Placental Characteristics in Monochorionic Twins With and Without Twin Anemia–Polycythemia Sequence

Artery-to-vein anastomoses in unequally divided placentas and their association with birthweight discordance

INTRODUCTION

This study investigated the impact of the shared intertwin circulation in unequally divided monochorionic (MC) placentas on fetal growth.

METHODS

This retrospective analysis included color-dyed, unequally shared placentas from two tertiary centers. Exclusions included twin-twin transfusion syndrome, twin anemia polycythemia sequence, and lethal anomalies. Measurement of the external diameters and areas of the artery-to-artery (AA), artery-to-vein (AV), and vein-to-vein (VV) anastomoses was performed. The ratio of the shared circulation (AV ratio) was determined by comparing the areas of the summed venous components of shared AV anastomoses to those in the individual AV anastomoses of the smaller placental part. The birth weight ratio/placental ratio (BWR/PR), total AV size areas and net AV transfusion were calculated. Univariable and multivariable linear regressions were performed to assess the relationship between BWR/PR, the AV ratio, the areas of the different anastomoses and cord insertion discordance.

RESULTS

Among 352 placentas, 97 % (340) had intertwin AV anastomoses, and 50 % (176) were from pregnancies with selective growth restriction. The AV ratio, AA, VV, total AV areas, and cord insertion discordance negatively correlated with BWR/PR. Multivariable linear regression confirmed the independent negative association between BWR/PR and the AV ratio, suggesting that a larger shared circulation benefits the twin with the smaller placental part. Type III sFGR placentas exhibited the highest AV ratio, resulting in the lowest BWR/PR.

DISCUSSION

A larger shared circulation mitigates the impact of an unequally divided placenta on fetal growth. This effect surpasses the influence of AA and VV diameters and is most prominent in Type III sFGR placentas.

The High-Risk Profile of Selective Growth Restriction in Monochorionic Twin Pregnancies

The present review aims to provide a critical appraisal of the sonographic diagnosis and follow-up and to evaluate the optimal clinical management of monochorionic twin pregnancies where one of the twins is complicated by selective fetal growth restriction (sFGR). The classification is based on the umbilical artery (UA) diastolic flow reflecting the outcome. If the sFGR twin has positive diastolic flow (Type I) then the prognosis is good, and it does not require close surveillance. Biweekly or weekly sonographic and Doppler surveillance and fetal monitoring are recommended strategies to detect unpredictable complications in type II and type III forms, which are defined by persistently absent/reverse end-diastolic flow (AREDF) or cyclically intermittent absent/reverse end-diastolic flow (iAREDF) in the umbilical waveforms, respectively. The latest forms are associated with an increased risk of unexpected fetal demise of the smaller twin and 10-20% risk of neurological injury in the larger twin in addition to the overall risk of prematurity. The clinical course can be affected by elective fetal therapy ('dichorinization' of the placenta with laser or selective fetal reduction) or elective delivery in the presence of severe fetal deterioration. The prediction of the clinical outcome in complicated cases of type II and III sFGR cases remains elusive. Novel routines in fetal and placental scans in order to predict neurological impairments and unexpected fetal death to optimize the delivery time-point are needed.

Twin Anemia-Polycythemia Sequence (TAPS): From Basic Research to Clinical Practice

Twin pregnancy is associated with an increased risk of perinatal and maternal complications, and early establishment of the chorionicity type defines this risk. In monochorionic (MC) pregnancies, the fetuses share the same placental mass and exhibit vascular anastomoses crossing the intertwin membrane, and the combination and pattern of anastomoses determine the primary clinical picture and occurrence of future complications. Twin Anemia-Polycythemia Sequence (TAPS) was first described in 2006 after fetoscopic laser surgery in twin-to-twin transfusion syndrome (TTTS) twins, and in 2007, the first spontaneous cases were reported, recognizing TAPS as an individualized vascular identity in fetofetal transfusion syndromes. There are two types of TAPS: spontaneous (3-5%) and iatrogenic or postlaser (2-16%). TAPS consists of small diameter arteriovenous anastomoses (<1 mm) and low-rate, small-caliber AA anastomoses in the absence of amniotic fluid discordances. There are certain antenatal and postnatal diagnostic criteria, which have progressively evolved over time. New, additional secondary markers have been proposed, and their reliability is being studied. The best screening protocol for TAPS in MC twins is still a matter of debate. This review provides a survey of the relevant literature on the epidemiology, vascular pathophysiology, underlying hemodynamic factors that regulate mismatched vascular connections, and diagnostic criteria of this condition. The aim is to increase awareness and knowledge about this recently identified and frequently unrecognized and misdiagnosed pathology.

Umbilical venous diameter and flow in monochorionic diamniotic twin pregnancy: association with placental sharing and fetal demise

OBJECTIVE

To examine the association of umbilical venous diameter and flow in monochorionic diamniotic twin pregnancy with placental sharing and fetal demise.

METHODS

This was a prospective longitudinal cohort study of a consecutive series of monochorionic diamniotic twin pregnancies that underwent ultrasound assessments at 12, 16, 20 and 28 weeks' gestation. Fetal biometry (crown-rump length at 12 weeks or estimated fetal weight (EFW) thereafter) and cord insertion sites were recorded at each visit, as well as the diameter of the umbilical vein (UV) in both the intra-abdominal part and a free loop of the umbilical cord. Time-averaged maximum velocity in the intra-abdominal part of the UV was measured to calculate UV-flow. Univariate and multivariate linear regression analyses were performed to assess the relationship between intertwin ratios of these variables and placental sharing at 12, 16, 20 and 28 weeks' gestation. Placental sharing was calculated by dividing the larger by the smaller placental share, as measured on placental injection studies after birth. Additionally, the Mann-Whitney U-test and receiver-operating-characteristics-curve analysis were used to explore the relationship between the occurrence of fetal demise and intertwin differences in fetal biometry, cord insertion sites, UV diameters and flow at 12, 16, 20 and 28 weeks.

RESULTS

Of 200 consecutive monochorionic twin pregnancies enrolled, injection studies were performed in 165 (82.5%) placentas. On univariate analysis, intertwin differences in fetal biometry, cord insertions and UV variables were associated significantly with placental sharing at 12, 16, 20 and 28 weeks' gestation. On multivariate analysis, intertwin differences in fetal biometry, cord insertions and all three UV variables remained associated significantly with placental sharing at 12 and 16 weeks. However, at 20 and 28 weeks, only the intertwin EFW ratio was associated consistently with placental sharing. Fetal demise of one or both twins complicated 26 (13.0%) pregnancies. Differences in EFW and cord insertion sites were not associated significantly with fetal demise, while at 16 weeks, differences in intra-abdominal UV diameter and flow were associated with an increased risk of subsequent fetal demise.

CONCLUSIONS

At 12 and 16 weeks' gestation, intertwin differences in UV diameter and flow reflect placental sharing more accurately than do differences in fetal growth and cord insertion sites. At 16 weeks, discordance in intra-abdominal UV diameter and flow is also associated with an increased risk of fetal demise. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Clinician-reported Chorionicity and Zygosity Assignment using single-nucleotide polymorphism-based cell-free DNA Lessons learned from 55,344 Twin Pregnancies

Objective

Prenatal chorionicity assessment relies on ultrasound, which can be confounded by many factors. Noninvasive assessment of zygosity is possible using single nucleotide polymorphism (SNP)‐based cell‐free DNA testing. Our objective was to determine the relationship between provider‐reported chorionicity and SNP‐cfDNA assignment of twin zygosity.

Methods

All twin pregnancy blood samples received by a reference laboratory between September 27, 2017 and September 8, 2021 were included. Chorionicity assignment was requested on the requisition, recorded as; monochorionic (MC), dichorionic, or “don't know”. SNP‐cfDNA zygosity results, monozygotic (MZ) or dizygotic (DZ), were correlated with chorionicity assignment.

Results

59,471 twin samples (median gestational age = 12.0 weeks at draw) were received and analyzed; 55,344 (93.1%) received zygosity assignment. SNP‐cfDNA reported 16,673 (30.1%) MZ and 38,671 (69.9%) as DZ. Provider‐reported chorionicity was compared to the zygosity assignment for each case. Of 6283 provider‐reported MC twins, 318 (5.1%) were reported as DZ using SNP‐cfDNA.

Conclusion(s)

One in 20 suspected MC twin pregnancies were reported as DZ using SNP‐cfDNA. Approximately 30% of 55,344 twin pregnancies were found to be MZ, including cases where chorionicity was unknown. SNP‐cfDNA zygosity assessment is a useful adjunct assessment for twin pregnancies, particularly those reported as MC or without determined chorionicity.

What's already known about the topic?

The assignment of chorionicity early in pregnancy can improve perinatal outcomes of twin pregnancies. Prenatal assessment of chorionicity relies on ultrasound (US), and the accuracy of US can be confounded by many factors, including gestational age (GA) and operator experience. Noninvasive assessment of zygosity is now possible using single nucleotide polymorphism (SNP)‐based cell‐free DNA (cfDNA).

What does this study add?

This is the first population‐based study describing the correlation between cfDNA assessment of zygosity and chorionicity. In 55,344 twin pregnancies, approximately 30% were found to be monozygotic (MZ), including cases where chorionicity was unknown. We found that one in 20 suspected monochorionic (MC) twin pregnancies were reported as dizygotic (DZ) twins (DZ) by SNP‐cfDNA testing. SNP‐cfDNA zygosity assessment is a useful adjunct assessment for twin pregnancies, particularly those reported as MC or without determined chorionicity.

Are there differences between monochorionic twin placentas after spontaneous and assisted conception?

INTRODUCTION

No data are available on the placental characteristics of monochorionic twin pregnancies conceived by in vitro fertilization (IVF). This study investigates the differences between placentas from monochorionic diamniotic (MCDA) twin pregnancies conceived spontaneously and those conceived after IVF.

METHODS

This is a retrospective analysis of placental data from a consecutive series of MCDA twin pregnancies followed from the first trimester. The following placental characteristics were compared between IVF versus spontaneous MCDA pregnancies: placental sharing and birth weight discordance relative to placental sharing, the placental angioarchitecture (number, type, and size of anastomoses), and the umbilical cord insertion types.

RESULTS

Of the 256 MCDA placentas included in this analysis, 32 (12%) were conceived through IVF and 224 (88%) spontaneously. MCDA twin placentas after IVF did not differ significantly from MCDA twin placentas after spontaneous conception regarding placental sharing, birthweight discordance relative to sharing discordance, and angioarchitecture. There was a trend toward more discordant cord insertions (combination eccentric and velamentous) in IVF (25%) than in spontaneously conceived placentas (12%) (P = 0.05).

DISCUSSION

No differences could be demonstrated between MCDA placentation after spontaneous conception and IVF. Any differences in pregnancy outcome between spontaneous and IVF conceived MCDA twins may not be related to differences in placental sharing, angioarchitecture and cord insertion type.

Pathophysiology, diagnosis, and management of twin anemia polycythemia sequence in monochorionic multiple gestations

Twin anemia polycythemia sequence (TAPS) is a consequence of unequal sharing of red blood cells between monochorionic twins resulting in anemia in the donor and polycythemia in the recipient twin. Prenatally TAPS can occur spontaneously or complicate incomplete laser surgery for twin transfusion syndrome. While there may be clinical overlap with twin transfusion syndrome or selective fetal growth restriction, diagnosis relies on Doppler measurement of middle cerebral artery peak systolic velocities. Significantly discordant velocities are diagnostic, while severity staging is based on signs of cardiovascular compromise. Conservative management, fetoscopic laser coagulation, selective twin reduction, fetal blood and exchange transfusion, and delivery may be selected guided by the gestational age of diagnosis, the severity of the condition, the likelihood of success, and the patients' priorities. Prenatal curative treatment that minimizes the risk for prematurity and residual morbidity at birth is most likely to offer the greatest short-term and long-term benefits.

What fetal medicine specialists should know about the monochorionic placenta

Monochorionic twins are at risk of transfusion imbalances as long as they are connected to the shared placenta during their intrauterine journey. This review article addresses the macroscopic examination of the monochorionic placenta at the time of birth and explains placental dye injection studies to document the vascular anastomoses and placental sharing. We elaborate on the different types of anastomoses, the importance of how the placenta is divided between the twins, and the angioarchitecture in twin-twin transfusion syndrome, twin anemia polycythemia sequence and selective fetal growth restriction.

The association between vein-to-vein anastomoses and birth weight discordance in relation to placental sharing in monochorionic twin placentas

INTRODUCTION

This study aims to examine the association between the presence and size of a vein-to-vein (VV) anastomosis and birth weight discordance relative to placental discordance in monochorionic diamniotic twin pregnancies.

METHODS

Placentas of two previous prospective studies were included in this retrospective analysis. After injection with color dye, we measured the placental surface of each twin and VV, artery-to-artery (AA), and artery-to-vein (AV) anastomoses on a digital photograph. We calculated the birth weight ratio (BWR), placental ratio (PR), and birth weight ratio/placenta ratio (BWR/PR), as well as total AV size and net AV transfusion. Placental characteristics were compared between placentas with and without VV anastomoses. We performed univariate analyses to assess the following predictors for BWR/PR: VV size, AA size, total AV size, and net AV transfusion. Multivariate analysis was then performed, including the variables significant in univariate analysis.

RESULTS

We analyzed 247 placentas: 58 (23%) with VV anastomoses and 189 without (77%). The BWR and PR were higher in the group with VV. In contrast, BWR/PR was lower in the group with VV anastomoses than in those without. The size of AA anastomoses was larger in placentas with VV anastomoses than in those without. In univariate analysis, VV size and AA size were significantly associated with BWR/PR. However, in multivariate regression, only VV size remained significantly associated with the BWR/PR.

DISCUSSION

VV anastomoses are associated with a decreased birth weight discordance relative to the placental sharing discordance, independent of the AA anastomoses.

Monochorionic diamniotic twin pregnancies

About one in five twin pregnancies are monochorionic diamniotic. In these twins, transfusion imbalances may develop due to the invariably present vascular anastomoses. The most severe imbalance is twin-twin transfusion syndrome, which presents as a significant amniotic fluid difference diagnosed on ultrasound scan, usually before 26 weeks. Another transfusion imbalance is twin anemia polycythemia sequence, a severe hemoglobin difference occurring mainly after 26 weeks in previously uncomplicated pregnancies. Fetoscopic laser coagulation of the anastomoses addresses the cause of these transfusion imbalances. Besides transfusion imbalances, the monochorionic placenta may be unevenly divided, or one part may be dysfunctional, leading to an intertwin growth difference of more than 20%. Here, laser ablation of the anastomoses will usually not cure the problem but aims to protect the appropriately growing twin if the growth-restricted co-twin dies. In monochorionic twins, structural anomalies are twice as common as in singleton pregnancies, probably due to a teratogenic effect of the embryonic splitting or because of transfusion imbalances. In contrast, chromosomal anomalies appear less common, possibly because they more likely result in an early demise. Selective reduction is feasible in monochorionic pregnancies but carries increased risks of loss, miscarriage, and early birth than a selective reduction in a dichorionic setting. Finally, if one monochorionic twin dies spontaneously, its co-twin may acutely exsanguinate into the demised co-twin, which may result in the loss of both twins or brain damage in the surviving twin. This update addresses the pathophysiology, diagnosis, and management of these common complications in monochorionic diamniotic twin pregnancies.

Double Trouble: Complications in Twin Pregnancies

With the increasing rate of twin pregnancies due to increase in maternal age and use of assisted reproduction, it is important to be aware of unique diseases which occur specifically to twin pregnancies, especially in monochorionic twin pregnancies. These entities include twin to twin transfusion syndrome, twin anemia polycythemia sequence, twin reversed arterial perfusion, cotwin demise, and conjoined twins. Early evaluation and documentation are imperative to guide management which ultimately leads to better patient outcomes.

Twin to twin transfusion syndrome

Twin to twin transfusion syndrome (TTTS) is a common complication that typically presents in the second trimester of pregnancy in 10-15% of monochorionic twins due to net transfer of volume and hormonal substances from one twin to the other across vascular anastomoses on the placenta. Without recognition and treatment, TTTS is the greatest contributor to fetal loss prior to viability in 90-100% of advanced cases. Ultrasound diagnosis of monochorionicity is most reliable in the first trimester and sets the monitoring strategy for this type of twins. The diagnosis of TTTS is made by ultrasound with the findings of polyhydramnios due to volume overload and polyuria in one twin and oligohydramnios due to oliguria of the co-twin. Assessment of bladder filling as well as arterial and venous Doppler patterns are required for staging disease severity. Assessment of fetal cardiac function also provides additional insight into the fetal cardiovascular impacts of the disease as well as help identify fetuses that may require postnatal follow up. Fetoscopic laser ablation of the communicating vascular anastomoses between the twins is the standard treatment for TTTS. It aims to cure the condition by interrupting the link between their circulations and making them independent of one another. Contemporary outcome data after laser surgery suggests survival for both fetuses can be anticipated in up to 65% of cases and survival of a single fetus in up to 88% of cases. However, preterm birth remains a significant contributor to postnatal morbidity and mortality. Long term outcomes of TTTS survivors indicate that up to 11% of children may show signs of neurologic impairment. Strategies to minimize preterm birth after treatment and standardized reporting by laser centers are important considerations to improve overall outcomes and understand the long-term impacts of TTTS.

Pregnancy outcomes and placental characteristics of selective intrauterine growth restriction with or without twin anemia polythemia sequence

INTRODUCTION

To investigate differences in the pregnancy outcomes and placental characteristics of selective intrauterine growth restriction (sIUGR) with or without twin anemia polythemia sequence (TAPS).

METHODS

sIUGR patients were assigned into two groups based on the occurrence of TAPS. The pregnancy outcomes and placental characteristics were compared. A diameter of ≥2 mm was defined as thick anastomosis.

RESULTS

The prevalence of artery-to-artery (AA) (45.5% vs 88.6%, P = 0.002) and thick AA (0% vs 53.5%) in TAPS group were lower than non-TAPS group. The overall diameter of AA (0.5 (0.4-1.3) vs 2.5 (0.3-7.1) mm, P = 0.001) in TAPS group was smaller than non-TAPS group. The prevalence of thick artery-to-vein (AV) (0% vs 36.0%) in TAPS group was lower than non-TAPS group. Also, the overall diameter of AV (0.9 (0.6-2.1) vs 4.8 (0.3-17.8) mm, P < 0.001) in TAPS group was smaller than non-TAPS group. The total quantity (2 (1-6) vs 6 (1-16), P = 0.001), and the overall diameter of anastomoses (1.1 (0.6-4.7) vs 7.5 (0.5-22.4) mm, P < 0.001) were smaller in TAPS group than non-TAPS group. The placental territory discordance ratio of TAPS group was smaller than non-TAPS group (0.39 (0.13-0.56) vs 0.56 (0.01-0.88), P = 0.008). The umbilical cord insertion distance ratio in TAPS group was higher than non-TAPS group (0.81 ± 0.12 vs 0.57 ± 0.20, P < 0.001).

DISCUSSION

The placental anastomoses of sIUGR with TAPS were small. sIUGR with TAPS had smaller differences in placental share and larger distances between umbilical cord insertions.

Placental Anatomy and Function in Twin Gestations

With an increasing incidence of twin gestations, understanding the inherent risks associated with these pregnancies is essential in modern obstetrics. The unique differences in placentation in twins contribute to the increased risks. Monochorionic twins are susceptible to complications because of their unique placental architecture, including twin-to-twin transfusion syndrome, the twin anemia-polycythemia sequence, selective intrauterine growth restriction, and the twin reversed arterial perfusion sequence. Knowing the clinical correlations of placental anatomy in these gestations helps perinatal pathologists perform a more informed placental evaluation, allowing for better care for the mother and her children.

Longer distance between umbilical cord insertions is associated with spontaneous twin anemia polycythemia sequence

INTRODUCTION

The aim of the study was to investigate the placental characteristics in spontaneous twin anemia polycythemia sequence.

MATERIAL AND METHODS

A retrospective case-control study of spontaneous twin anemia polycythemia sequence, twin-to-twin transfusion syndrome and normal monochorionic diamniotic twin pregnancies was performed. The primary outcome was placental characteristics.

RESULTS

The prevalence of artery-artery anastomoses in spontaneous twin anemia polycythemia sequence and twin-to-twin transfusion syndrome groups was significantly lower than in the normal monochorionic diamniotic twin group (40.0% vs 33.3% vs 88.8%, respectively, P < .001). The total number of vascular anastomoses in the spontaneous twin anemia polycythemia sequence group (with range given in parentheses) was significantly lower than in the two control groups (3 [1-6] vs 5 [1-14] vs 6 [1-20], P = .001/<.001/.794). The number of artery-vein anastomoses in the spontaneous twin anemia polycythemia sequence was significantly lower than in the two control groups (2 [1-5] vs 4 [1-13] vs 5 [1-19], P = .011/.001/1.000). The total diameter of all vascular anastomoses was significantly smaller in the spontaneous twin anemia polycythemia sequence than in the two control groups (0.9 mm [0.3-4.7] vs 5.2 mm [0.8-24.6] vs 7.3 mm [1.0-25.1], P < .001/<.001/.104), as was the total diameter of artery-to-artery anastomoses (0.5 mm [0.3-1.3] vs 2.0 mm [0.5-11.8] vs 2.3 mm [0.7-9.7], P = .003/<.001/1.000) and the total diameter of artery-to-vein anastomoses (0.8 mm [0.3-2.1] vs 4.6 mm [0.8-15.3] vs 4.0 mm [0.2-21.8], P < .001/<.001/1.000). The ratio between the distance of the two umbilical cords insertion points and the placental maximum diameter in the spontaneous twin anemia polycythemia sequence group was significantly larger than in the two control groups (0.78 [0.49-0.99] vs 0.64 [0.32-1.00] vs 0.55 [0.05-1.00], P = .033/<.001/.138).

CONCLUSIONS

In spontaneous twin anemia polycythemia sequence placentas, the number of superficial vascular anastomoses is lower, their diameter is smaller and the distance between the two umbilical cord insertion points is longer.

US Evaluation of Twin Pregnancies: Importance of Chorionicity and Amnionicity

The twin birth rate is increasing in the United States. Twin pregnancies can be dichorionic or monochorionic (MC). MC twins account for 20% of twin pregnancies but 30% of all-cause pregnancy-related complications. This article describes the imaging findings that establish chorionicity and amnionicity. Ideally, these are established in the first trimester when accuracy is high, but they can also be determined later in pregnancy. Complications unique to MC twin pregnancy include twin-twin transfusion syndrome, twin anemia polycythemia sequence, twin reversed arterial perfusion sequence, and selective fetal growth restriction. The US features, staging systems, and management of these complications are reviewed, and the consequences of MC twin demise are illustrated. Ongoing surveillance for these conditions starts at 16 weeks gestation. Monoamniotic (MA) twins are a small subset of MC twins. In addition to all of the MC complications, specific MA complications include cord entanglement and conjoined twinning. Radiologists must be able to determine chorionicity and amnionicity and should be aware of potential complications so that patients may be referred to appropriate regional specialized centers. A proposed algorithm for referral to specialized fetal treatment centers is outlined. Online supplemental material is available for this article. ^©RSNA, 2019.

Middle Cerebral Artery Doppler Velocimetry for the Diagnosis of Twin Anemia Polycythemia Sequence: A Systematic Review

Twin anemia polycythemia sequence (TAPS) is a rare complication of monochorionic diamniotic (MCDA) twins. Middle cerebral artery peak systolic velocity (MCA-PSV) measurements are used to screen for TAPS while fetal or neonatal hemoglobin levels are required for definitive diagnosis. We sought to perform a systematic review of the efficacy of MCA-PSV in diagnosing TAPS. Search criteria were developed using relevant terms to query the Pubmed, Embase, and SCOPUS electronic databases. Publications reporting diagnostic characteristics of MCA-PSV measurements (i.e., sensitivity, specificity or receiver operator curves) were included. Each article was assessed for bias using the Quality Assessment of Diagnostic Accuracy Studies II (QUADAS II) tool. Results were assessed for uniformity to determine whether meta-analysis was feasible. Data were presented in tabular form. Among publications, five met the inclusion criteria. QUADAS II analysis revealed that four of the publications were highly likely to have bias in multiple areas. Meta-analysis was precluded by non-uniformity between definitions of TAPS by MCA-PSV and neonatal or fetal hemoglobin levels. High-quality prospective studies with consistent definitions and ultrasound surveillance protocols are still required to determine the efficacy of MCA-PSV in diagnosing TAPS. Other ultrasound findings (e.g., placenta echogenicity discordance) may augment Doppler studies.

Monochorionic diamniotic twins: What do I tell the prospective parents?

Monochorionic diamniotic twins occur in about 1 in 300 pregnancies. Compared with dichorionic twins, they face increased risks because of the shared circulation. In about 15%, an imbalance in blood exchange occurs, such as twin-twin transfusion syndrome and twin anemia polycythemia sequence. In this review, we summarize the latest evidence on the management of monochorionic diamniotic twin pregnancies and their specific complications, with a focus on information that is relevant for prospective parents.

Twin-twin transfusion syndrome in the era of fetoscopic laser surgery: antenatal management, neonatal outcome and beyond

Introduction: Twin-twin transfusion syndrome (TTTS) is a devastating complication of monochorionic twin pregnancy and remains a major challenge for worldwide fetal medicine specialists. In TTTS, intertwin transfusion through vascular anastomoses in the shared placenta leads to severe hemodynamic imbalance. This review summarizes the current knowledge of TTTS.Areas covered: The most recent insights concerning the management of TTTS, as well as fetal and neonatal complications are described. Relevant articles were selected based on a Pubmed search using the keywords below. Understanding of the underlying pathophysiology has improved greatly as a result of placental injection studies. Advancements in antenatal management have led to increased perinatal survival and a decreased incidence of neonatal complications, including brain injury and neurodevelopmental impairment.Expert opinion: Further opportunities for improvement comprise technological innovations in laser procedures and the prevention of preterm rupture of membranes with subsequent prematurity. A noninvasive treatment such as high-intensity focused ultrasound (HIFU) seems to hold promise for the future treatment of TTTS. Fetal MRI studies are important to improve our understanding of fetal brain injury and should relate their findings to long-term neurodevelopment. International collaboration and centralization of care are of paramount importance to ensure the best care for our patients.

Complex multigestational anomalies

The increase in multiple gestation pregnancies has resulted in significant health care implications for both mother and child. Our ability to diagnose and intervene on an at-risk multi-gestation pregnancy has dramatically improved. It is important for the pediatric surgeon to be equipped with a basic fund of knowledge concerning these pregnancies. An understanding of amnionicity and chorionicity will equip the practitioner with the ability to identify which pregnancies are at risk for specific complications. This article highlights multi-gestation pregnancies that are monochorionic (single shared placenta) and can be complicated by twin-twin transfusion syndrome (TTTS), twin reversed arterial perfusion (TRAP) sequence, twin anemia polycythemia sequence (TAPS), or selective fetal intrauterine growth restriction (sIUGR). The risk of fetal demise is significant in these pregnancies. Understanding recommended surveillance and warning signs can alert surgeons to developing complications. Specialized fetal care centers possess the ability to intervene on these pregnancies in utero.

Twin anemia-polycythemia sequence and routine monitoring practices amongst maternal-fetal medicine specialists in the United States: an initial investigation

Background The purpose of this initial investigation was to begin to understand the routine twin anemia-polycythemia sequence (TAPS) monitoring practices of maternal-fetal medicine specialists (MFM specialists) in the United States in the absence of a formal guideline. Methods This study used an anonymous, online survey of 90 MFM specialists who were practicing in the United States. A $5 gift card to an online store was used to incentivize participants. Descriptive statistics were calculated. Results All MFM specialists reported at least some familiarity (100.00%) with TAPS. Most participants (92.94%) were familiar with methods for monitoring patients for TAPS and nearly all (97.50%) responded that they use 'Doppler MCA-PSV' to make a prenatal TAPS diagnosis. Nearly two-thirds of MFM specialists surveyed (65.06%) reported performing regular TAPS monitoring for patients with monochorionic-diamniotic (MCDA) pregnancies. Conclusion Despite no formal guidelines, the majority of American MFM specialists surveyed are using routine TAPS screening in their management of MCDA twin pregnancies, suggesting that the MFM specialists included in this study consider it a valuable diagnostic tool. Future research should further explore this possible trend toward routine TAPS monitoring amongst MFM specialists in the United States, as well as the potential value of routine TAPS monitoring in MCDA pregnancy.

Severe gyration and migration disorder in fetofetal transfusion syndrome: two case reports and a review of the literature on the neurological outcome of children with lesions on neuroimaging

INTRODUCTION

Fetofetal transfusion syndrome is a dreaded cause of morbidity and mortality in monochorionic pregnancies.

CASE REPORTS

We present two pairs of twins one of which we have followed for more than 6 years. The donors suffer from cerebral palsy, orofacial, and motor problems, and both are significantly smaller than their recipient twins. Interestingly, cranial MRI revealed medial frontal lobe polymicrogyria, ventriculomegaly, and decreased thickness in both parietal lobes in both donors. We suggest this as a possible feature of fetofetal transfusion syndrome.

REVIEW

A minireview of the literature on neuroimaging and neurodevelopmental outcome in fetofetal transfusion syndrome is presented.

CONCLUSION

While the close resemblance of the imaging features of both cases is likely incidental further study of a connection between migration and gyration disorders and fetofetal transfusion syndrome is warranted.

Redness discordance in monochorionic twin placentas: Correlation with clinical and placental findings

INTRODUCTION/OBJECTIVES

Recent studies suggest redness (color) discordance of the placental basal plate may be a marker for twin anemia-polycythemia sequence (TAPS), a recently described complication of diamniotic-monochorionic twinning characterized by marked intertwin hemoglobin (Hb) discordance in the absence of oligohydramnios-polyhydramnios. In this study, we determined the clinicoplacental and choriovascular correlates of basal plate color discordance in monochorionic twin placentas, and assessed its value as postnatal indicator of TAPS.

METHODS

We performed a clinicoplacental analysis of 100 consecutive non-TTTS diamniotic-monochorionic twin placentas with available photographic documentation of the basal plate. Basal plate redness was quantified by computer-assisted analysis of digital images and expressed as intertwin color difference ratio (CDR).

RESULTS

The CDR ranged between 1.00 and 3.58 (median CDR: 1.14; 90^th %ile: 1.98). Compared to twins with low CDR (N = 90), twins with high CDR (≥2.0; N = 10) had significantly higher hemoglobin difference (11.25 g/dL versus 2.55 g/dL) and significantly fewer and smaller artery-to-artery (AA) and artery-to-vein (AV) anastomoses. Apgar scores and birth weights were equivalent in both groups. Among the 10 twin sets with high CDR, six (60%) qualified as TAPS, as defined by intertwin Hb difference >8 g/dL and absent or very small AA and AV anastomoses. Conversely, 6 of 8 (75%) twin sets with TAPS had a CDR ≥ 2.0.

CONCLUSION

Intertwin CDR correlates with intertwin hemoglobin difference and chorionic angioarchitecture. A CDR value ≥ 2.0 (the 90%ile value for CDR derived from the present cohort) has high specificity (96%), but relatively low positive predictive value (60%) as indicator of TAPS, as currently defined.

Intrauterine fetal death in triplet gestation caused by feto-fetal transfusion syndrome - a case report

Feto-fetal transfusion syndrome (FFTS) severely affects monochorionic (MC) multiple pregnancies and affects 1 in 1600 pregnancies overall. The number of increasing disputed obstetrics cases in China is related to unavailability of prompt diagnosis of FFTS. We present here a woman with a MC triplet pregnancy with intrauterine fetal death at 33 weeks of gestation due to FFTS. Subsequent pathological anatomy showed that the MC placenta contained vascular anastomoses, including arterio-arterial anastomosis and arterio-venous anastomosis. These anastomoses led to unidirectional blood flow with the absence of adequate compensatory counter-transfusion and bi-directional flow. When encountering such challenging conditions, medical practitioners should discreetly compare the fetuses' characteristics with features of placental blood vessels and consult morphological and pathological findings. Furthermore, they should perform ultrasound examinations, particularly focussing on fetal size differences and the maximum vertical pocket in the diagnosis of FFTS, especially in MC multiple pregnancies with abdominal symptoms.

Twin-twin transfusion and laser therapy

PURPOSE OF REVIEW

Twin-to-twin transfusion syndrome (TTTS) is an uncommon, but dangerous, complication of monochorionic diamniotic twin gestations. The purpose of this review is to provide an update on the evolving treatments in TTTS as it pertains primarily to laser photocoagulation, as well as to provide recently published information on outcomes.

RECENT FINDINGS

The Solomon laser technique, in which selective fetoscopic laser photocoagulation is first performed and then followed by laser of the vascular equator from one side of the placenta to the other, reduces TTTS complications of twin anemia-polycythemia syndrome and recurrent TTTS. The addition of fetal echocardiography to the historical staging of TTTS adds important information that may guide future therapies. The postlaser ablation rate of neurodevelopmental delay in TTTS has recently been reported to be 14%. Cotwin demise is a significant complication of untreated TTTS and survival carries a 25% risk of cystic periventricular leukomalacia, middle cerebral artery infarction, and injury to other central nervous system structures as noted by neuroimaging.

SUMMARY

Laser therapy for TTTS is clearly the only therapy that halts the disease process, allows both fetuses an opportunity to survive and protects a surviving cotwin in the event of the demise of one twin. Laser techniques have evolved greatly over the last 25 years and recent reports with the addition of the Solomon technique appearing to reduce some postlaser complications (twin anemia-polycythemia sequence and recurrent TTTS). Future focus of TTTS therapy should be centered on understanding the pathophysiology of the disease better with improvement in staging of the disease and on comparison of different laser techniques with the overall goal of not only increasing twin survival rates but also reducing long term neurodevelopmental morbidity.

Can middle cerebral artery peak systolic velocity predict polycythemia in monochorionic-diamniotic twins? Evidence from a prospective cohort study

OBJECTIVE

The antenatal diagnosis of twin anemia-polycythemia sequence (TAPS) in monochorionic-diamniotic (MCDA) twin pregnancies is based on elevated peak systolic velocity in the middle cerebral artery (MCA-PSV) in the donor twin and decreased MCA-PSV in the recipient twin. However, the association between these parameters and polycythemia has not yet been established. The aim of this study was to determine whether MCA-PSV can predict polycythemia in MCDA pregnancies.

METHODS

This was a prospective cohort study of MCDA pregnancies recruited at 14-18 weeks' gestation from a single tertiary care center between January 2011 and June 2014. Fetal MCA Doppler waveforms were recorded every 2 weeks from 18 weeks' gestation until delivery. Only those with an MCA-PSV measurement within 1 week of delivery were included in the analysis. Neonatal hematocrit level was determined in all twins from venous blood obtained within 4 h of delivery. Polycythemia was defined as a hematocrit of > 65%, and anemia as a hematocrit of < 45%. TAPS was diagnosed when an intertwin hemoglobin difference of > 8 g/dL and reticulocyte count ratio of > 1.7 were observed.

RESULTS

Of 162 MCDA pregnancies followed during the study period, 69 had an MCA-PSV measurement within 1 week of delivery and were included in the study. Twenty-five neonates were diagnosed with polycythemia and nine twin pairs met the criteria for TAPS. In a pooled analysis, MCA-PSV was negatively correlated with neonatal hematocrit (P = 0.017, r = -0.215) and was significantly higher in anemic fetuses than in normal controls (1.15 multiples of the median (MoM) vs 1.02 MoM, respectively; P = 0.001). However, MCA-PSV was similar among polycythemic and normal fetuses (0.95 MoM vs 1.02 MoM, respectively; P = 0.47). Intertwin difference in MCA-PSV (delta MCA-PSV) was positively correlated with intertwin hematocrit difference (P = 0.002, r = 0.394). Moreover, twin pregnancies with an intertwin hematocrit difference of > 24% had a significantly greater delta MCA-PSV than did those with an intertwin hematocrit difference of ≤ 24% (delta MCA-PSV, 19 vs 5 cm/s; P < 0.001).

CONCLUSIONS

MCA-PSV is not significantly decreased in polycythemic MCDA twins. However, delta MCA-PSV is associated with a large intertwin difference in hematocrit, and its use may be better than conventional methods for the risk assessment of TAPS. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Twin Anemia Polycythemia Sequence: Current Views on Pathogenesis, Diagnostic Criteria, Perinatal Management, and Outcome

Monochorionic twins share a single placenta and are connected with each other through vascular anastomoses. Unbalanced inter-twin blood transfusion may lead to various complications, including twin-to-twin transfusion syndrome (TTTS) and twin anemia polycythemia sequence (TAPS). TAPS was first described less than a decade ago, and the pathogenesis of TAPS results from slow blood transfusion from donor to recipient through a few minuscule vascular anastomoses. This gradually leads to anemia in the donor and polycythemia in the recipient, in the absence of twin oligo-polyhydramnios sequence (TOPS). TAPS may occur spontaneously in 3-5% of monochorionic twins or after laser surgery for TTTS. The prevalence of post-laser TAPS varies from 2% to 16% of TTTS cases, depending on the rate of residual anastomoses. Pre-natal diagnosis of TAPS is currently based on discordant measurements of the middle cerebral artery peak systolic velocity (MCA-PSV; >1.5 multiples of the median [MoM] in donors and 8 g/dL), and at least one of the following: reticulocyte count ratio >1.7 or minuscule placental anastomoses. Management includes expectant management, and intra-uterine blood transfusion (IUT) with or without partial exchange transfusion (PET) or fetoscopic laser surgery. Post-laser TAPS can be prevented by using the Solomon laser surgery technique. Short-term neonatal outcome ranges from isolated inter-twin Hb differences to severe neonatal morbidity and neonatal death. Long-term neonatal outcome in post-laser TAPS is comparable with long-term outcome after treated TTTS. This review summarizes the current knowledge after 10 years of research on the pathogenesis, diagnosis, management, and outcome in TAPS.

Fetal cardiovascular hemodynamics in twin-twin transfusion syndrome

Twin-twin transfusion syndrome (TTTS) complicates 10-15% of monochorionic-diamniotic (MCDA) pregnancies. It originates from unbalanced transfer of fluid and vasoactive mediators from one twin to its co-twin via placental anastomoses. This results in hypovolemia in the donor and hypervolemia and vasoconstriction in the recipient twin. Consequently, the recipient demonstrates cardiovascular alterations including atrioventricular valve regurgitation, diastolic dysfunction, and pulmonary stenosis/atresia that do not necessarily correlate with Quintero-stages. Selective fetoscopic laser photocoagulation of placental vascular anastomoses disrupts the underlying pathophysiology and usually improves cardiovascular function in the recipient with normalization of systolic and diastolic function within weeks after treatment. Postnatal studies have demonstrated early decreased arterial distensibility in ex-donor twins, but 10-year follow up is encouraging with survivors showing normal cardiovascular function after TTTS. However, prediction and appropriate early management of TTTS remain poor. Assessment of the cardiovascular system provides additional insight into the pathophysiology and severity of TTTS and may permit more targeted early surveillance of MCDA pregnancies in future. It should form an integral part of the diagnostic algorithm.

Does anemia-polycythemia complicating twin-twin transfusion syndrome affect outcome after fetoscopic laser surgery?

OBJECTIVE

Twin anemia-polycythemia sequence (TAPS) can occur as a unique disease or as a complication of twin-twin transfusion syndrome (TTTS). Middle cerebral artery (MCA) Doppler studies are not currently part of the routine evaluation of monochorionic twins since they are not used in the Quintero staging system. As such, the true incidence of TAPS is unknown. We aimed to compare the characteristics and outcomes of twin pregnancies with TTTS complicated by spontaneous anemia-polycythemia vs those with TTTS alone.

METHODS

This was a secondary analysis of data collected prospectively from a cohort of 156 consecutive patients undergoing fetoscopic laser surgery for TTTS, between October 2011 and August 2014. TAPS was defined as discordance in the preoperative MCA peak systolic velocity (PSV), with one twin fetus having MCA-PSV ≤ 1.0 multiples of the median (MoM) and the other having MCA-PSV ≥ 1.5 MoM. Maternal demographics as well as preoperative, operative and postoperative variables were analyzed.

RESULTS

Included in the final analysis were 133 patients with complete records: 11 cases with TTTS with anemia-polycythemia and 122 cases with TTTS alone. There was no difference in maternal body mass index, gestational age (GA) at procedure, rate of preterm prelabor rupture of membranes or GA at delivery between the two groups. Patients with TTTS and anemia-polycythemia were more likely to be older (P = 0.03) and parous (P = 0.04) and had a significantly lower number of placental anastomoses (P = 0.01). The dual live-birth rate was similar for both groups (P = 0.76).

CONCLUSION

Cases of TTTS with anemia-polycythemia were more likely to be found in parous and older women and were characterized by fewer vascular anastomoses. TTTS with anemia-polycythemia was not associated with worse perinatal outcome after laser therapy. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Twin Anemia-Polycythemia Sequence: Perinatal Management and Outcome

Objective: To determine the perinatal outcome of monochorionic twin pregnancies complicated by twin anemia-polycythemia sequence (TAPS). Methods: All monochorionic twins diagnosed with TAPS between 2011 and 2014 were included. Each twin pair with TAPS (study group) was compared with 2 uncomplicated monochorionic twin pairs who were matched for gestational age at delivery (control group). Neonatal morbidity and mortality were evaluated. Results: During the study period, 179 monochorionic twins were followed at our center, of whom 46 underwent laser ablation due to twin-to-twin transfusion syndrome. TAPS was diagnosed in 10 cases; 8 of them were spontaneous, and 2 occurred following laser surgery. Out of 7 patients diagnosed prenatally with TAPS, 5 cases were managed expectantly, and 2 cases were treated with intrauterine blood transfusion. The rates of severe and mild central nervous system lesions on postnatal ultrasound were similar in the TAPS group and control group (5.0 vs. 2.5%, p = 0.61, and 5.0 vs. 12.5%, p = 0.25, respectively). Additionally, severe neonatal morbidity was comparable between the groups. All neonates were alive at 1 month of age. Conclusion: The neonatal outcome of monocohorionic twins affected by TAPS is favorable and comparable to gestational age-matched uncomplicated monochorionic twins.

The North American Fetal Therapy Network Consensus Statement: Management of Complicated Monochorionic Gestations

The North American Fetal Therapy Network is a consortium of 30 medical institutions in the United States and Canada with established expertise in fetal therapy and other forms of multidisciplinary care for complex fetal disorders. This publication is the third in a series of articles written by NAFTNet about monochorionic pregnancies. In this article, we provide the general obstetric practitioner with information regarding management options available for complications of monochorionic gestations. This information may be useful for a better understanding of the pathophysiology of the various conditions, for better patient counseling, for timely referral to a regional treatment center, and for ongoing comanagement after treatment.

Society for Maternal-Fetal Medicine (SMFM) Clinical Guideline #8: the fetus at risk for anemia--diagnosis and management

OBJECTIVE

We sought to provide evidence-based guidelines for the diagnosis and management of fetal anemia.

METHODS

A systematic literature review was performed using MEDLINE, PubMed, EMBASE, and the Cochrane Library. The search was restricted to English-language articles published from 1966 through May 2014. Priority was given to articles reporting original research, in particular randomized controlled trials, although review articles and commentaries were consulted. Abstracts of research presented at symposia and scientific conferences were not considered adequate for inclusion. Evidence reports and published guidelines were also reviewed, and additional studies were located by reviewing bibliographies of identified articles. GRADE (Grading of Recommendations Assessment, Development, and Evaluation) methodology was used for defining the strength of recommendations and rating the quality of evidence. Consistent with US Preventive Task Force guidelines, references were evaluated for quality based on the highest level of evidence.

RESULTS AND RECOMMENDATIONS

We recommend the following: (1) middle cerebral artery peak systolic velocity (MCA-PSV) measured by ultrasound Doppler interrogation be used as the primary technique to detect fetal anemia; (2) amniotic fluid delta OD450 not be used to diagnosis fetal anemia; (3) MCA-PSV assessment be reserved for those patients who are at risk of having an anemic fetus (proper technique for MCA-PSV evaluation includes assessment of the middle cerebral artery close to its origin, ideally at a zero degree angle without angle correction); (4) if a fetus is deemed at significant risk for severe fetal anemia (MCA greater than 1.5 multiples of the median or hydropic), fetal blood sampling be performed with preparation for an intrauterine transfusion, unless the pregnancy is at a gestational age when the risks associated with delivery are considered to be less than those associated with the procedure; (5) if a fetus is deemed at significant risk for severe fetal anemia, the patient be referred to a center with expertise in invasive fetal therapy; (6) MCA-PSV be considered to determine the timing of a second transfusion in fetuses with anemia, and, alternatively, a predicted decline in fetal hemoglobin may be used for timing the second procedure; and (7) pregnancies with a fetus at significant risk for fetal anemia be delivered at 37-38 weeks of gestation unless indications develop prior to this time.

Evaluation of the Utility of in utero Treatment of Twin Anemia-Polycythemia Sequence

OBJECTIVE

The aim of this study is to evaluate the interest in the in utero treatment of twin anemia-polycythemia sequence (TAPS).

METHODS

The obstetrical and neonatal data on all cases of TAPS followed up in our institution between 2006 and 2013 were reviewed. Statistical analyses were conducted using Bayesian methods.

RESULTS

Twenty cases of TAPS were included. Laser therapy or intrauterine transfusion (IUT) was performed on the donor twin in 9 cases. Eleven cases were included in the 'nontreated' group (managed expectantly or diagnosed at birth). The gestational age at diagnosis was lower in the group with treated TAPS [difference (diff) = -22.20 days (-57.13, 14.28), probability (Pr) (diff >0) = 10.6%]. The rate of preterm premature rupture of membranes was higher in the group with treated TAPS [diff = 22.5% (-14, 57), Pr (diff >0) = 89%], but overall mortality was similar. The interval between diagnosis and delivery was longer [diff = 44.37 days (9.41, 77.90), Pr (diff >0) = 99.2%], the TAPS resolution rate was higher [diff = 49.9% (12, 81), Pr (diff >0) = 99.4%], and the neonatal transfusion rate was lower [diff = -30.5% (-60, 0), Pr (diff >0) = 2.6%] in the treated group.

CONCLUSION

In utero treatment for TAPS is associated with a higher resolution rate of TAPS and a longer time between diagnosis and birth, but overall mortality is the same as with expectant management.

The North American Fetal Therapy Network consensus statement: prenatal surveillance of uncomplicated monochorionic gestations

Because they share a common placenta, monochorionic gestations are subject to unique pregnancy complications that can threaten the life and health of both fetuses and therefore impose a disproportionate disease burden on overall perinatal morbidity and mortality. Early detection of these unique disease processes may allow for prompt referral to a regional treatment center, comprehensive counseling, and better patient outcomes. The North American Fetal Therapy Network is a consortium of 30 medical institutions in the United States and Canada with established expertise in fetal surgery and other forms of multidisciplinary care for complex fetal disorders. The goal of this publication is to briefly describe complications of monochorionic gestations and to provide multidisciplinary, evidence-based, and consensus-driven recommendations for surveillance of uncomplicated monochorionic gestations.

Pre-Operative Twin Anemia/Polycythemia in the Setting of Twin-Twin Transfusion Syndrome (TTTS)

Introduction: Twin-twin transfusion syndrome (TTTS) and twin anemia-polycythemia sequence (TAPS) are classified as distinct clinical disorders associated with unbalanced blood flow through placental vascular communications. Typically, TAPS placentas demonstrate few <1 mm arteriovenous (AV) communications, and at fetoscopy the twins are visibly pale and plethoric. Materials and Methods: In a cohort of TTTS patients who underwent laser surgery, those with preoperative findings suggestive of anemia/polycythemia (AP) were compared to those with TTTS alone. AP was defined as middle cerebral artery peak systolic velocity in one twin >1.5 multiples of the median (MoM), and <1.0 MoM in the other. Results: Of 369 TTTS patients, 9 (2.4%) met criteria for preoperative AP. The mean number (±SD) of AV communications in the TTTS + AP group was 5.6 ± 5.7, compared with 8.8 ± 4.8 in the TTTS-alone group (p = 0.013). Five TTTS + AP patients (56%) had a few thin AV communications (mean 2.8 ± 1.6); all 5 had visibly pale and plethoric twins. The remaining 4 (44%) had large or numerous anastomoses (mean 10.5 ± 6.8); none had fetal skin color discordance. Discussion: Preoperative AP affected 2% of TTTS patients. Of these, approximately half had placental and skin color findings typically reported with isolated TAPS.

Fetal surgery: principles, indications, and evidence

Since the first human fetal surgery was reported in 1965, several different fetal surgical procedures have been developed and perfected, resulting in significantly improved outcomes for many fetuses. The currently accepted list of fetal conditions for which antenatal surgery is considered include lower urinary tract obstruction, twin-twin transfusion syndrome, myelomeningocele, congenital diaphragmatic hernia, neck masses occluding the trachea, and tumors such as congenital cystic adenomatoid malformation or sacrococcygeal teratoma when associated with developing fetal hydrops. Until recently, it has been difficult to determine the true benefits of several fetal surgeries because outcomes were reported as uncontrolled case series. However, several prospective randomized trials have been attempted and others are ongoing, supporting a more evidence-based approach to antenatal intervention. Problems that have yet to be completely overcome include the inability to identify ideal fetal candidates for antenatal intervention, to determine the optimal timing of intervention, and to prevent preterm birth after fetal surgery. Confronting a fetal abnormality raises unique and complex issues for the family. For this reason, in addition to a maternal-fetal medicine specialist experienced in prenatal diagnosis, a pediatric surgeon, an experienced operating room team including a knowledgeable anesthesiologist, and a neonatologist, the family considering fetal surgery should have access to psychosocial support and a bioethicist.

Examination of the twin placenta

Twin birth rates have increased dramatically over the past three decades, and twins currently account for 3% of all pregnancies. Twin pregnancies of any type are at risk for prematurity. In addition, monochorionic twin pregnancies (25-30% of all twin pregnancies) are predisposed to a specific set of complications, including twin-to-twin transfusion syndrome (TTTS), twin reversed arterial perfusion syndrome (TRAP), malformations, and intertwin growth discordance. This article reviews the basic mechanisms underlying the twinning process, the relationship between zygosity and chorionicity, and the various types of twinning. We describe the major complications of monochorionic twinning in association with their reported placental characteristics (or lack thereof). Finally, a rational, evidence-based approach to examination of the twin placenta is presented. It is essential for the pathologist to understand the value, strengths, and limitations of examination of the twin placenta in order to provide a meaningful clinicopathological correlation in complicated (monochorionic) twin pregnancies.

Residual anastomoses in twin-twin transfusion syndrome after laser: the Solomon randomized trial

OBJECTIVE

Residual anastomoses after fetoscopic laser surgery for twin-to-twin transfusion syndrome (TTTS) may lead to severe postoperative complications, including recurrent TTTS and twin anemia-polycythemia sequence (TAPS). A novel technique (Solomon technique) using laser coagulation of the entire vascular equator was recently investigated in a randomized controlled trial (Solomon trial) and compared with the Standard selective laser technique. The aim of this secondary analysis was to evaluate the occurrence and characteristics of residual anastomoses in placentas included in the Solomon trial.

STUDY DESIGN

International multicenter randomized controlled trial in TTTS, randomized 1:1 ratio to either the Solomon laser technique or Standard laser technique. At time of laser, surgeons recorded whether they considered the procedure to be complete. Placental dye injection was performed after birth in the participating centers to evaluate the presence of residual anastomoses.

RESULTS

A total of 151 placentas were included in the study. The percentage of placentas with residual anastomoses in the Solomon group and Standard group was 19% (14/74) and 34% (26/77), respectively (P = .04). The percentage of placentas with residual anastomoses in the subgroup of cases where the procedure was recorded as complete was 8/65 (12%) and 22/69 (32%) in the Solomon group and Standard group, respectively (P < .01).

CONCLUSION

The Solomon laser technique reduces the risk of residual anastomoses. However, careful follow-up remains essential also after the Solomon technique, as complete dichorionization is not always achieved.