Recipient umbilical artery elongation (redundancy) in twin-twin transfusion syndrome

Fetal metabolic adaptations to cardiovascular stress in twin-twin transfusion syndrome

Monochorionic-diamniotic twin pregnancies are susceptible to unique complications arising from a single placenta shared by two fetuses. Twin-twin transfusion syndrome (TTTS) is a constellation of disturbances caused by unequal blood flow within the shared placenta giving rise to a major hemodynamic imbalance between the twins. Here, we applied TTTS as a model to uncover fetal metabolic adaptations to cardiovascular stress. We compared untargeted metabolomic analyses of amniotic fluid samples from severe TTTS cases vs. singleton controls. Amniotic fluid metabolites demonstrated alterations in fatty acid, glucose, and steroid hormone metabolism in TTTS. Among TTTS cases, unsupervised principal component analysis revealed two distinct clusters of disease defined by levels of glucose metabolites, amino acids, urea, and redox status. Our results suggest that the human fetal heart can adapt to hemodynamic stress by modulating its glucose metabolism and identify potential differences in the ability of individual fetuses to respond to cardiovascular stress.

Fortnightly surveillance of monochorionic diamniotic twins for twin to twin transfusion syndrome: Compliance and effectiveness

OBJECTIVES

To determine the compliance and effectiveness of fortnightly ultrasound surveillance for detection of twin-twin transfusion syndrome (TTTS) in monochorionic diamniotic (MCDA) twin gestations.

METHODS

This is a retrospective study of ultrasound surveillance of MCDA twins for TTTS. Our surveillance protocol requires fortnightly ultrasounds starting at 16 weeks of gestational age (GA) continuing until delivery. Compliance was assessed by determining the GA of surveillance initiation and time between ultrasounds. GA and Quintero Stage at diagnosis were evaluated to determine whether TTTS was detected prior to advanced disease (Quintero Stage III +) or fetal demise.

RESULTS

Of 442 women, 264 (59.7%) initiated surveillance after 16 weeks; follow-up ultrasounds were late in 17.4% of cases. TTTS was diagnosed in 43 (9.7%) women at a median GA of 19.7 [17.4, 23.9] weeks. Of 25/43 (58.1%) cases diagnosed during protocol compliance, 12 had advanced disease and two had fetal demise. A similar proportion of diagnoses (n = 18), made while non-compliant, exhibited advanced disease (11/18, 61.1%, P = .40). Thirteen diagnoses occurred during periods of increased ultrasound frequency due to abnormalities (ie, fluid/estimated fetal weight discrepancies or Doppler abnormalities).

CONCLUSIONS

In this population, fortnightly ultrasound compliance was suboptimal. Advanced disease and fetal demise occurred during protocol compliance.

Computational simulations of the helical buckling behavior of blood vessels

Tortuous vessels are often observed in vivo and could hinder or even disrupt blood flow to distal organs. Besides genetic and biological factors, the in vivo mechanical loading seems to play a role in the formation of tortuous vessels, but the mechanism for formation of helical vessel shape remains unclear. Accordingly, the aim of this study was to investigate the biomechanical loads that trigger the occurrence of helical buckling in blood vessels using finite element analysis. Porcine carotid arteries were modeled as thick-walled cylindrical tubes using generalized Fung and Holzapfel-Gasser-Ogden constitutive models. Physiological loadings, including axial tension, lumen pressure, and axial torque, were applied. Simulations of various geometric dimensions, different constitutive models and at various levels of axial stretch ratios, lumen pressures, and twist angles were performed to identify the mechanical factors that determine the helical stability. Our results demonstrated that axial torsion can cause wringing (twist buckling) that leads to kinking or helical coiling and even looping and winding. The specific buckling patterns depend on the combination of lumen pressure, axial torque, axial tension, and the dimensions of the vessels. This study elucidates the mechanism of how blood vessels buckle under various mechanical loads and how complex mechanical loads yield helical buckling.

Discordance of umbilical coiling index between recipients and donors in twin-twin transfusion syndrome

INTRODUCTION

To compare the intertwin umbilical cord coiling in twin-twin transfusion syndrome (TTTS) before fetoscopic laser treatment and to correlate these with Doppler findings in both twins.

METHODS

We performed a prospective study using three-dimensional (3D) ultrasound with color Doppler imaging of the umbilical cord in TTTS. Coiling index was measured as a reciprocal value of one complete vascular coil. Ultrasound hypocoiling was thus defined as < 0.2 coils/cm and hypercoiling as > 0.6 coils/cm, respectively. Umbilical artery pulsatility index (PI) and peak systolic velocity, middle cerebral artery peak systolic velocity and ductus venosus PI of flow-velocity waveformes of both twins were measured.

RESULTS

We included 65 women in the study. The average gestational age was 21.1 ± 2.7 weeks. In 65 recipients and 56 donors coiling index could be quantified. The median (interquartile range) coiling index of recipient twins was significantly higher than of donors, 0.55 (0.41-0.68) vs. 0.26 (0.2-0.5); P < 0.0001. The proportions of abnormal intertwin coiling were significantly (P = 0.0015) different. Out of 65 recipient with coiling indices evaluation, 1 (1.5%) showed hypocoiled and 27 (41.5%) hypercoiled cords. In contrast, 27 donor twins (48.2%) showed hypocoiled and 5 (8.9%) hypercoiled umbilical cords. There were no significant correlations between the fetal Doppler values and coiling indices.

DISCUSSION

Evaluation of umbilical cord coiling index using 3D color Doppler in both twins complicated by TTTS is feasible in both, donors and recipients. Coiling indices differ significantly between recipient and donor twins and do not correlate with Doppler findings.

Bisphosphonate therapy in an infant with generalized arterial calcification with an ABCC6 mutation

Generalized arterial calcification of infancy (GACI) is a rare genetic disorder with high infantile mortality, described to be due to ENPP1, and less commonly ABCC6 mutations. Bisphosphonate treatment has been described to improve survival in ENPP1-positive GACI patients, but few studies have described bisphosphonate treatment in ABCC6-positive patients. Without therapy, patients will die before 6 months of age. Our patient is now 3 years old, former recipient twin of twin-to-twin transfusion syndrome (TTTS). Initial fetal echocardiogram at 19 weeks showed calcifications of the ascending aorta and pulmonary artery (PA). She underwent utero laser therapy, and despite resolution of the TTTS, her follow-up scans showed progressive calcification of the aorta and PA. Postnatal echocardiogram showed calcification and supravalvar stenosis of the aorta and PA. CT on day of life 6 showed calcifications in the PAs, aortic arch, and descending aorta. Quantification of valvular calcification can be difficult; in our patient, increasing outflow tract gradient on echocardiogram was used to monitor disease progression. Molecular testing revealed an ABCC6 gene mutation. She was started on weekly IV pamidronate (0.1-0.3 mg/kg/week) on day 8 of life then transitioned to oral etidronate (15-20 mg/kg/day). Given progressive supravalvar aortic and pulmonary stenosis, she underwent surgical repair with patch augmentation of the PA and ascending aorta at 4 months old. She has done well post-operatively, continuing on enteral bisphosphonate therapy with no side effects to date. Her identical twin was confirmed to have the same mutation and remains asymptomatic with no calcifications. Aggressive bisphosphonate therapy should be started as soon as possible in patients with infantile arterial calcinosis due to ABCC6 or ENPP1 mutations. Echocardiographic evaluation can be used to monitor disease progression by arterial gradients. Molecular testing is also essential to evaluate for possible co-morbidities in these patients and pregnancy management for the future.