 m/s, leading to estimates of systemic fetal arterial pressure from 37 to 104 mmHg, that is, 1.6- to 2.8-fold the expected values. In 13 pregnancies (group B), fetal blood pressure could not be assessed in the absence of AVR. In group A, perinatal death (16/20) and hydrops (7/20) were significantly more frequent than in group B (8/26 and 1/26 respectively).

CONCLUSION

Fetal systemic hypertension may occur in recipient twins and could play a role in the pathophysiology of TTTS.