The impact of placental anastomoses and umbilical cord insertions' sites on monochorionic twin pregnancy outcomes: Evidence from color-dye injection studies

INTRODUCTION

Our knowledge of monochorionic pregnancies' complications is largely based on the extensive ongoing research on monochorionic placental structure. Previous studies on the concordance of umbilical cord insertions are limited. This study aimed to evaluate placental anastomoses and cord insertions as independent risk factors for neonatal adverse outcomes.

METHODS

This was a prospective study conducted at Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy from April 2021 to December 2022. Seventy-six women with a monochorionic pregnancy were enrolled at their first-trimester scan. After delivery, all placentas that were confirmed to be monochorionic were analyzed according to standard protocols, including those of complicated monochorionic twin pregnancies. The primary outcomes were a Composite Monochorionic Pregnancy Outcome (CMPO) and a Composite Neonatal Adverse Outcome (CNAO). The secondary outcome was the birth weight discordance between the neonates.

RESULTS

The CMPO occurred in 15.8 % pregnancies, and the CNAO occurred in 67.1 % pregnancies. The analysis confirmed a significant association between velamentous cord insertions and neonatal adverse events (p = 0.003). Also, a significant positive association (p = 0.0326) between twin birth weight discordance and discordance in twins umbilical cord insertions' sites was found. No significant association between the number and type of the anastomoses and both the CMPO or CNAO was detected.

DISCUSSION

Our data suggest that the routine sonographic assessment of umbilical cords' insertion sites during the first trimester could be helpful in predicting fetal and neonatal adverse events. We believe that this sonographic assessment should start to be implemented in our routine care of monochorionic pregnancies.

Significance of placental cord insertion site in twin pregnancy

OBJECTIVE

To investigate the association between abnormal cord insertion and the development of twin-specific complications, including birth-weight discordance, selective fetal growth restriction (sFGR) and twin-to-twin transfusion syndrome (TTTS).

METHODS

This was a single center retrospective cohort study of twin pregnancies. Abnormal cord insertion was defined as either marginal (umbilical cord attachment site less than 2 cm to the nearest margin of the placental disc) or velamentous (cord attached to the membrane before reaching the placental disc with clear evidence of vessels traversing the membranes to connect with the placental disc), as described in placental pathology reports. Twins with major structural or chromosomal abnormalities and monochorionic monoamniotic twins were not included in the study. Information on the pregnancies, ultrasound findings, prenatal investigations and interventions was obtained from the electronic ultrasound database, while data on placental histopathological findings, pregnancy outcome, mode of delivery, birth weight, gestational age at delivery and admission to the neonatal intensive care unit were obtained from maternity records. Categorical variables were compared using the chi-square or Fisher's exact test, while continuous variables were compared using the Student's t-test, ANOVA for multiple comparisons and the Kruskal-Wallis test.

RESULTS

Of the 497 twin pregnancies included in the analysis, 351 (70.6%) were dichorionic and 146 (29.4%) were monochorionic. The incidence of birth-weight discordance of 25% or more was significantly higher in pregnancies with velamentous and those with marginal cord insertions compared to those with normal cord insertion (24.0%, 15.3% vs 7.6%, P < 0.001 and P = 0.020, respectively). In pregnancies with birth-weight discordance of 25% or more, the smaller twins had significantly higher prevalence of velamentous (13.8%) and marginal (34.2%) cord insertions compared with the larger twins (1.8% and 18.5%, respectively, P < 0.001). The smaller twins of the monochorionic diamniotic pregnancies showed an even higher prevalence of velamentous (29.5%) and marginal (40.9%) cord insertions compared with the larger twins (2.3% and 31.5%, respectively, P < 0.001). Compared with the normal cord insertion group, only velamentous insertion was associated significantly with the risk of sFGR (odds ratio (OR), 9.24 (95% CI, 2.05-58.84), P < 0.001) and birth-weight discordance of 20% or more (OR, 4.34 (95% CI, 1.36-14.61), P = 0.007) and 25% or more (OR, 6.81 (95% CI, 1.67-34.12), P = 0.003) in monochorionic twin pregnancies. There was no significant association between velamentous cord insertion and TTTS (P = 0.591), or between marginal cord insertion and the development of sFGR (P = 0.233), birth-weight discordance of 25% or more (P = 0.114) or TTTS (P = 0.487). Subgroup analysis of dichorionic twins showed that abnormal cord insertion was not associated with the risk of birth-weight discordance (P = 0.999), sFGR (P = 0.308), composite neonatal adverse outcome (P = 0.637) or intrauterine death (P = 0.349).

CONCLUSION

Monochorionic twins with velamentous cord insertion are at increased risk of birth-weight discordance and sFGR. Sonographic delineation of placental cord insertion could be of value in the antenatal stratification of twin pregnancies. Prospective studies are required to assess the value and predictive accuracy of this potential screening marker. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Does site of cord insertion increase risk of adverse outcome, twin-to-twin transfusion syndrome and discordant growth in monochorionic twin pregnancy?

OBJECTIVES

It is not currently well known to what extent the sites of cord insertion influence the risk of complicated outcome in monochorionic twin pregnancy. The objectives of this study were to examine whether the sites of cord insertion, as determined on prenatal ultrasound examination, affect the risks of adverse outcome, twin-to-twin transfusion syndrome (TTTS) and discordant growth, and whether discordance in insertion sites or velamentous insertion in one or both twins best predicts risk.

METHODS

This was a retrospective cohort study of monochorionic diamniotic twin pregnancies followed from the first trimester. The cohort was divided into three groups of increasing discordance in cord insertion sites: concordant (normal-normal; marginal-marginal; velamentous-velamentous), intermediate (normal-marginal; marginal-velamentous) and discordant (normal-velamentous). Adverse outcome was defined as fetal or neonatal loss or birth prior to 32 weeks. The associations of adverse outcome, TTTS and discordant growth were assessed using logistic regression analysis with the following predictors: the three groups of insertion sites and velamentous insertion in one or both twins.

RESULTS

Included in the analysis were 518 pregnancies. On univariate analysis, both discordant and velamentous insertions in one twin increased the risk of adverse outcome, TTTS and discordant growth. Intermediate insertion only increased the risk of discordant growth. Velamentous insertion in both twins increased the risk of adverse outcome and TTTS, but not of discordant growth. Multivariate logistic regression analysis showed velamentous insertion in one or both twins to independently predict adverse outcome and TTTS. For discordant growth, both intermediate/discordant and velamentous cord insertion in one twin were independent predictors.

CONCLUSIONS

Velamentous cord insertion in one or both twins increases the risk of adverse outcome and TTTS, irrespective of discordance in the insertion sites, whereas the risk of discordant growth is determined by both discordance in insertion sites and velamentous cord insertion in one twin. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Chorioamniotic membrane separation after fetoscopy in monochorionic twin pregnancy: incidence and impact on perinatal outcome

OBJECTIVE

To evaluate the incidence of chorioamniotic membrane separation (CMS) after fetoscopy in monochorionic diamniotic (MCDA) twins and its impact on pregnancy outcome.

METHODS

The study group comprised a consecutive series of 338 women with an MCDA pregnancy complicated by twin-twin transfusion syndrome (TTTS) or selective intrauterine growth restriction (sIUGR) treated with selective laser photocoagulation of communicating vessels (SLPCV) or cord occlusion (CO). Data obtained included cervical length, gestational age at procedure, type and duration of surgery and placental location. The incidence of CMS, the rates of miscarriage and preterm prelabor rupture of membranes (PPROM), gestational age at delivery and neonatal survival were recorded.

RESULTS

Of the study population of MCDA pregnancies, 270 (79.9%) had TTTS and 68 (20.1%) had sIUGR. SLPCV was performed in 252 (74.6%) cases and CO in 86 (25.4%). Postoperative CMS was observed in 70 (20.7%) cases. Patients with CMS had higher rates of miscarriage (14.3% vs 7.1%; P = 0.049), PPROM before 32 weeks (43.3% vs 13.7%; P < 0.001) and preterm delivery before 32 weeks (53.3% vs 26.1%; P < 0.001) and a lower rate of neonatal survival of at least one twin (81.7% vs 93.6%; P = 0.003). Multivariate analysis showed that gestational age at surgery was the only independent predictor, with the highest proportion of CMS occurring in cases that underwent surgery before 18 weeks' gestation (odds ratio, 2.941 (95% CI, 1.640-5.275); P < 0.001). There was no influence of cervical length, placental location, duration of surgery or type of surgery on the risk of CMS.

CONCLUSIONS

CMS complicated one-fifth of all MCDA pregnancies that underwent fetoscopy. It appeared to be more common in those who underwent surgery before 18 weeks' gestation and was associated with poorer outcomes. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Midtrimester isolated polyhydramnios in monochorionic diamniotic multiple gestations

OBJECTIVE

To identify risk factors for development of twin-twin transfusion syndrome (TTTS) in monochorionic diamniotic multiple gestations complicated by midtrimester isolated polyhydramnios (iPoly).

STUDY DESIGN

A retrospective study of patients referred for possible TTTS between 16 and 26 gestational weeks was performed. IPoly was defined as a maximum vertical pocket of ≥8 cm in the iPoly twin's sac and >2 and <8 cm in the co-twin's sac on the consultative ultrasound.

RESULTS

Of 628 consecutive patients referred for possible TTTS, 74 were diagnosed with iPoly. The majority of these patients (n = 52, 70.3%) were not subsequently diagnosed with TTTS, and of these, 40 were managed expectantly and 12 had amnioreductions because of symptomatic iPoly; 30-day perinatal survival of at-least-one twin in the non-TTTS group was 93.0% (40/43). TTTS developed in the 22 remaining patients, of which 63.6% were of advanced Quintero Stage. Nineteen underwent laser surgery; 30-day perinatal survival of at-least-one twin was 84.2% (16/19). In a multivariate logistic regression model, 2 characteristics were associated with the development of TTTS: (1) gestational age <20 weeks at the time of diagnosis of iPoly (odds ratio, 13.48; 95% confidence interval, 3.40-53.48; P = .0002); and (2) intrauterine growth restriction of the co-twin (odds ratio, 7.28; 95% confidence interval, 1.72-30.88; P = .0071).

CONCLUSION

Among referred patients with midtrimester iPoly, 29.7% subsequently developed TTTS. Early diagnosis (<20 weeks) and/or co-twin intrauterine growth restriction were significant risk factors for development of TTTS in these patients.

[Research of placental vascular distribution and clinical outcome in monochorionic twins]

OBJECTIVE

To study the placental vascular distribution of monochorionic (MC) twins with twin-to-twin transfusion syndrome (TTTS) or birth weight discordance.

METHODS

Twenty-eight MC placentas were injected in Peking University Third Hospital between Feb. 2010 and Feb. 2011. The vascular distribution type (parallel, crossed, mixed and monoamniotic), the anastomosis of vessels and the placental sharing were recorded. The outcome of pregnancy and the placental characteristics of birth weight discordance (birth weight discordance≥20%) in non-TTTS MC twins were analyzed.

RESULTS

(1) The outcome of pregnancy: the miscarriage or gestational weeks of 28 MC twins were 20 to 38 weeks (median of 35 weeks). Six cases were TTTS, 3 of which received fetoscopic laser occlusion of communicating vessels (FLOC). There were 48 live births, with an average birth weight of (2036±623) g. (2) Type of placental vascular distribution:in the 28 MC placentas, number of parallel, crossed, mixed and monoamniotic type of placental vascular distribution were 4 (14%), 14 (50%), 6 (21%) and 4 (14%) cases, respectively. No parallel type was found in TTTS. There was no significant difference of vascular anastomosis or unequal placental sharing among the different placental vascular distribution types (P>0.05). (3) Characteristics of placental vascular distribution in birth weight discordance twins:there were 20 non-TTTS MC twin pregnancies, all of which got live births of both babies. Birth weight discordance equal to or more than 20% was found in 6 pairs of newborns, while birth weight discordance less than 20% was found in the rest 14 cases. Ratio of unequal placental sharing was significantly different between the two groups (P<0.01). There was no significant difference of umbilical cord insertion, placental vascular distribution and anastomosis in the two groups (P>0.01).

CONCLUSIONS

Vascular distribution type of MC twins might be related to TTTS. Unequal placental sharing is a risk factor of birth weight discordance in non-TTTS MC twins.

The vascular anastomoses in monochorionic twin pregnancies and their clinical consequences

Monochorionic twin pregnancies are at increased risk of adverse outcome because of the vascular anastomoses that connect the 2 fetal circulation systems. The shared circulation is responsible for some unique complications in monochorionic twins, such as the twin-to-twin transfusion syndrome, the twin anemia polycythemia sequence, the twin reversed arterial perfusion sequence, and monoamniotic twinning. Another consequence of the shared circulation is that the well-being of one twin critically depends on that of the other. In this review, we will describe the technique of placental injection. Further, we will discuss the role of the vascular anastomoses in each of the complications described above and provide an update on their management.

First-trimester ultrasound examination and the outcome of monochorionic twin pregnancies

OBJECTIVE

To refine the incidence of abnormal first-trimester ultrasound measurements and their correlation with the outcome of monochorionic diamniotic pregnancies.

METHODS

First-trimester crown-rump length (CRL) and nuchal translucency thickness (NT) measurements were studied in three subgroups of a total of 200 monochorionic twin gestations referred to our center between June 2002 and February 2006. Intertwin CRL discordance was defined as > 10% and the 95th percentile of NT thickness for gestational age was used. The first group of 103 consecutive unselected monochorionic diamniotic twin pregnancies was prospectively followed up from 11-14 weeks onwards, throughout the pregnancy. The second group of 136 nonconsecutive monochorionic diamniotic twin pregnancies including 64 that developed TTTS was studied retrospectively. The third group of 100 consecutive cases of TTTS studied retrospectively for the correlation between first trimester measurements and staging and timing of occurrence of TTTS.

RESULTS

In group 1, the incidence of TTTS was 5 in 103 (5%, 95CI [0.7-9]). Large intertwin CRL discordance and increased NT were correlated with perinatal death. In group 2, no significant association was found between first-trimester parameters and the development of TTTS but discordance in early second trimester biometry and Doppler were. In group three, a positive correlation was found between the intertwin discordance in CRL and early occurrence of TTTS before 20 weeks of gestation (p = 0.02).

CONCLUSION

Monochorionic twin gestations who ultimately develop TTTS may exhibit intertwin difference in growth as early as 11-14 weeks of gestation. The earlier the discordance the earlier the development of the disease.

Acute twin-twin transfusion syndrome: a case report

BACKGROUND

Clinically relevant acute twin-twin transfusion syndrome (TTTS) is a rare and poorly defined placental pathology because the definitions of chronic TTTS do not apply. Antepartum cases of acute TTTS are infrequently described in the literature despite the presence of vascular anastomoses in most monochorionic placentas.

CASE

A case of otherwise-unexplained acute fetal distress in a monochorionic twin gestation led to an emnergeincy cesarean section and was found to be due to acute heiodynamiic inbalance secondary to activation of a large placental venovenous anastomosis.

CONCLUSION

Obstetricians should be aware of this potential cause of sudden fetal distress in monochorionic twin gestations.

Velamentous cord insertion and unequal placental territories in monochorionic twins with and without twin-to-twin-transfusion syndrome

OBJECTIVE

The objective of this study was to determine the incidence of velamentous cord insertion and placental territory discordancy in monochorionic twins with and without twin-to-twin transfusion syndrome (TTTS).

STUDY DESIGN

All consecutive placentas of monochorionic twins delivered at our center between June 2002 and April 2006 were studied with vascular injection of the umbilical vessels with colored dyes. Velamentous cord insertions were recorded and individual placental territories were calculated by computer analysis.

RESULTS

A total of 76 monochorionic placentas with TTTS and 63 monochorionic placentas without TTTS were studied. The incidence of velamentous cord insertion (per fetus) in the TTTS group and the non-TTTS group was 13% (20 of 152) and 14% (18 of 126), respectively (P = .79). Placental territory discordancy in the TTTS group and the non-TTTS group was 20% and 20% (P = 0.83). In the TTTS group, donor twins had a velamentous cord insertion more often than recipient twins (24% and 3%, respectively, P < .001) and a smaller placental territory (44% and 56%, respectively, P < .001).

CONCLUSION

Our findings suggest that velamentous cord insertion and unequal placental territory are not critical factors for the development of TTTS.

[Specific aspects of monochorionic pregnancies]

Monochorionic pregnancies are at high risk of developing foetal and neonatal complications due to the presence of placental vascular anastomoses. These vascular anastomoses circulate on the chorionic plate and connect directly or indirectly the two foetal circulations. They may cause acute and chronic hemodynamic imbalance between the two foetuses and may cause significant morbidity, especially in the survivor at the time or nearly after the intrauterine death of its co-twin. In addition, some monochorionic pregnancies are complicated by twin-to-twin transfusion syndrome or twin-reversed-arterial-perfusion sequence. The late embryo division (>8 days following the fertilization) originates in monoamniotic monochorionic pregnancy and conjoined twins and is also at risk of developing specific complications related to these conditions. Ultrasound represents the angular stone in the management of these pregnancies, firstly for the diagnosis of monochorionicity in the first trimester, and second by screening and monitoring of their specific complications.

Feto-feto-fetal transfusion syndrome in monozygotic monochorionic triamniotic triplets: vascular evaluation by a cast model

A unique cast model of the placenta in a rare case of feto-feto-fetal triplet transfusion syndrome (FFFTTS) allowed the demonstration of why the transfusion syndrome developed in one fetus and not in the other two in that single placenta. The vasculature anatomy of a monochorionic triamniotic triplet placenta with FFFTTS of three healthy infants (one donor, two recipients) born in the 35th week of gestation was cast by means of dental casting materials. After the cast hardened, the tissue was corroded, revealing the cast blood vessels. The diameters and lengths of the chorionic blood and intraplacental vessels of the cast placenta were measured with a digital caliper. The cast revealed two artery-artery (A-A) anastomoses on the chorionic plate between the two recipients and the donor. Seven artery-vein (A-V) deep anastomoses connected only the arteries of the donor and the veins of the two recipients. The blood vessel connections among the fetuses allowed the evaluation of a pathologic case with its own control in a single placenta. From the vascular appearance, we speculate that the A-A anastomoses between the two fetuses protected them from developing blood transfusions, but that the A-V anastomoses contributed to their development.

Twins and more--1. Some current thinking on multiple births

The incidence of multiple births is rising in many countries including the U.K., mainly as a result of treatment for infertility. Parents of twins, triplets or more require specific information, advice and support at all stages of parenting from diagnosis of a multiple pregnancy onwards. Specialist midwives have an important role to play in this, as do voluntary organisations such as the Multiple Births Foundation. The first part of this two-part article provides an update of some current thinking on multiple births, including twin-twin transfusion syndrome. Part two will provide information about the needs of families with a multiple birth in the early years.

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.

The progression of disease stage in twin-twin transfusion syndrome

OBJECTIVE

To estimate the frequency of progression or regression of disease stage in pregnancies complicated by twin-twin transfusion syndrome (TTTS) managed with non-placental laser techniques.

METHODS

A cohort of TTTS pregnancies within the sole perinatal center for the state of Western Australia was examined. All cases of prenatally identified TTTS from 1992 to 2002 were staged at diagnosis (retrospectively prior to 2000, prospectively since). Amnioreduction and septostomy were the principal therapies used. Features associated with progression, regression or stability were identified.

RESULTS

During the study period, 71 cases of TTTS were managed. Amnioreduction was performed in 73.2%, with no difference in the median number of procedures by stage (p = 0.178). In 21.1% of cases, TTTS resolved completely with persistent normalization of amniotic fluid volumes after amnioreduction (median number of procedures: 2). Disease resolution was associated with pregnancy prolongation, greater gestational age at delivery (36 weeks vs. 28.4 weeks, p < 0.001) and increased perinatal survival (100% vs. 42.6%, p < 0.001) compared with stage progression. Logistic regression analysis predicted that the probability of both infants surviving was 80% if the pregnancy remained at Stage I or II throughout, compared with a probability of 50% if it reached Stage III or more at 26 weeks, and only 25% if the disease reached Stage III or more at 16 weeks' gestation.

CONCLUSION

Pregnancy outcome for TTTS managed with amnioreduction techniques is correlated with stage at diagnosis and the subsequent disease evolution. However, the progression of stage in TTTS is unpredictable and the likelihood of spontaneous fetal demise was not different between stages.

Reversal of twin–twin transfusion syndrome: frequency, vascular anatomy, associated anomalies and outcome

OBJECTIVE

To determine the frequency of reversal of transfusional gradient and phenotype in a large cohort of prospectively studied cases of twin-twin transfusion syndrome (TTTS) and seek evidence of clinical or placental anastomotic associations.

METHODS

Consecutive cases of TTTS seen over an eight-year period with serial documentation of ultrasonic growth, liquor volume and fetal and placental Doppler studies were reviewed. Postnatal injection studies were inspected.

RESULTS

Reversal of TTTS occurred in 5 of 96 affected pregnancies (5%). Two of the five cases had underlying aneuploidy or genetic syndrome, higher than the 2% frequency found in cases without reversal of TTTS (p < 0.05). Placental anastomotic configurations provided no consistent explanation for reversal of phenotype.

CONCLUSION

This study documents the frequency of reversal of the direction of TTTS, and suggests that it is a heterogeneous condition. Reversal of donor-recipient phenotype may be explained by haemodynamic changes secondary to underlying aneuploidy/genetic syndromes, to the presence of multiple anastomoses in either direction or following laser ablation. This series together with previous case reports argues for a high level of suspicion for underlying aneuploidy, genetic syndrome or structural defects where there is reversal of the donor-recipient phenotype.

Twin-twin transfusion syndrome

The understanding and management of twin-twin transfusion syndrome has evolved significantly over the past few years. Improved and standardized sonographic diagnostic criteria, understanding of the heterogeneic nature of the syndrome, development of an anatomical and reproducible surgical technique for the identification of vascular anastomoses, and technological advances and developments now allow clinicians to view the disease as a more readily understandable and treatable condition. Many tasks remain, including education of peers, better screening and diagnosis, and further development of surgical instruments. Generalization of treatment outcomes should no longer apply given the varied results with disease stage. Confirmation of our tailored approach to management of the disease according to stage should soon be corroborated with an appropriate clinical trial.

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.

Transmitted arterio-arterial anastomosis waveforms causing cyclically intermittent absent/reversed end-diastolic umbilical artery flow in monochorionic twins

OBJECTIVES

To characterize the phenomenon of retrograde transmission of arterio-arterial anastomosis (AAA) interference patterns on umbilical artery (UA) waveform by (a) documenting the periodicity, (b) correlation with in vivo and in vitro demonstration of AAAs and (c) reproducing these patterns by computer modelling.

METHODS

Monochorionic twins (MC) twins underwent placental and umbilical Doppler studies. AAAs were sought by pulse wave Doppler of their bi-directional interference pattern and confirmed by postnatal injection studies. The periodicity of transmitted patterns in the UA was determined. Determinants of the transmitted patterns were ascertained by computer modelling of physiological and fetal variables.

RESULTS

Among 83 prospectively studied MC twin pregnancies; a transmitted pattern was observed in 6 (7 per cent) patients for 15-114 days. This was found in 20 per cent (6/30) of smaller MC twins discordant for growth restriction but in no appropriately grown twins. It was only observed in association with AAAs validated both in vivo and in ex vivo. Computer modelling demonstrated that this pattern could be reproduced by summating end diastolic flow with a high pulsatility index in the UA in the presence of a large AAA. Consistent with this, MC twins with a transmitted pattern had larger AAAs (median diameter 4.3 mm interquartile range 4.1-5.2) compared to MC twins discordant for intrauterine growth restriction (2.1 mm interquartile range 1.5 to 2.8) (P<0.05) without a transmitted pattern. Perinatal mortality was similar in the fetuses with and without transmitted patterns (0/12 vs. 2/48 P=0.7).

Rapid onset of severe twin-twin transfusion syndrome caused by placental venous thrombosis

We report a case of rapid onset of severe twin-twin transfusion syndrome (TTTS) at 25 weeks gestation in a monochorionic twin pregnancy that was uneventful before that time. Thrombosis of a main venous branch draining several arteriovenous (AV) anastomoses to the donor changed the previous hemodynamic balance that existed between multiple bidirectional AV anastomoses. The opposing AVs became hemodynamically uncompensated and, despite amnioreductions, severe TTTS developed. At 27 weeks a cesarean section was performed because of worsening cardiotocography parameters of both fetuses. Birth weights were 750 and 1840 g, and initial hemoglobin concentrations were 9.2 and 13.4 mmol/liter for donor and recipient, respectively. The recipient twin died 5 months later of an ischemic, necrotic, and perforated small intestine due to a thrombosed superior mesenteric artery. The donor is well at 2.5 years. No abnormalities in several factors associated with thrombophilia, including factor V Leiden mutations, were found in the parents.

Demonstration of placental vascular anatomy in monochorionic twin gestations

Invasive treatment modalities for severe chronic twin-to-twin transfusion syndrome (TTTS), such as fetoscopic laser coagulation of communicating vessels, have revived the need for detailed studies of placental angioarchitecture. We describe a practical placental vascular injection technique using alcohol-resistant tissue-staining dyes. Injection of color-coded gelatin-dye mixtures effectively delineated the intertwin vasculature, and allowed unequivocal macroscopic classification of vascular communications as artery-to-artery, vein-to-vein, or deep artery-to-vein anastomoses. The existence of deep artery-to-vein anastomoses was further confirmed by light microscopic demonstration of venous dye of one twin and arterial dye of the opposite twin within the same stem villus. Furthermore, the injection technique allowed determination of the caliber of the anastomoses, the direction of the artery-to-vein anastomoses, and the relative vascular territory of each twin. Documenting the vascular communications in monochorionic twin placentas with and without TTTS may enhance our understanding of the pathogenesis of chronic TTTS. Correlating the anastomotic patterns and location of the laser coagulation scars with post-ablation outcome will aid in the design of rational therapeutic methods for this often lethal condition.

Pathogenesis of twin-twin transfusion syndrome: the renin-angiotensin system hypothesis

In spite of active perinatal management, twin-twin transfusion syndrome (TTTS) remains a severe disease with a high risk of neonatal mortality and morbidity. TTTS initially results from an unbalanced blood flow from a donor to a recipient twin. However, its pathogenesis remains unclear, although cardiovascular disturbances and regulation of fetal volemia and diuresis seem central in this syndrome. Previously, we demonstrated that the renin-angiotensin system (RAS) was up-regulated in donor twins as a consequence of hypovolemia, and down-regulated in recipients. This was the first evidence of the implication of the RAS in TTTS. We hypothesize that the RAS plays a key role in the pathogenesis of TTTS. In the donor, RAS up-regulation aggravates oligohydramnios and may increase arterial resistance, which could contribute to placental dysfunction leading to intrauterine growth restriction. In the recipient, paradoxical RAS activation, due to transfer of effectors such as angiotensin II through placental shunts, could explain fetal vascular disturbances and cardiomyopathy. According to our hypothesis, TTTS would appear similar to the classical model of hypertension referred to as '2 kidneys-1 clip' with a donor twin, comparable to the clipped kidney, intoxicating its cotwin, comparable to the normal kidney.

Twin-to-Twin Transfusion Syndrome Results From Dynamic Asymmetrical Reduction in Placental Anastomoses: A Hypothesis

Although placental vascular anastomoses between the fetoplacental circulations are ubiquitous in monochorionic twin pregnancies, the factors regulating their formation and maintenance are not understood. Increasing evidence implicates asymmetric anastomotic patterns in the aetiology of severe twin-to-twin transfusion syndrome (TTTS). The authors propose that anastomoses between placental circulations in monochorionic twins occur in a random manner at the embryological stage of connection of embryonic and extra-embryonic circulations. Placental expansion is then associated with random disruption of anastomoses and regression of their associated villus districts. TTTS develops as discordant loss of anastomoses results in asymmetrical flow resistance. Pregnancies with fetal growth concordance but discordant nuchal translucency at 10-14 weeks are at increased risk of developing subsequent severe TTTS because these clinical features indicate significant pressure differentials in the presence of a placentoplacental circulation, consistent with the presence of numerous, asymmetric anastomoses. However, since the anastomotic pattern is dynamic in the first half of pregnancy this hypothesis predicts that it will not be possible to devise a clinical test at 12 weeks that will predict with certainty the outcome of monochorionic twin pregnancies in relation to TTTS because this depends on random subsequent events.

Twin-twin transfusion syndrome: etiology, severity and rational management

The twin-twin transfusion syndrome is a serious complication of monochorionic twin pregnancies. Partly as a result of an inadequate understanding of the pathophysiology of the syndrome, there is a lack of consensus in clinical management. We sought to review the available information on the etiology of twin-twin transfusion syndrome, to identify parameters that contribute to the severity of the syndrome, and propose a rational management plan based on pathophysiology, clinical presentation and the efficacy of therapies. We therefore amalgamated recent advances in twin-twin transfusion syndrome computer modelling and clinical studies, particularly on therapeutic outcomes. We found that the oligo-polyhydramnios sequence that defines twin-twin transfusion syndrome prenatally represents a wide continuum of severity in the imbalance between the fetoplacental circulations of both twins. In severe twin-twin transfusion syndrome cases, in which the circulatory imbalance deteriorates beyond fetal control, fetoscopic laser therapy of all anastomoses along the placental vascular equator is predicted to have significantly better survival rates and fewer neurological sequelae than amnioreduction. In contrast, mild twin-twin transfusion syndrome cases have better outcomes after one or at most a few amnioreductions than laser therapy, as a result of significantly fewer procedure-related risks. In conclusion, optimal individual therapy may possibly achieve an 85% survival rate in twin-twin transfusion syndrome, but requires advancement in non-invasive criteria that predict the severity of the syndrome. Identifying such criteria is a future challenge. For the interim, twin-twin transfusion syndrome diagnosed before 26 weeks' gestation has significantly better survival rates and fewer neurological sequelae after laser therapy than amnioreduction. Twin-twin transfusion syndrome diagnosed after 26 weeks can best be treated by amnioreduction, or delivery. Contrary to previous claims, fetoscopic laser therapy has outgrown its experimental status. Although improvements in technique and technology are likely, laser placental ablation has a firm scientific and clinical basis.

Renal tubular dysgenesis-like lesions and hypocalvaria. Report of two cases involving indomethacin

We describe a case of twins with twin-to-twin transfusion syndrome (TTS) who were found to have renal tubular dysgenesis (TRD)-like lesions and hypocalvaria attributed to indomethacin treatment of the mother for acute polyhydramnios. History of pregnancy, postnatal clinical course, pathological findings of the kidneys, and the skulls are presented and discussed. These findings include incompletely differentiated proximal tubules in the kidneys and hypoplastic calvaria in both twins. The renal tubular lesions were more marked in the donor than in the transfused twin, probably due to the greater degree of ischemia in that twin. This seems to be in favor of a vascular etiology of the renal defects. However, the fact that similar renal lesions and hypocalvaria were also present in the transfused twin seems to indicate that indomethacin played a role in their onset. This so-called kidney-skull connection has never been reported in conjunction with indomethacin therapy.

Doppler detection of arterio-arterial anastomoses in monochorionic twins: feasibility and clinical application

The accuracy of in-vivo detection of arterio-arterial anastomoses (AAA) in monochorionic (MC) twins and its predictive value for twin-twin transfusion syndrome (TTTS) was assessed in 105 consecutive MC twins scanned at fortnightly intervals. AAA were sought using spectral and colour energy Doppler and ultrasound findings were compared with placental injection studies. AAA were identified in vivo in 59 (56%) pregnancies and at injection study in 68 (65%). The overall sensitivity and specificity was 85 and 97.3% respectively for the detection of AAA. Detection rates were higher at later gestations, with anterior placentae and with larger diameter AAA. The median insonation time to detect an AAA was 10 min (range 1-30). Where an AAA was identified, 15% of pregnancies (nine of 59) developed TTTS compared to 61% (28 of 46) when no AAA was seen (odds ratio 8.6). We conclude that AAA can be detected in vivo with high sensitivity and specificity without undue prolongation of scanning times and have a role in risk stratification in the antenatal assessment of MC twins.

Anticipating twin-twin transfusion syndrome in monochorionic twin pregnancy. Is there a role for nuchal translucency and ductus venosus blood flow evaluation at 11-14 weeks?

Twin-twin transfusion syndrome is a major complication of monochorionic twin pregnancies. In foetuses from monochorionic twinning the presence of increased nuchal translucency thickness (NT) has been associated with an increased risk of developing this syndrome. One of the presumed mechanisms of increased NT is early cardiac failure, indirectly indicated by abnormal blood flow in the ductus venosus. We present eleven cases of monochorionic twin pregnancies in which nuchal translucency thickness and ductus venosus blood flow evaluation was performed at 11-14 weeks. In the two cases presenting with nuchal translucency discrepancy between the two foetuses along with anomalous ductus venosus blood flow in the foetus with increased nuchal translucency, twin-twin transfusion syndrome (TTTS) eventually developed. In none of the twins displaying no inter-twin difference in NT measurements and in those with discrepant NT but normal flow in both ductus venosus, was the progression to TTTS observed. In the two cases which developed TTTS, foetoscopic laser coagulation of the vascular anastomosis was successfully carried out at 18 weeks and normalisation of the venous return was registered. These findings suggest that the association of increased NT and abnormal flow in the ductus venosus in monochorionic twins may be an early manifestation of haemodynamic imbalance between the donor and the recipient eventually manifested as twin-twin transfusion syndrome. Further studies, however, are necessary to establish the potential role of the combination of NT and ductus venosus blood flow assessment as a screening method for TTTS.

[Monochorionic twin pregnancies : dangerous liasons]

Monochorionic twin pregnancies are characterized by a shared placental circulation; this induces a high degree of hemodynamic interdependency between the twins. This is particularly dramatic in twin-to-twin transfusion syndrome or when one twin dies in utero. In both conditions, the severity of the hemodynamic imbalance can lead to significant sequelae in 15-25% of the cases. Ischemic accidents can be prevented by interruption of placental anastomoses through laser coagulation of their chorionic branches. This can be performed when intrauterine death of one twin is inevitable or as a first line treatment in severe TTS. In the latter indication it is important to compare this approach with serial amniodrainage.

[Twin to twin transfusion syndrome]

The incidence of multiple pregnancy has increased by 1.7 times from 1980-1994. Twenty-five percent of all twins are monochorionic diamnionic. The perinatal mortality of monochorionic twins is five times greater than that found in dichorionic twins and the morbidity is eight times greater. The increase in morbidity is due to prematurity, cerebral lesions and congenital malformations. One of the reasons for the increased morbidity is twin-twin transfusion syndrome (TTTS). TTTS occurs in 10-30% of monochorionic twins. TTTS can be treated by either amniocenteses or by lasercoagulation of anastomoses in the placenta. This paper describes the syndrome and reviews the literature. A multination randomized study is necessary to decide which treatment should be preferred.

Effects of placental chorionicity on outcome in twin pregnancies. A cohort study

OBJECTIVE

To examine the effects of the chorionicity of the placenta on infant outcome at 1 year of age in twin pregnancies.

STUDY DESIGN

Cohort study and retrospective review of the medical records of 44 monochorionic (MC) and 164 dichorionic (DC) twin gestations that had been followed at our institution since < 20 weeks' gestation. Physical and neurologic status was assessed at 1 year of corrected age in infants born to these 208 women.

RESULTS

Adverse infant outcomes, such as death, cerebral palsy and mental retardation, occurred in 9 (10%) of 88 MC infants (4 deaths and 5 disabled infants) as compared with 12 (3.7%) of 328 DC infants (6 deaths and 6 disabled infants) (P < .05). Although delivery occurred one week earlier in MC than in DC twins (34.7 +/- 2.8 vs. 35.7 +/- 2.3 weeks, P < .01), there was no significant difference in gestational age at birth or birth weight between the 9 MC and 12 DC infants with adverse outcomes. A presumptive antenatal diagnosis of twin-twin transfusion syndrome (TTTS) was made in 14 (32%) of the 44 MC twin gestations. TTTS was considered to be responsible for adverse outcome in 7 MC infants. All 9 MC infants with adverse outcomes and 4 (33%) of 12 DC infants with adverse outcomes belonged to pairs that had weight discordance > or = 25% (P < .01).

CONCLUSION

MC twins had an increased risk of adverse outcomes as compared with DC twins, mainly because of TTTS. In both MC and DC twins, a birth weight discordance > or = 25% was associated with adverse infant outcomes. The number of infants with disabilities at 1 year of age was equal to the number of deaths.

Twin-twin transfusion syndrome

Twin-twin transfusion syndrome is a complication of monochorionic twin pregnancies associated with extremely high perinatal morbidity and mortality. This article describes the ultrasound features associated with this condition and possible pathophysiological mechanisms. Management options are outlined, including recent development such as laser ablation of placental vascular communications.

X-chromosome inactivation patterns do not implicate asymmetric splitting of the inner cell mass in the aetiology of twin-twin transfusion syndrome

The aetiology of twin-twin transfusion syndrome (TTTS) is unclear. We investigated the hypothesis that monochorionic (MC) pregnancies with TTTS are associated with differences in the timing and symmetry of twinning compared to MC twin pregnancies without TTTS. DNA was extracted from the umbilical cord vessels of 26 female MC twins, 14 with and 12 without TTTS on serial antenatal ultrasound. X-inactivation patterns were determined by DNA digestion with Hhal and Hpall followed by polymerase chain reaction for a polymorphic trinucleotide repeat in the androgen receptor gene. Products were quantified by densitometry and results compared to those in peripheral blood samples of adult female controls. The median degree of non-random inactivation was similar in MC twins with TTTS, in MC twins without TTTS, and in adult controls. The percentage of individuals with skewed (> or =30/70%) inactivation patterns was no different in MC twins with TTTS compared to those without TTTS, and was similar to adult controls using either enzyme technique. In conclusion we found no difference in the degree or frequency of non-random X-inactivation patterns in TTTS. X-inactivation patterns do not appear to be a useful tool for studying the symmetry of inner cell mass splitting in monochorionic twins.

Vascular anatomy of monochorionic placenta in relation to discordant growth and amniotic fluid volume

The objective of this study was to determine the chorionic plate vascular anatomy of the monochorionic (MC) placenta in relation to the discordance in fetal growth with or without disparity in amniotic fluid volume. In 58 MC placentae, anastomoses were delineated by dye-contrast injection under optimal physiological conditions. Thirty-two pregnancies were complicated by twin-twin transfusion syndrome (TTTS) (n = 32), of which 16 placentae were from severe disease. Ten pregnancies with fetal growth discordance of >20% and with a normal amniotic fluid index (AFI) were also studied. Sixteen uncomplicated MC pregnancies were used as controls. Severe TTTS placentae (median, m 1; range, r 0 to 2) had significantly fewer anastomoses than those from mild disease (m 2; r 1 to 4; P < 0.01), discordant growth (m 3; r 2 to 6; P < 0.001) and controls (m 5; r 2 to 8; P < 0.001). Placentae from severe TTTS had a single unidirectional deep arteriovenous anastomosis, while milder cases, in addition, had a < or = 1 mm bidirectional superficial arterioarterial (n = 9) or venovenous (n = 6) -type shunts. Multiple arteriovenous anastomoses with a paucity of superficial anastomoses were detected in discordant growth placenta. In contrast, control placentae had multiple shunts which were symmetrical in number, type and size both overall and per placenta. The subchorionic distance in severe TTTS and discordant growth placenta were comparable (m 3.5 cm; r 1.6 to 5.8 cm versus m 3.6 cm; r 2.5 to 5.7 cm), but were greater than the mild disease (m 2.5 cm; r 1.2 to 3.8 cm; P < 0.01) and control groups (m 1 cm; r 0.5 to 2.4 cm; P < 0.001). The perinatal mortality in severe TTTS (57%) was higher than that in the mild TTTS (17%) and growth discordant groups (15%). The paucity of superficial anastomoses with presence of solitary or multiple arteriovenous anastomoses is likely to be associated with severe TTTS and fetal growth discordance of >20% respectively. In contrast, in mild TTTS additional superficial arterioarterial or venovenous channels are present along with single deep arteriovenous anastomoses.

Inter-twin membrane folding in monochorionic pregnancies

This study examines the value of assessing inter-twin membrane folding in monochorionic twin pregnancies in the prediction of twin-to-twin transfusion syndrome. In 83 monochorionic twin pregnancies ultrasound scans were carried out at 10-14, 15-17 and 19-21 weeks to investigate folding of the inter-twin membrane as an early sonographic feature of inter-twin discrepancy in amniotic fluid volume. There were 23 (28%) cases of membrane folding, which was first observed in one case at 10-14 weeks, in 21 cases at 15-17 weeks and in another case at 24 weeks. In 12 (52%) of the 23 cases the pregnancy progressed to severe twin-to-twin transfusion syndrome and 10 of these were treated by endoscopic laser coagulation of the placental vascular anastomoses. In the other 11 cases there was a moderate syndrome with large discrepancies in amniotic fluid volume and fetal size, persisting throughout pregnancy. In the severe group, five pregnancies resulted in live birth of both babies, three in live birth of one and intrauterine death of the other twin and in four cases there were no survivors. In the moderate group, all babies survived and the inter-twin disparity in birth weight was more than 20%. Similarly, all 60 pregnancies with no membrane folding resulted in live births. In all three groups there was an increase in inter-twin disparity in fetal size with gestation and the greatest inter-twin disparities were in those with moderate twin-to-twin transfusion syndrome from as early as the 10-14 week scan. These findings demonstrate that folding of the inter-twin membrane occurs in about one-quarter of monochorionic twins and in about half of these there is subsequent development of severe twin-to-twin transfusion syndrome.

[Single intrauterine fetal death in twin pregnancy]

During a 11 year period (1984-1994) we identified and analysed at the Department of Obstetrics, University Hospital of Zurich, among 541 twin pregnancies 19 with single intrauterine death (SIUD) in the second and third trimester. The preterm delivery rate was 68% and much higher compared to singleton pregnancies at the same institution (17%). The caesarean section rate was 47% and also higher compared to singleton pregnancies (21%) but lower than in a normal twin collective (61%). Two of the surviving twins showed malformations. One of them has in addition of porencephaly, probably due to disruption syndrome. In 12 out of 19 case a monochorionic placenta was found including 5 with twin-twin transfusion syndrome. Surprisingly 8 out of 19 dead fetuses had a velamentous insertion of the umbilical cord. This might suggest a causal relationship to SIUD. 95% showed the same sex. Maternal blood coagulation disorders are rare. From our results we conclude that SIUD is associated with an increased preterm delivery and caesarean section rate. Monochorionic twins and twins with concordant sex demonstrate the highest risk for SIUD. The twin-twin transfusion syndrome is the main single cause for SIUD. The pathophysiologic role of velamentous insertion remains unclear.

The consequences of monochorionic placentation

Monochorionic (MC) placentation occurs in two-thirds of monozygous twins and approximately 0.3% of all spontaneous conceptions. Vascular anastomoses within the placenta allow intertwin transfusion to occur, which is in most cases a normal event. However, imbalance in this flow may lead to the clinical sequelae observed, with acute, chronic or reverse intertwin transfusion. Acute transfusion describes the events following the death of one of an MC twin pair in utero, with an approximately 1 in 4 chance of demise or neurological damage in the co-twin. Chronic intertwin transfusion, otherwise termed feto-fetal transfusion syndrome, arises following the gradual flux of blood from one twin (the donor) to its sibling fetus (the recipient). The ensuing polyhydramnios places the pregnancy at risk of preterm amniorrhexis and/or labour, notwithstanding the specific sequelae seen in these fetuses following chronic in utero insult. Reverse transfusion describes the most bizarre form of intertwin transfusion: acardiac twinning. Retrograde perfusion of one of the twins with deoxygenated blood leads to the formation of a non-viable acardiac parasite and a 'pump twin' struggling to maintain the cardiac output required to perfuse both twins.

The aetiology and management of twin-twin transfusion syndrome

Twin-to-twin transfusion syndrome presents in the mid-trimester with gross discordance in amniotic fluid volume, and complicates 10-15 per cent of monochorionic twins. Recent studies suggest a primary vascular basis in which a paucity of the bidirectional superficial anastomoses normally found in monochorionic twins is unable to compensate for haemodynamic imbalance resulting from unidirectional transfusion along deeper arterio-venous anastomoses. It is associated with high rates of perinatal mortality from ruptured membranes, hydrops and growth restriction, and a significant morbidity from cardiac and neurological sequelae in particular. Serial aggressive amnioreduction is the current treatment of choice, with survival in around two thirds of cases. In the remaining third, with features suggesting a poor outcome, selective fetocide may have a role. Current attempts at vascular ablative therapies have been associated with inferior survival rates, but the long term therapeutic goal remains the identification and ablation of the shared chorionic vasculature.

Twin-twin transfusion syndrome. Three possible pathophysiologic mechanisms

OBJECTIVE

To propose a classification of twin-twin transfusion syndrome based upon three categories of placental anastomotic patterns.

STUDY DESIGN

A mathematical model developed to compute fetal blood volume in monochorionic twins combines fetoplacental circulation with net fetofetal transfusion along placental anastomoses. We included (1) unequal cotyledonic sharing, assuming that smaller fractions cause smaller twins with lower blood pressure, and (2) significantly decreasing anastomotic resistance, combining Poiseuille's law with placental anastomotic growth. Fetoplacental compensatory mechanisms were not studied.

RESULTS

First, unidirectional arteriovenous anastomoses produce steadily increasing fetal discordance by small anastomotic blood flow. Second, arteriovenous plus compensating anastomoses (venoarterial, arterioarterial, venovenous) produce fetal discordance followed by a dynamic steady state of minimal net fetofetal transfusion and large anastomotic flow. This circumstance mitigates further discordant growth. Third, unequal cotyledonic sharing plus superficial compensating anastomoses (arterioarterial, venovenous) produce fetal discordance followed by a steady state of equal fetal growth and small anastomotic flow. The model predictions include spontaneous disappearance and reversal of discordance. Serial measurement of fetal growth patterns and anastomotic flow could identify the syndrome's underlying pathophysiology.

CONCLUSION

Testing the model predictions by relating clinical presentation with placental anatomy could increase our understanding and direct diagnostic and therapeutic strategies to match the underlying placental anatomy.

Umbilical cord coagulation by operative microendoscopy at 16 weeks' gestation in an acardiac twin

Twin reversed arterial perfusion (TRAP) sequence carries high mortality and morbidity in the normal twin due to a hemodynamic imbalance through the feto-fetal vascular anastomosis. This report describes the ultrasound features of TRAP in the first trimester and a new technique for selective fetocide in the early second trimester in monochorionic twin pregnancies complicated by the TRAP sequence. Laser coagulation of the umbilical cord of the acardiac twin was performed under sonoendoscopic control. The blood flow in the umbilical cord of the acardiac twin was successfully arrested and the survivor developed normally. TRAP sequence can be recognized in the first trimester and successfully arrested by microendoscopic surgery.