bluuebunny/crossref_metadata_2025 huggingface dataset:
Response to an Experimental HBV Vaccine Permits Withdrawal of HBIg Prophylaxis in Fulminant and Selected Chronic HBV-Infected Liver Graft Recipients
Authors: Stärkel Peter , Stoffel Michel , Lerut Jan , Horsmans Yves
Published: September 2005

Strategies using lamivudine and hepatitis B immunoglobulins (HBIg) for prevention of hepatitis B virus (HBV) reinfection after liver transplantation (LT) are expensive since life-long treatment is needed. We evaluated the possibility to obtain protective hepatitis B surface antigen (HBsAg) antibody (anti-HBs) titers after LT and to discontinue HBIg prophylaxis after a reinforced course of vaccination against HBV using an experimental adjuvant HBsAg / AS04 vaccine (GlaxoSmithKline Biologicals [GSK], Rixensart, Belgium) in patients transplanted for hepatitis B. Fifteen LT patients on stable low-level immunosuppression were vaccinated with a double dose of the vaccine at 0, 1, 2, 6, and 12 months: 5 patients were transplanted for nonviral diseases and 10 patients were transplanted for HBV on HBIg monotherapy. HBIg were continued during baseline vaccination (0, 1, and 2 months) and when anti-HBs titers determined every 6 weeks dropped below 150 IU/L. Overall follow-up was 18 months. Sustained long-term response to vaccination was defined as anti-HBs titers >500 IU/L without further need for HBIg administration during a follow-up period of at least 12 months. Overall sustained response to vaccination was 53% (8 / 15 patients); 80% (4 / 5 patients) in the nonviral disease group and 40% (4 / 10 patients) in the HBV group (2 /2 fulminant and 2/8 chronically infected patients) developed a sustained long-term response and were completely free of HBIg at the end of the 18-month follow-up. No HBV recurrence, rejection episodes, or side effects occurred during the follow-up. In conclusion, protective anti-HBs titers were obtained in a substantial number of LT patients following a reinforced course of HBV vaccination with vaccines containing new immunostimulating adjuvants. Vaccination seems well tolerated and safe and allows long-term discontinuation of HBIg.
Sequence of Reperfusion Influences Ischemia/Reperfusion Injury and Primary Graft Function Following Porcine Liver Transplantation
Authors: Brockmann Jens G. , August Christian , Wolters Heiner H. , Hömme Ralf , Palmes Daniel , Baba Hideo , Spiegel Hans-U. , Dietl Karl H.
Published: September 2005

The impact of 3 different reperfusion sequences following orthotopic liver transplantation (OLT) in pigs were evaluated. The reperfusion technique commonly performed is primary portal in order to shorten warm ischemic times (WITs). Experimental and clinical data, usually comparing 2 out of 3 possible reperfusion sequences, provide controversial results. OLT was performed in 24 pigs randomized into 3 groups: primary arterial (A), simultaneous (SIM), and primary portal (P) reperfusion. Hemodynamics were continuously monitored and reperfusion injury and primary graft function were assessed by standard serum parameters, histopathological findings, immunohistochemistry for heme oxygenase 1 (HO-1), and heat shock protein 70 (HSP 70). Aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and γ-glutamyl transpeptidase (γGT) following reperfusion were significantly increased for group A when compared to groups SIM and P. Hemodynamics showed significant differences after reperfusion compared to physiological data; differences in group comparisons were not significant. The bile production/100 g liver/hr was significantly higher for group SIM (1.15 mL) compared to group P (0.66 mL) and group A (0.62 mL). Histology and immunohistochemistry significantly correlated with functional results and outcome. Histological score was best for group SIM and worst for group A. HSP 70, being visualized mainly in the hepatocytes, showed higher expression for groups SIM and P. Inversely, HO-1, found in perisinusoidal cells, showed highest expression after primary arterial reperfusion. In conclusion, although associated with a 10-minute longer warm ischemic time, simultaneous reperfusion causes the least reperfusion injury with superior primary transplant function. Primary arterial reperfusion showed the worst overall outcome and highest degree of HO-1 expression.
The Renal-Sparing Efficacy of Basiliximab in Adult Living Donor Liver Transplantation
Authors: Lin Chih-Che , Chuang Feng-Rong , Lee Chih-Hsiung , Wang Chih-Chi , Chen Yaw-Sen , Liu Yueh-Wei , Jawan Bruno , Chen Chao-Long
Published: September 2005

The purpose of this study is to find out whether basiliximab administration will improve postoperative renal function by delaying the start of tacrolimus and decreasing of dosage requirement for tacrolimus in adult living donor liver transplantation (LDLT). Forty-five adult LDLT recipients were enrolled in the study. The induction group (n = 27) was given basiliximab 20 mg on days 0 and 4; tacrolimus administration was delayed until renal function improved. The control group (n = 18) did not receive basiliximab; tacrolimus was given on the first postoperative day. Trough levels of tacrolimus in the induction and control groups were aimed to be maintained at 5 - 10 ng/ml and 10-15 ng/ml during the first week after transplant, respectively. The median follow-up was 22 months (range 10-34 months). The preoperative conditions were poorer in the induction group (Child C, 56% vs. 33%,

P

= 0.01; UNOS 2a, 15% vs. 0%,

P

= 0.02). The intraoperative blood loss was also higher in the induction group than in the control group (median 2,180 ml vs. 495 ml,

P

< 0.01). The median delay in tacrolimus administration in the induction group was 36 hours (range 24-108 hours). Serum creatinine levels at second and third postoperative months were significantly lower in the induction group. The creatinine clearance rate in the induction group was higher at the third month posttransplant (median 72 vs. 57 ml/minute,

P

= 0.04). The incidence of renal insufficiency was significantly lower in the induction group at the third month posttransplant (26% vs. 67%,

P

< 0.01). Blood cholesterol level at the sixth month posttransplant was lower in the induction group (median 152 vs. 196 mg/dl

P

= 0.03). The incidences of acute cellular rejection, bacteremia, and cytomegalovirus (CMV) infection were similar in both groups. In conclusion, for pretransplant critical patients with more intraoperative blood loss, basiliximab induction could prevent early renal dysfunction by delaying the start of tacrolimus and reducing the dose requirement of tacrolimus without increasing graft rejection and infection. Furthermore, it also improved renal function as well as lowered cholesterol levels within 6 months after transplantation.
Tumorigenic study on hepatocytes coexpressing SV40 with Ras
Authors: Sun Beicheng , Chen Meizhen , Hawks Christina , Hornsby Peter J. , Wang Xuehao
Published: September 2005

A model of neoplastic transformation by the combination of SV40 large T antigen (LT), SV40 small T antigen (ST), oncogenic Ras, and human telomerase reverse trasncriptase subunit (hTERT) has become established and replicated in primary human fibroblasts, however, there is no report on human hepatocytes. Here we use cell transplantation model, and show that transplantation of human hepatocytes of HL‐7702 and HL‐7703 expressing Ha‐RasV12 and SV40 LT into subrenal capsule of immunodeficient mice results in fully malignant tumors, in contrast to conventional subcutaneous injections where tumors fail to develop. In GM‐847 cell study, we have found that hTERT is not required for tumorigenic growth in subrenal capsule transplantation, however, it is required in subcutaneous injection assay. These results demonstrate that Human hepatocytes can be transformed under kidney capsule by coexpressing SV40 LT and Ha‐RasV12, neither hTERT nor protein phosphatase 2A (PP2A) inhibition are required for malignant transformation, a gene which increases cell survival in the subcutaneous injection model is not required for tumorigenic growth in subrenal capsule. © 2005 Wiley‐Liss, Inc.
The effect of tamsulosin on the response of the rabbit bladder to partial outlet obstruction
Authors: Levin Robert M. , Longhurst Penelope A. , Whitbeck Catherine , Korstanje Cees
Published: September 2005

Aim

To determine if tamsulosin treatment prevents or decreases the incidence and severity of outlet obstruction‐induced bladder dysfunction in rabbits.

Materials and Methods

Male New Zealand White rabbits were treated with tamsulosin or vehicle for 4 weeks with treatments initiated 1 week prior to sham or obstruction surgery. Cystometry was done on anesthetized rabbits 21 days after surgery. The bladders were then removed, weighed, and prepared for in vitro whole bladder studies. Responses to 32 Hz field stimulation (FS), carbachol, phenylephrine, and KCl were measured.

Results

Obstruction resulted in a significant increase in bladder weight, which was unchanged by tamsulosin treatment and a significant increase in micturition pressure in the vehicle‐treated group but not in the tamsulosin‐treated group. Compliance was significantly decreased in both obstructed groups. The vehicle‐treated obstructed rabbits had a very sharp increase in intravesical pressure as the bladder reached capacity; this was not seen in the tamsulosin‐treated obstructed rabbits. Tamsulosin did not change the pattern of modifications in contractile responses induced by bladder outlet obstruction.

Conclusions

In vitro responses of vehicle and tamsulosin‐treated obstructed rabbit groups in this study were similar. A greater micturition pressure was found for the vehicle‐treated obstructed group than for the tamsulosin‐treated obstructed group, which was probably due to decreased urethral resistance in the latter. On a functional basis, the higher compliance at capacity and decreased micturition pressure in the tamsulosin‐treated obstructed group would be considered beneficial for bladder function. Neurourol. Urodynam. © 2005 Wiley‐Liss, Inc.
Complications following surgical intervention for stress urinary incontinence: A national perspective
Authors: Taub David A. , Hollenbeck Brent K. , Wei John T. , Dunn Rodney L. , McGuire Edward J. , Latini Jerilyn M.
Published: September 2005

Aims

Stress urinary incontinence (SUI) impacts many women. Treatment is primarily surgical. Post‐operative morbidity considerably affects individuals and the health care system. Our objective is to describe complications following surgery for SUI and how they affect resource utilization.

Methods

Utilizing the Nationwide Inpatient Sample (a nationally representative dataset), 147,473 patients who underwent surgery for SUI from 1988 to 2000 were identified by ICD‐9 codes. Comorbid conditions/complications were extracted using ICD‐9 codes, including complication rates, length of stay (LOS), hospital charges, and discharge status.

Results

Overall complication rate was 13.0% (not equal to sum of complication sub‐types, as each woman may have had = 1 complication), with 2.8% bleeding, 1.4% surgical injury, 4.3% urinary/renal, 4.4% infectious, 0.1% wound, 1.1% pulmonary insufficiency, 0.5% myocardial infarction, 0.2% thromboembolic. The “gold standard” surgical technique for SUI, the pubovaginal sling, had the lowest morbidity at 12.5%. Mean LOS increased with morbidity: from 2.9 to 4.1 to 6.1 days for those with 0, 1, and =2 complications respectively (P < 0.001). Similarly, inflation‐adjusted hospital charges increased with morbidity: from $7,918 to $9,828 to $15,181 for those with 0, 1, and =2 complications respectively (P < 0.001). The percentage of patients requiring post‐discharge subacute or home care increased with morbidity: from 4.4% to 8.4% to 14.3% for those with 0, 1, and =2 complications (P < 0.001).

Conclusions

A substantial percentage of women experience complications following surgery for SUI. Post‐operative morbidity leads to dramatically increased resource utilization. Prospective studies are needed to identify pre‐operative risk factors and intraoperative process measures to optimize the quality of care. Neurourol. Urodynam. © 2005 Wiley‐Liss, Inc.
On the numerical modelling of quasi‐static crack growth in linear elastic fracture mechanics
Authors: Heintz P.
Published: September 2005

In this paper we present a strategy for the simulation of a propagating crack under mixed mode linear elastic conditions using a discontinuous finite element method. A key issue is to accurately compute the incremental change in the kink angle of the propagating crack during subsequent steps. We have chosen to work with a domain formulation of the material force vector as a criteria for the propagation direction. We describe the theoretical background together with the numerical implementation in detail and show some results for different loading conditions. Copyright © 2005 John Wiley & Sons, Ltd.
State‐space time integration with energy control and fourth‐order accuracy for linear dynamic systems
Authors: Krenk Steen
Published: September 2005

A fourth‐order accurate time integration algorithm with exact energy conservation for linear structural dynamics is presented. It is derived by integrating the phase‐space representation and evaluating the resulting displacement and velocity integrals via integration by parts, substituting the time derivatives from the original differential equations. The resulting algorithm has an exact energy equation, in which the change of energy is equal to the work of the external forces minus a quadratic form of the damping matrix. This implies unconditional stability of the algorithm, and the relative phase error is of fourth‐order. An optional high‐frequency algorithmic damping is constructed by optimal combination of three different damping matrices, each proportional to either the mass or the stiffness matrix. This leads to a modified form of the undamped algorithm with scalar weights on some of the matrices introducing damping of fourth‐order in the frequency. Thus, the low‐frequency response is virtually undamped, and the algorithm remains third‐order accurate even when algorithmic damping is included. The accuracy of the algorithm is illustrated by an application to pulse propagation in an elastic medium, where the algorithmic damping is used to reduce dispersion due to the spatial discretization, leading to a smooth solution with a clearly defined wave front. Copyright © 2005 John Wiley & Sons, Ltd.
Piecewise uniform bases and energetic approach for discrete constitutive matrices in electromagnetic problems
Authors: Codecasa L. , Trevisan F.
Published: September 2005

In the paper we introduce piecewise uniform edge and face vector functions on a simplicial primal cell complex having geometric structure common to Whitney's vector functions. We also introduce piecewise uniform bases functions in the barycentric dual complex, where the analogous of Whitney's functions does not exist. By using these piecewise uniform bases functions and by exploiting an energetic approach, we construct symmetric positive definite constitutive matrices for discrete Maxwell's equations. We also prove that these constitutive matrices are deeply related to those of the finite elements with Whitney's bases functions. Copyright © 2005 John Wiley & Sons, Ltd.
Efficient cubature formulae for MLPG and related methods
Authors: Pecher Radek
Published: September 2005

The paper introduces four kinds of compact, simple to implement Gaussian cubature formulae for approximating the domain integrals arising in the discrete local weak form (DLWF) of a governing partial differential equation solved by means of the meshless local Petrov–Galerkin method of type MLPG1. The integral weight functions are fixed to be the quartic‐spline weight function of the moving least squares (MLS) method and the function's gradient. The integration domain is a circle in 2D or a sphere in 3D. The fact that the DLWF test functions are directly incorporated into the formulae increases both their exactness degree and their computational efficiency.

A number of numerical tests are carried out in order to asses the accuracy of the cubature formulae. For integrands involving MLS shape functions, the main factor controlling the integration accuracy is found to be the accuracy of the MLS‐approximation. Only a small number of cubature points is thus required to match that accuracy without a need for domain partitioning. The recommended approach for increasing the overall accuracy is by adding more MLS nodes and taking advantage of the computationally inexpensive cubature formulae. Copyright © 2005 John Wiley & Sons, Ltd.
A modified SSOR preconditioner for sparse symmetric indefinite linear systems of equations
Authors: Chen X. , Toh K. C. , Phoon K. K.
Published: September 2005

The standard SSOR preconditioner is ineffective for the iterative solution of the symmetric indefinite linear systems arising from finite element discretization of the Biot's consolidation equations. In this paper, a modified block SSOR preconditioner combined with the Eisenstat‐trick implementation is proposed. For actual implementation, a pointwise variant of this modified block SSOR preconditioner is highly recommended to obtain a compromise between simplicity and effectiveness. Numerical experiments show that the proposed modified SSOR preconditioned symmetric QMR solver can achieve faster convergence than several effective preconditioners published in the recent literature in terms of total runtime. Moreover, the proposed modified SSOR preconditioners can be generalized to non‐symmetric Biot's systems. Copyright © 2005 John Wiley & Sons, Ltd.
Boundary elements with equilibrium satisfaction—a consistent formulation for dynamic problems considering non‐linear effects
Authors: Soares D. , Telles J. C. F. , Mansur W. J.
Published: September 2005

This paper presents a boundary element (BE) formulation with complete dynamic equilibrium satisfaction with respect to the co‐ordinate axis directions and moments, including inertial forces. The new procedure is quite general and very easy to implement into BE existing codes. All the required expressions for both static and dynamic formulations are shown in the text and two dynamic examples, which take into account linear and non‐linear material behaviour, are presented at the end of the paper, showing the potentialities of the proposed methodology. Copyright © 2005 John Wiley & Sons, Ltd.
On 2D elliptic discontinuous Galerkin methods
Authors: Sherwin S. J. , Kirby R. M. , Peiró J. , Taylor R. L. , Zienkiewicz O. C.
Published: September 2005

We discuss the discretization using discontinuous Galerkin (DG) formulation of an elliptic Poisson problem. Two commonly used DG schemes are investigated: the original average flux proposed by Bassi and Rebay (J. Comput. Phys. 1997; 131:267) and the local discontinuous Galerkin (LDG) (SIAM J. Numer. Anal. 1998; 35:2440–2463) scheme. In this paper we expand on previous expositions (Discontinuous Galerkin Methods: Theory, Computation and Applications. Springer: Berlin, 2000; 135–146; SIAM J. Sci. Comput. 2002; 24(2):524–547; Int. J. Numer. Meth. Engng. 2003; 58(2): 1119–1148) by adopting a matrix based notation with a view to highlighting the steps required in a numerical implementation of the DG method. Through consideration of standard C0‐type expansion bases, as opposed to elementally orthogonal expansions, with the matrix formulation we are able to apply static condensation techniques to improve efficiency of the direct solver when high order expansions are adopted. The use of C0‐type expansions also permits the direct enforcement of Dirichlet boundary conditions through a ‘lifting’ approach where the LDG flux does not require further stabilization. In our construction we also adopt a formulation of the continuous DG fluxes that permits a more general interpretation of their numerical implementation. In particular it allows us to determine the conditions under which the LDG method provides a near local stencil. Finally a study of the conditioning and the size of the null space of the matrix systems resulting from the DG discretization of the elliptic problem is undertaken. Copyright © 2005 John Wiley & Sons, Ltd.
Extended Voronoi cell finite element model for multiple cohesive crack propagation in brittle materials
Authors: Li Shanhu , Ghosh Somnath
Published: September 2005

This paper introduces an extended Voronoi cell finite‐element model (X‐VCFEM) for modelling cohesive crack propagation in brittle materials with multiple cracks. The cracks are modelled by a cohesive zone model and their incremental directions and growth lengths are determined in terms of the cohesive energy near the crack tip. Extension to VCFEM is achieved through enhancements in stress functions in the assumed stress hybrid formulation. In addition to polynomial terms, the stress functions include branch functions in conjunction with level set methods, and multi‐resolution wavelet functions in the vicinity of crack tips. The wavelet basis functions are adaptively enriched to accurately capture crack‐tip stress concentrations. Conditions and methods of stability are enforced in X‐VCFEM for improved convergence with propagating cracks. Two classes of problems are solved and compared with existing solutions in the literature for validation of the X‐VCFEM algorithms. The first set corresponds to results for static cracks, while in the latter set, the propagation of cohesive cracks are considered. Comparison of X‐VCFEM simulation results with results in literature for several fracture mechanics problems validates the effectiveness of X‐VCFEM. Copyright © 2005 John Wiley & Sons, Ltd.
On the modelling of complex 3D bulk metal forming processes via the pseudo‐concentrations technique. Application to the simulation of the Mannesmann piercing process
Authors: Berazategui Diego A. , Cavaliere Miguel A. , Montelatici Luca , Dvorkin Eduardo N.
Published: September 2005

The modelling of complex 3D metal forming processes using the flow formulation, implemented via the pseudo‐concentrations technique, requires the development of robust computational strategies for dealing with the velocity and pseudo‐concentration boundary conditions in the zone where the blank–tools contact is developed. A new algorithm, designed to fulfil those requirements, is presented in this paper.

The Mannesmann piercing process is a metal forming operation used in industry for manufacturing metal seamless pipes. The results of the Mannesmann process finite element simulation are particularly dependent on the accuracy and stability of the algorithm used to describe the contact boundary conditions between the forming tools and the blank. The validation of the finite element model is performed by comparing the numerical predictions obtained using the new algorithm with the results of industrial tests. Copyright © 2005 John Wiley & Sons, Ltd.
The probability density evolution method for dynamic response analysis of non‐linear stochastic structures
Authors: Li Jie , Chen Jian‐Bing
Published: September 2005

The probability density evolution method (PDEM) for dynamic responses analysis of non‐linear stochastic structures is proposed. In the method, the dynamic response of non‐linear stochastic structures is firstly expressed in a formal solution, which is a function of the random parameters. In this sense, the dynamic responses are mutually uncoupled. A state equation is then constructed in the augmented state space. Based on the principle of preservation of probability, a one‐dimensional partial differential equation in terms of the joint probability density function is set up. The numerical solving algorithm, where the Newmark‐Beta time‐integration algorithm and the finite difference method with Lax–Wendroff difference scheme are brought together, is studied. In the numerical examples, free vibration of a single‐degree‐of‐freedom non‐linear conservative system and dynamic responses of an 8‐storey shear structure with bilinear hysteretic restoring forces, subjected to harmonic excitation and seismic excitation, respectively, are investigated. The investigations indicate that the probability density functions of dynamic responses of non‐linear stochastic structures are usually irregular and far from the well‐known distribution types. They exhibit obvious evolution characteristics. The comparisons with the analytical solution and Monte Carlo simulation method demonstrate that the proposed PDEM is of fair accuracy and efficiency. Copyright © 2005 John Wiley & Sons, Ltd.
A non‐iterative algorithm based on Richardson's extrapolation. Application to groundwater flow modelling
Authors: Basombrío Fernando G. , Guarracino Luis , Vénere Marcelo J.
Published: September 2005

In this report, a promising third‐order algorithm based on Richardson's extrapolation and Crank–Nicholson's method is studied. The algorithm, having a wide scope for applications, was initially intended to be used for time integration on non‐linear advection–diffusion problems. Then stability, low oscillations and low additional diffusion become important numerical properties. It is shown that this method, using three single steps for extrapolation, is very close to be unconditionally stable. Under the previous requirements it behaves essentially as well as Crank–Nicholson's scheme but with a better performance, at least in relation to spurious oscillations, and perhaps not so good for dispersion properties. In addition the method is third‐order accurate, and provides useful information related to time integration error to be used for time step control. These features indicate that the algorithm is a good candidate to efficiently solve problems with significant variations in time. Additionally, its non‐iterative version saves important amounts of CPU time, specially for applied 3D modelling. To illustrate the good performance of the algorithm we include several tests comparing it with Crank–Nicholson's scheme, and a 2D application to variably saturated groundwater flow modelling. Copyright © 2005 John Wiley & Sons, Ltd.
Robust generation of high‐quality unstructured meshes on realistic biomedical geometry
Authors: Ito Yasushi , Corey Shum P. , Shih Alan M. , Soni Bharat K. , Nakahashi Kazuhiro
Published: September 2005

In this paper, we propose efficient and robust unstructured mesh generation methods based on computed tomography (CT) and magnetic resonance imaging (MRI) data, in order to obtain a patient‐specific geometry for high‐fidelity numerical simulations. Surface extraction from medical images is carried out mainly using open source libraries, including the Insight Segmentation and Registration Toolkit and the Visualization Toolkit, into the form of facet surface representation. To create high‐quality surface meshes, we propose two approaches. One is a direct advancing front method, and the other is a modified decimation method. The former emphasizes the controllability of local mesh density, and the latter enables semi‐automated mesh generation from low‐quality discrete surfaces. An advancing‐front‐based volume meshing method is employed. Our approaches are demonstrated with high‐fidelity tetrahedral meshes around medical geometries extracted from CT/MRI data. Copyright © 2005 John Wiley & Sons, Ltd.
Improvement of the flow formulation by recovery of the hydrostatic pressure using the finite point method
Authors: Dalayeli H. , Hashemolhosseini H. , Farzin M. , Soltani B.
Published: September 2005

Most of the existing numerical methods based on penalty technique, lead to pressure fields, which are not satisfactory especially when crude meshes are used. The present work for the first time, using a simple and effective finite point approach approximates the total hydrostatic stresses. By this new technique, the nodal hydrostatic pressure values are calculated so that the gradient of hydrostatic pressure satisfies the equilibrium equation, with regard to the current distribution of deviatoric stresses. This approach is verified using a cantilever beam with known analytical stress field. It is also applied to a typical 2D axisymmetric bulk metal forming process. The calculated pressure field is then compared with available solutions. The results of the present approach are very encouraging. Copyright © 2005 John Wiley & Sons, Ltd.
Antepartum rupture of the intertwin‐dividing membrane in monochorionic diamniotic twins: a case report and review of the literature
Authors: Nasrallah Fayez K. , Faden Yaser A.
Published: September 2005

We report a case of monochorionic diamniotic twin gestation confirmed by ultrasound visualization of the thin intertwin‐dividing membrane at 32 weeks' gestation. Ultrasound at 36 weeks failed to demonstrate the thin dividing membrane. The pregnancy ended a few days later with spontaneous vaginal delivery of the first twin. The second twin was in transverse lie with no membranes that could be felt around. Severe fetal heart rate deceleration developed, prompting delivery by emergency caesarean section. Cord entanglement was noted at the time of delivery, which resulted in severe perinatal morbidity of the second twin. The antepartum rupture of the dividing membrane must have happened some time between 32 and 36 weeks. The etiology for this intrauterine disruption is unknown.

A review of the literature about the antepartum rupture of the intertwin‐dividing membrane is described, along with its possible causes and complications. In addition, we discuss possible causes of incorrect amnionicity determination, and thus how to minimize these pitfalls. We conclude that antepartum disruption of the intertwin‐dividing membrane is more common than previously thought. Moreover, prenatal ultrasonographic visualization of a dividing membrane in a diamniotic twin pregnancy does not rule out future change in this environment to a monoamniotic one, with all its perinatal morbidity and mortality complications, which result mainly from cord entanglement. This suggests a modification in the method and frequency of the prenatal fetal well‐being follow‐up, as well as the time and mode of delivery. Copyright © 2005 John Wiley & Sons, Ltd.
Haemoglobin differences at birth in monochorionic twins without chronic twin‐to‐twin transfusion syndrome
Authors: Lopriore Enrico , Sueters Marieke , Middeldorp Johanna M. , Vandenbussche Frank P. , Walther Frans J.
Published: September 2005

Objectives

To determine the haemoglobin (Hb) differences at birth in monochorionic (MC) twins without chronic twin‐to‐twin transfusion syndrome (TTTS) in relation to birth order and placental vascular anatomy.

Methods

All consecutive cases of MC twins without chronic TTTS and dichorionic (DC) twins delivered at our centre and admitted to our neonatal nursery between June 2002 and December 2004 were included in our study. We analysed Hb differences at birth and on day 2, in relation to birth order and placental vascular anatomy.

Results

Forty‐five pairs of MC twins and 71 pairs of DC twins were included. Mean Hb differences at birth in MC and DC twins were similar, respectively 1.5 and 1.4 g/dL. Hb differences >5 g/dL at birth were found in 2% (1/45) of MC twins compared to 8% (6/71) in DC twins. On day 2, mean Hb differences in MC twins increased to 3.8 g/dL, and the rate of MC twins with Hb differences >5 g/dL increased to 27% (12/45) (p < 0.001). Mean Hb differences and the percentage of twins with Hb differences >5 g/dL in DC twins did not change on day 2. In MC twins, Hb levels measured on day 2 were significantly higher in second‐born twins than in first‐born twins, respectively 17.7 and 15.5 g/dL (p = 0.002). Hb differences on day 2 were significantly higher in MC twins with superficial vascular anastomoses than those without superficial anastomoses, respectively 4.0 g/dL and 1.5 g/dL (p = 0.036).

Conclusions

Hb differences occur more frequently in MC twins without chronic TTTS than in DC twins, but only when measured on the second day of life. Hb differences in MC twins are associated with birth order and superficial vascular anastomoses. Copyright © 2005 John Wiley & Sons, Ltd.
Current concepts of Down syndrome screening tests in assisted reproduction twin pregnancies: another double trouble
Authors: Maymon Ron , Neeman Ortal , Shulman Adrian , Rosen Hadar , Herman Arie
Published: September 2005

Assisted reproductive technologies (ART) have increased both the number of pregnancies in women beyond the age of 35 and the incidence of multiple pregnancies. Various methods of screening for Down syndrome (DS) were introduced in clinical practice during the last two decades, and specific problems were encountered when they were applied for twin pregnancies. The current review aims to explore the problematic issue of prenatal DS screening in ART twins.

Overall, more women with twin pregnancies (mainly those who conceived via assisted reproduction) are found to be false positive for DS. This is because mid‐trimester maternal serum screening is associated with a higher false‐positive rate secondary to changes in the feto‐placental endocrinologic metabolism, reflected mainly in high human chorionic gonadotrophin (hCG) levels in the ART pregnancies. First‐trimester nuchal translucency (NT) measurement in twin pregnancies is not affected by the problems encountered in serum screening. This sonographic screening approach enables a fetus‐specific identification of those fetuses at high risk of DS and is associated with a lower false‐positive rate than mid‐trimester serum screening.

DS screening in ART twins presents several challenges in determining the most appropriate screening test modality. Whether there is any significant benefit of adding first‐trimester biochemistry or nasal bone scanning in screening ART‐conceived twins awaits further investigation. Copyright © 2005 John Wiley & Sons, Ltd.
Managing twins discordant for fetal anomaly
Authors: Rustico M. A. , Baietti M. G. , Coviello D. , Orlandi E. , Nicolini U.
Published: September 2005

An excess of structural anomalies is observed in twins compared to singletons. Approximately 1–2% of twin pregnancies may face the dilemma of expectant management versus selective termination following diagnosis of an anomaly affecting only one fetus. If the option of selective fetocide is considered, the main variable determining the technique to achieve this aim is chorionicity. In a dichorionic pregnancy, passage of substances from one twin into the circulation of the co‐twin is unlikely due to the lack of placental anastomoses, hence KCl can be injected safely into the circulation of the affected twin to produce fetal asystole. In monochorionic twin pregnancies, selective termination needs to be performed by ensuring complete and permanent occlusion of both the arterial and venous flows in the umbilical cord of the affected twin, in order to avoid acute haemorrhage from the co‐twin into the dying fetus, which may lead to death or organ damage. Bipolar cord coagulation under ultrasound guidance is associated with approximately 70–80% survival rates. Copyright © 2005 John Wiley & Sons, Ltd.
Update on selective reduction
Authors: Evans Mark I. , Ciorica Doina , Britt David W. , Fletcher John C.
Published: September 2005

Over the past 25 years fetal reduction has been utilized to reduce the risks of higher‐order multiple pregnancies that have resulted from overly successful infertility therapies. The demographics of multiple pregnancy patients have evolved over the past decade, with increasing proportions coming from IVF as opposed to ovulation induction, being older and a higher proportion with donor eggs. Genetic diagnosis prior to reduction is becoming more common and is very safe in experienced hands. For all starting numbers, including twins, reduction to a lower number of fetuses reduces fetal losses, prematurity, and infant mortality and morbidity. Copyright © 2005 John Wiley & Sons, Ltd.
Discordant growth in twins
Authors: Kingdom John C. P. , Nevo Ori , Murphy Kellie E.
Published: September 2005

Discordant growth in twins contributes significantly to rates of perinatal morbidity and mortality. These rates vary according to chorionicity, timing of onset and severity. We have reviewed English language literature in Medline since 1980. It is clear that diagnosis of discordant growth has improved due to the use of serial ultrasound examination. Following the detection of differences in fetal size, diagnosis is facilitated by umbilical artery and fetal Doppler studies. Management options vary according to chorionicity, timing of onset and umbilical‐fetal Doppler studies. The mode of delivery in discordant twins remains controversial. We conclude that ultrasound surveillance of twin gestations, combining serial biometry and selective Doppler studies, is effective in the recognition of siginificant intrauterine growth restriction in co‐twins. Differences in etiology and management underscore the imortance of establishing chorionicity routinely as soon as twin gestation is diagnosed. Copyright © 2005 John Wiley & Sons, Ltd.
Invasive diagnostic procedures in twin pregnancies
Authors: Weisz Boaz , Rodeck Charles H.
Published: September 2005

The rising rate of multiple pregnancies and its association with advanced maternal age has expanded the need for prenatal diagnosis in twins and higher order gestations. The complexity of the invasive diagnostic procedures and the risk of loss of an unaffected twin raise significant clinical, technical and ethical issues. In this review we discuss the specific issues of early scanning, counseling and determination of chorionicity prior to invasive procedures in twins. We present the available data describing the risk associated with these procedures in twins and compare data of fetal loss rate from different studies. We also discuss the issues of fetal blood sampling and late karyotyping in twin pregnancies. Copyright © 2005 John Wiley & Sons, Ltd.
Insights into the pathophysiology of twin–twin transfusion syndrome
Authors: Galea Paula , Jain Venu , Fisk Nicholas M.
Published: September 2005

Twin–twin transfusion syndrome (TTTS) is attributed to trans‐anastomotic transfusion between twins. Anastomoses are ubiquitous in monochorionic (MC) placentae, yet TTTS develops in only 15%. Although ex vivo and in vivo studies fail to identify a unique anastomotic signature, TTTS placentae are typically associated with an imbalance in unidirectional arteriovenous anastomoses with absent bidirectional anastomoses. Doppler detection of an artery‐artery anastomosis reduces the chance of TTTS, whereas, in those that develop the disease, it improves stage‐independent survival. Selective laser is often curative, but an increasingly recognized risk of persistent or reverse TTTS may be attributable to atypical arteriovenous anastomoses not identifiable from the chorionic plate. Simple dysvolaemia fails to explain several phenotypic features, including haematological concordancy, recipient hypertension, and reversibly absent end diastolic flow in the donor. The renin‐angiotensin system is upregulated in the donor and downregulated in the recipient's kidneys, while paradoxically raised renin levels in the recipient may contribute to raised afterload along with endothelin. Although research is limited in humans by therapy and the lack of a suitable experimental model, further studies of placental and vascular pathophysiology may not only refine current treatment modalities but may also, in addition, suggest further avenues for downstream management such as genetic predisposition testing or pharmacological intervention. Copyright © 2005 John Wiley & Sons, Ltd.
The sonographic diagnosis of chorionicity
Authors: Shetty A. , Smith A. P. M.
Published: September 2005

The differentiation between mono‐ and dichorionic placentation in twin pregnancies is of clinical importance because of the significant difference in perinatal morbidity and mortality between the two, and the increased surveillance indicated in monochorionic gestations. Application of ultrasonography has enabled very precise prenatal determination of chorionicity. While this is best performed in the first trimester when accuracy approaches 100%, even in the third trimester, using a composite cascade of available sonographic features, accuracy has been reported to approach 97%. While two clearly separate placentae or discordant fetal gender conform to dichorionicity, in most twin pregnancies other features need to be assessed to determine chorionicity. The presence of the ‘lambda’ or the ‘T’ sign in the presence of a single placenta, best determined in the first trimester, is the most reliable indicator of chorionicity, with measurements of the inter‐twin membrane thickness and counting of the membrane layers being less reliable. In this article, we review the sonographic features that help in the accurate depiction of chorionicity. Copyright © 2005 John Wiley & Sons, Ltd.
First‐trimester diagnosis of conjoined twins
Authors: Pajkrt Eva , Jauniaux Eric
Published: September 2005

Conjoined twins are a rare and complex complication of monozygotic twinning, which is associated with high perinatal mortality. Early prenatal diagnosis of conjoined twins allows better counselling of the parents regarding the management options, including continuation of pregnancy with post‐natal surgery, termination of pregnancy or selective fetocide in case of a triplet pregnancy. With the introduction of high‐resolution and transvaginal ultrasound imaging, accurate prenatal diagnosis of conjoined twins is possible early in pregnancy. We have reviewed the medical literature on the early prenatal diagnosis of suspected conjoined twins using a MEDLINE search. Although first‐trimester diagnosis of conjoined twins is feasible, false‐positive cases are common before 10 weeks because, earlier in gestation, fetal movements are limited and monoamniotic twins may appear conjoined. As most parents opt for immediate termination of pregnancy at confirmation of the diagnosis, there are limited data on the prenatal follow‐up of conjoined twins. When the parents opt for conservative management, half of the fetuses die in utero and another 44% will die during the neonatal period. A detailed analysis of case reports where 3D imaging was used indicates that this modality does not improve on the diagnosis made by 2D ultrasound. Overall, very early prenatal diagnosis and first‐trimester 3D imaging provide very little additional practical medical information compared to the 11–14 weeks' ultrasound examination. Copyright © 2005 John Wiley & Sons, Ltd.
Conjoined twins
Authors: Spitz Lewis
Published: September 2005

Conjoined twins have been a source of fascination for both the general public and the medical profession since time immemorial. Their birth was initially viewed as an ominous sign of impending disaster. This was followed by a prolonged period through the Middle Ages and into the nineteenth century when they were regarded as freaks or monstrosities and were exhibited with substantial financial reward at circuses and sideshows. Recently, conjoined twins have attracted intense media interest, which has coincided with increasing success in their separation. This article gives an overview of the role of prenatal ultrasound in assessing the prognosis and discusses the post‐natal surgical management and outcome. Copyright © 2005 John Wiley & Sons, Ltd.
Acardiac anomaly: current issues in prenatal assessment and treatment
Authors: Wong Amy E. , Sepulveda Waldo
Published: September 2005

Acardiac anomaly is a rare condition affecting monochorionic multiple pregnancies. We review this condition with emphasis on its prenatal diagnostic features and treatment options. Due to the parasitic hemodynamic dependence of the acardiac twin on the pump twin, it is important to monitor the pump twin for signs of decompensation and, if indicated, intervene by interrupting vascular supply to the acardiac twin. The goal of treatment is to maximize the pump‐twin's chance of survival. To assist with the decision of when to treat, we suggest a new classification system based on prognostic factors, specifically the size and growth of the acardiac twin and the cardiovascular condition of the pump twin. When the acardiac twin is small and no signs of cardiovascular impairment in the pump twin are present, we suggest serial ultrasound surveillance to detect any worsening of the condition. In cases with a large acardiac twin or rapid growth of the acardiac mass, we recommend prompt intervention. Once treatment is indicated, the intrafetal approach to interrupt the vascular supply to the acardiac twin appears to be superior to cord occlusion techniques as it is simpler, safer and more effective. The first line of treatment, if available, should be ultrasound‐guided laser coagulation or radiofrequency ablation of the intrafetal vessels. Copyright © 2005 John Wiley & Sons, Ltd.
Psychological aspects of prenatal diagnosis and its implications in multiple pregnancies
Authors: Bryan Elizabeth
Published: September 2005

Couples expecting twins are often unrealistically optimistic and are therefore unprepared for the complications as well as the practical and emotional impact the birth of twins can have on the family. All such couples will need information and support throughout the pregnancy and beyond. In this review, the various aspects that should be addressed are discussed, in particular, health care workers and counsellors need to be aware of the stress experienced by parents who have been through prolonged treatment for infertility or who face the special problems associated with the loss of one twin (implies the loss could be other than death). Copyright © 2005 John Wiley & Sons, Ltd.
Management of fetofetal transfusion syndrome
Authors: Robyr R. , Quarello E. , Ville Y.
Published: September 2005

Feto‐fetal transfusion syndrome contributes heavily to high rates of perinatal mortality and morbidity in monochorionic multiple pregnancies. Its prenatal management has been controversial for at least 25 years. We review the recent literature in order to present the basis for a pragmatic reappraisal of the management of this condition. Laser surgery of the chorionic plate inter‐twin anastomoses is the best first‐line treatment when the syndrome develops before 26 weeks' gestation. Survival (including quality of survival) and gestational age at delivery are improved when compared to serial amnioreduction. Second‐line treatment options include repeat‐laser, intra‐uterine blood transfusion, serial amnioreduction, selective feticide using bipolar cord coagulation or elective delivery, depending upon gestational age and the severity of the disease and its complications. We have found that fetoscopic placental surgery has proven itself over simplicity of amnioreduction. There is no evidence that treatment should be customized according to the stage of the disease at diagnosis. Early recognition of the syndrome through fortnightly serial ultrasound follow‐up of all monochorionic pregnancies should ensure timely referral and make up for geographical constraints. Laser surgery should now be available in fetal medicine units that are managing at least 20 cases per year. Copyright © 2005 John Wiley & Sons, Ltd.