Molecular Mechanisms Underlying Twin-to-Twin Transfusion Syndrome.

Twin-to-twin transfusion syndrome is a unique disease and a serious complication occurring in 10-15% of monochorionic multiple pregnancies with various placental complications, including hypoxia, anemia, increased oxidative stress, and ischemia-reperfusion injury. Fetoscopic laser photocoagulation, a minimally invasive surgical procedure, seals the placental vascular anastomoses between twins and dramatically improves the survival rates in twin-to-twin transfusion syndrome. However, fetal demise still occurs, suggesting the presence of causes other than placental vascular anastomoses. Placental insufficiency is considered as the main cause of fetal demise in such cases; however, little is known about its underlying molecular mechanisms. Indeed, the further association of the pathogenic mechanisms involved in twin-to-twin transfusion syndrome placenta with several molecules and pathways, such as vascular endothelial growth factor and the renin-angiotensin system, makes it difficult to understand the underlying pathological conditions. Currently, there are no effective strategies focusing on these mechanisms in clinical practice. Certain types of cell death due to oxidative stress might be occurring in the placenta, and elucidation of the molecular mechanism underlying this cell death can help manage and prevent it. This review reports on the molecular mechanisms underlying the development of twin-to-twin transfusion syndrome for effective management and prevention of fetal demise after fetoscopic laser photocoagulation.

Amniotic fluid microRNA profiles in twin-twin transfusion syndrome with and without severe recipient cardiomyopathy.

BACKGROUND: Twin-twin transfusion syndrome presents many challenges for clinicians, and the optimal means of identifying pregnancies that will benefit most from intervention is controversial. There is currently no clinically available biomarker to detect twin-twin transfusion syndrome or to stratify cases based on the risk factors. microRNAs are small RNAs that regulate gene expression and are biomarkers for various disease processes, including adult and pediatric heart failure. To date, no studies have investigated amniotic fluid microRNAs as biomarkers for disease severity, specifically for severe recipient cardiomyopathy in twin-twin transfusion syndrome cases. OBJECTIVE: This study aimed to assess whether amniotic fluid microRNAs could be useful as biomarkers to identify pregnancies at greatest risk for severe recipient cardiomyopathy associated with twin-twin transfusion syndrome. STUDY DESIGN: Amniotic fluid was collected at the time of amnioreduction or selective fetoscopic laser photocoagulation from monochorionic diamniotic twin pregnancies with twin-twin transfusion syndrome at any stage. Fetal echocardiography was performed on all twins before the procedure, and severe cardiomyopathy was defined as a right ventricular myocardial performance index of the recipient fetus of >4 Z-scores. microRNA was extracted from the amniotic fluid samples and analyzed using an array panel assessing 379 microRNAs (TaqMan Open Array, ThermoFisher). Student t tests were performed to determine significant differences in microRNA expression between pregnancies with severe recipient cardiomyopathy and those with preserved cardiac function. A stringent q value of <.0025 was used to determine differential microRNA expression. Random forest plots identified the top 3 microRNAs that separated the 2 groups, and hierarchical cluster analysis was used to determine if these microRNAs properly segregated the samples according to their clinical groups. RESULTS: A total of 14 amniotic fluid samples from pregnancies with twin-twin transfusion syndrome with severe cardiomyopathy were compared with samples from 12 twin-twin transfusion syndrome control cases with preserved cardiac function. A total of 110 microRNAs were identified in the amniotic fluid samples. Twenty microRNAs were differentially expressed, and the top 3 differentiating microRNAs were hsa-miR-200c-3p, hsa-miR-17-5p, and hsa-miR-539-5p. Hierarchical cluster analysis based on these top 3 microRNAs showed a strong ability to differentiate severe cardiomyopathy cases from controls. The top 3 microRNAs were used to investigate the sensitivity and specificity of these microRNAs to differentiate between the 2 groups with a receiver operating characteristic curve demonstrating sensitivity and specificity of 80.8%. All 20 differentially expressed microRNAs were down-regulated in the group with severe cardiomyopathy. CONCLUSION: Amniotic fluid microRNAs demonstrated differential expression between twin-twin transfusion syndrome recipient fetuses with severe cardiomyopathy and those without and have the potential to be important biomarkers of disease severity in this population.

Twin-twin transfusion syndrome is associated with alterations in the metabolic profile of maternal plasma in early gestation: a pilot study.

OBJECTIVE: Twin-twin transfusion syndrome (TTTS) causes perinatal mortality and morbidity in monochorionic twins. The early recognition of and interventional therapy for TTTS is associated with a more favorable overall prognosis. However, the prediction by the use of ultrasound in the first trimester has relatively poor sensitivity and specificity. This study aimed to identify metabolic biomarkers to aid in ultrasound screening of TTTS. METHODS: Maternal plasma was prospectively collected between 11 and 15 weeks of gestation in apparently uncomplicated monochorionic-diamniotic twin pregnancies. This cohort was divided into: (i) patients who were subsequently diagnosed with TTTS by using ultrasound; (ii) uncomplicated matched controls. Metabolome was profiled by using gas chromatography-mass spectrometry. RESULTS: The levels of fatty acids, organic acids, oxaloacetic acid, and beta-alanine were significantly lower in the TTTS maternal plasma at 11-15 weeks of gestation, and methionine and glycine were also higher (p < 0.05, FDR<0.12). Generally, in TTTS pregnancies, the metabolisms of amino acid, carbohydrate, cofactors, vitamins, and purine were "down-regulated"; whereas bile secretion and pyrimidine metabolism were "upregulated." CONCLUSIONS: The metabolomics scanning of early gestation maternal plasma may identify those pregnancies that subsequently develop TTTS; in particular, downregulated fatty acid levels may be biologically plausible to be implicated in the pathogenesis of TTTS.

Fetal neurodevelopmental recovery in donors after laser surgery for twin-twin transfusion syndrome.

BACKGROUND: Fetal magnetic resonance imaging (MRI) and spectroscopy (MRS) provide a unique opportunity to non-invasively measure markers of neurodevelopment in survivors of twin-twin transfusion syndrome (TTTS). OBJECTIVE: To characterize fetal brain maturation after laser surgery for TTTS by measuring brain volumes and cerebral metabolite concentrations using fetal MRI + MRS. STUDY DESIGN: Prospective study of dual surviving fetuses treated with laser surgery for TTTS. At 4-5 postoperative weeks, fetal MRI was used together with novel image analysis to automatically extract major brain tissue volumes. Fetal MRS was used to measure major metabolite concentrations in the fetal brain. RESULTS: Twenty-one twin pairs were studied. The average (±SD) gestational age at MRI was 25.89 (±2.37) weeks. Total brain volume (TBV) was lower in the donors, although cerebral volumes were not different between twin pairs. Recipients showed lower proportions of cortical and cerebellar volumes, normalized to TBV and cerebral volumes. MRS data showed that biochemical differences between twin brains were related to discrepancy in their brain volumes. CONCLUSION: Although donors have a smaller TBV compared to recipients, proportionality of brain tissue volumes are preserved in donors. MRS maturational markers of fetal brain development show that recovery in donors persists 4 weeks after surgery.

Discordant placental oxygenation and autophagy in twin anemia-polycythemia sequence (TAPS).

BACKGROUND: (Macro)autophagy is an important process of self-degradation of macromolecules and organelles that ensures cellular homeostasis and energy preservation during stressful conditions. Dysregulated placental autophagy has been implicated in a wide range of pregnancy complications. Recent studies identified hypoxia as a key regulator of trophoblast autophagy in vitro; however, its effects on placental autophagy in vivo remain incompletely understood. In this study, we evaluated the monochorionic twin anemia-polycythemia sequence (TAPS) placenta as model of discordant placental oxygenation to determine the effects of hypoxia on placental autophagy in utero. METHODS: We performed a retrospective comparative analysis of tissue oxygenation and autophagy in anemic and polycythemic territories of TAPS placentas (N = 12). Archival tissues were subjected to immunohistochemical, immunofluorescence and Western blot analyses of carbonic anhydrase (CA) IX (hypoxia marker) and key autophagy/lysosomal markers. RESULTS: CAIX protein levels were significantly higher in anemic twin territories than in corresponding polycythemic territories, consistent with relative tissue hypoxia. Anemic placental shares further displayed significantly higher levels of LC3I/II (autophagosome markers) and LAMP1/2 (lysosome markers), associated with upregulated expression of lysosome/autophagosome activity-associated markers, transcription factor EB and cathepsin D. The accumulation of autophagosomes and lysosomes in anemic shares was accompanied by elevated p62 protein expression, suggestive of inhibition of the downstream autophagy pathway. CONCLUSIONS: TAPS placentas display striking intertwin discordance in tissue oxygenation and autophagic activity and may provide a suitable model for study of the interrelationship between hypoxia, autophagy, and pregnancy outcome in a monochorionic twin setting.

Influence of maternal obesity and metabolic and vascular mediators in twin-twin transfusion syndrome.

Obesity is a risk factor for complications in singleton and twin pregnancies; however, there are limited data regarding maternal body mass index (BMI) in the setting of twin-twin transfusion syndrome (TTTS). We hypothesized that increased BMI in TTTS is associated with adverse perinatal outcomes and vascular pathology. A retrospective study of twin reversed arterial perfusion (n = 4), selective intrauterine growth restriction (n = 10) and TTTS (n = 33) was conducted. Treatment included fetoscopic laser photocoagulation (FLP) (n = 35) or Solomon technique (n = 12). Ex vivo placental intravascular injections, immunohistochemistry, and perinatal outcomes were compared by maternal BMI. In pregnancy complicated by TTTS, 16/33 women were obese (BMI > 30 kg/m2) and 11/33 were overweight (BMI 25-29.9 kg/m2). Women who were overweight or obese had an increased rate of premature rupture of membranes (PPROM), cesarean delivery, and/or concomitant co-morbidities when compared to the normal weight group. Duration of neonatal intensive care unit (NICU) admission was longer in neonates of overweight/obese women versus normal weight. Placental examination of FLP sites in the obese group showed larger infarcts, increased adipose triglyceride lipase, and a proangiogenic phenotype. Increased BMI is common in our TTTS cohort and it is associated with higher rate of co-morbidity, PPROM, prolonged NICU stay, and an imbalance of placental metabolic and vascular mediators.

Carbohydrate and fatty acid perturbations in the amniotic fluid of the recipient twin of pregnancies complicated by twin-twin transfusion syndrome in relation to treatment and fetal cardiovascular risk.

INTRODUCTION: Twin-twin transfusion syndrome (TTTS) complicates 15% of monochorionic twin pregnancies, often being associated with recipient cardiac dysfunction. Untreated, it has a fetal mortality rate of at least 90%; although treatment by fetoscopic laser coagulation significantly improves prognosis. Measurement of recipient amniotic fluid metabolites, such as cardiac Troponin T and atrial natriuretic polypeptide, correlate with cardiac function in this fetus. The aim of this study is to describe the amniotic fluid metabolomic profile in TTTS, relate this to fetal recipient cardiac function and assess the metabolomic changes induced by fetoscopic laser coagulation. METHODS: Prospective single centre cohort study. The metabolomics profile of the amniotic fluid from the recipient sac of TTTS pregnancies was assessed using ultra high performance liquid chromatography-mass spectrometry. Profiles were compared pre- and post-laser coagulation and related to fetal recipient cardiac function, as assessed using Doppler ultrasound within 4 h of treatment. RESULTS: Eleven metabolites had significant associations with recipient fetal right and left ventricular myocardial performance index pre-laser. 200 metabolites in recipient amniotic fluid demonstrated a change in relative concentrations when comparing pre- and post-laser coagulation (p < 0.005). The most prominent change is in the balance of carbohydrate and fatty acid metabolic profile contributing to fetal or placental energy metabolism. These changes were also associated with the echocardiographic measures of recipient cardiac function. DISCUSSION: Changes in carbohydrate and fatty acid metabolic profiles are noted in recipients with cardiac dysfunction, and further changes are noted after treatment. Validation and investigation may identify targets for potential pharmacological treatment.

Altered amniotic fluid leptin levels in twin-twin transfusion syndrome with concurrent placental insufficiency.

OBJECTIVE: To measure amniotic fluid leptin levels in fetuses with twin-twin transfusion syndrome (TTTS) with and without placental insufficiency (PI) and determine its usefulness as a biomarker of PI. STUDY DESIGN: A retrospective case control study of TTTS stage III patients from 2009 to 2011 was conducted. Cases were pregnancies with PI (TTTS-PI, n = 18) matched by stage, gestational age, and degree of cardiomyopathy to controls without PI (TTTS, n = 26). PI was strictly defined using biometric parameters. Amniotic fluid from recipient twins (RT) was taken during second trimester fetoscopic laser therapy. Leptin concentrations were determined and compared to growth parameters and birth weight. RESULTS: RT-adjusted leptin was 66% higher in TTTS-PI (p = 0.016) compared to TTTS controls. Cases had significantly higher growth discordance (p = 0.004) and lower RT birth weight (p = 0.041) compared to controls. Significantly higher adjusted leptin levels were observed at birth in the TTTS-PI group when comparing those with SGA donor twins to those of normal weight (p = 0.016). CONCLUSION: These data suggest a role for leptin in pregnancies complicated by TTTS with placental insufficiency. However, further studies are needed to define its mechanism and potential role as a biomarker in amniotic fluid for placental pathophysiology.

Evaluation of prenatal and postnatal diagnostic criteria for twin anemia-polycythemia sequence.

OBJECTIVE: The aim of this study is to analyze the relevance of the prenatal and postnatal diagnostic parameters of twin anemia-polycythemia sequence (TAPS). METHODS: Diagnostic data of all cases of TAPS followed in our institution between 2006 and 2013 were reviewed. Statistical analyses were conducted using Bayesian methods. RESULTS: Twenty cases of TAPS were included. We found a relationship between the hemoglobin level and the middle cerebral artery peak systolic velocity (coefficient -0.25 [-0.34, -0.15], Pr(coef < 0) = 99.99%). Sensitivity and specificity of the prenatal diagnosis were 71% and 50%, respectively, regarding the correspondence with postnatal diagnosis. There was no correlation between the number [odds ratio (OR) = 0.89 [0.72, 1.10], Pr(OR > 1) = 14.8%)], the mean diameter (OR = 0.98 [0.32, 3.06], Pr(OR > 1) = 48.9%), or the total diameter (OR = 0.79 [0.36, 1.53], Pr(OR > 1) = 26.3%) of arteriovenous anastomoses and the severity of TAPS. CONCLUSION: Middle cerebral artery peak systolic velocity is a reliable tool for estimating the hemoglobin level in cases of TAPS. The correspondence between prenatal and postnatal diagnosis is imperfect. Further studies are required to evaluate opportunity of widening postnatal diagnostic criteria. © 2014 John Wiley & Sons, Ltd.

Placental share and hemoglobin level in relation to birth weight in twin anemia-polycythemia sequence.

INTRODUCTION: Twin anemia-polycythemia sequence (TAPS) is a newly described form of chronic twin transfusion. Previous observational studies noted a discordance between birth weight and individual placental share in TAPS. The purpose of this study was to investigate if fetal growth in monochorionic (MC) twins with TAPS is determined by placental share or by the net inter-twin blood transfusion. METHODS: All consecutive MC twin placentas of live-born twin pairs with and without TAPS examined at our center between June 2002 and February 2014 were included in this study. Hemoglobin (Hb) levels and individual placental share were evaluated at birth and correlated with birth weight share. We excluded MC twin pregnancies with twin-twin transfusion syndrome. RESULTS: A total of 270 MC twin pregnancies (TAPS group, n = 20; control group without TAPS, n = 250) were included in this study. Donors with TAPS had a lower birth weight than recipients in 90% (18/20) of cases, but a larger placental share in 65% (13/20) of cases. In the TAPS group, birth weight share was positively correlated with Hb share at birth (P < 0.01) but not with placental share (P = 0.54). In the control group without TAPS, birth weight share was strongly correlated with placental share (P < 0.01) but not with Hb share (P = 0.14). DISCUSSION: A relatively larger placental share may enable the survival of the anemic twin in TAPS. CONCLUSION: In contrast with uncomplicated MC twins, fetal growth in MC twins with TAPS is determined primarily by the net inter-twin blood transfusion instead of placental share.

Maternal plasma and amniotic fluid cytokines in monochorionic, diamniotic twin pregnancies complicated by twin-to-twin transfusion syndrome.

INTRODUCTION: Cytokine imbalance has been implicated in placental-related pathologies, i.e. recurrent miscarriage and pre-eclampsia. Such conditions are more prevalent in multiple pregnancies. Twin-to-twin transfusion syndrome (TTTS) is associated with asymmetric placental blood flow and intra-cardiac pressures. We hypothesised that cytokine expression may be aberrant in this condition and that fetoscopic laser ablation (FLA) may cause local cytokine release. MATERIAL AND METHODS: A prospective cohort of monochorionic, diamniotic twins with TTTS (n = 23) was studied. Circulating T helper cell type 1 (TH1)/TH2 maternal cytokines and cytokine-related and angiogenic factors were measured in plasma and amniotic fluid before and after FLA by human FASTQuant or ELISA. Basal comparisons were made with uncomplicated monochorionic and dichorionic (DC) twins. RESULTS: Median maternal plasma platelet-derived growth factor-BB was highest in uncomplicated DC twins (p = 0.049), whereas tissue inhibitor of metalloproteinases (TIMP)-1 was highest in TTTS twins (p = 0.003). In TTTS amniotic fluid, interleukin (IL)-6, IL-1ß, tumour necrosis factor-α, IL-10, IL-4, IL-8, interferon-γ, TIMP-1 and intercellular adhesion molecule-1 were significantly higher than maternal plasma concentrations. There were no significant differences in plasma or amniotic fluid cytokines after FLA, with the exception of amniotic fluid keratinocyte growth factor, which was significantly reduced. DISCUSSION: TTTS is associated with minimal changes in cytokine levels when compared to uncomplicated twins, although the majority of cytokine levels were higher in amniotic fluid than maternal blood. It does not appear that FLA evokes a significant change in cytokines.

Global gene expression analysis of amniotic fluid cell-free RNA from recipient twins with twin-twin transfusion syndrome.

OBJECTIVE: The objective of this study was to understand the biological pathways involved in twin-twin transfusion syndrome (TTTS) by performing global gene expression analysis of amniotic fluid (AF) cell-free RNA. METHODS: A prospective whole transcriptome microarray study analyzing cell-free RNA in AF from TTTS recipient twins and singleton controls was carried out. Significantly differentially regulated genes in TTTS cases (N = 8) versus matched controls (N = 8) were identified and pathways analyses performed. Significant gene expression differences between stage II TTTS recipients (N = 5) and stage III TTTS recipients with abnormal Doppler measurements (N = 5) were also analyzed. RESULTS: Analysis of paired data from TTTS cases and controls revealed differential expression of 801 genes, which were significantly enriched for neurological disease and cardiovascular system pathways. We also identified cardiovascular genes and pathways associated with the presence of critically abnormal Doppler measurements in stage III TTTS recipients. CONCLUSIONS: This study provides the first transcriptome-wide data on the impact of TTTS on fetal development. Our results show that gene expression involving neurological and cardiovascular pathways are altered in recipient fetuses prior to surgical treatment. This has relevance for the origins of long-term complications seen in survivors and for the development of future fetal biomarkers.

[Expressions of HIF-α and its target gene in monochorionic twin placentas with twin-twin transfusion syndrome].

OBJECTIVE: To determine hypoxia-inducible factor 1α (HIF-1α) and its target gene, vascular endothelial growth factor (VEGF) and receptor (VEGFR-1) concentrations in the placentas of the donor and recipient in monochorionic twin pregnancies with twin-twin transfusion syndrome (TTTS). METHODS: Twenty monochorionic twin pregnancy cases were included in the study (10 with and 10 without TTTS). Tissue protein expressions of HIF-1α,VEGF and VEGFR-1 were determined by using immunohistochemistry. Western blot analysis were used to quantify and compare the protein expression. RT-PCR were used to compare their mRNA expressions. RESULTS: HIF-1α was mainly observed in trophoblastic cells and villi capillaries endothelial cells, and VEGF in trophoblastic cells, endothelial cells and villi stromal cells; VEGFR-1 was mainly observed in villi trophoblastic cells and vascular endothelial cells. The placenta protein and mRNA expression of HIF-1α and its target gene in the donor placenta increased significantly (P<0.001) compared with that in the control placenta, but the expression of HIF-1α and its target gene in the recipients tended to be similar in the controls (P>0.05). There was no difference between the controls. CONCLUSION: When the monochorionic twin placenta is formed in the early period, HIF-1α, VEGF and VEGFR-1 are over-expressed, which may affect the placenta angiogenesis and induce TTTS .

New fluorescence endoscope for use in twin-twin transfusion syndrome: in vivo visualization of placental blood vessels.

Twin-twin transfusion syndrome (TTTS) is a condition in which twins share blood disproportionately by the communicating vessels in the shared placenta, resulting in high fetal and perinatal mortality. Fetoscopic laser photocoagulation is performed to interrupt these communicating vessels; however, small vessels are often missed due to the poor image obtained with a fetoscope. We have developed a fluorescence endoscope capable of visualizing very small vessels, even in amniotic fluid, and we investigated its feasibility for in vivo visualization of placental vessels. Indocyanine green (ICG) was given at single doses of 0.5, 1.0, and 1.5 mg/kg, respectively, into the maternal circulation of pregnant rabbits, and the endoscope was used to identify the placental vessels. The vessels were detected within 15s after ICG injection for about 10 min. The brightness difference between the intervillous space and the umbilical vessels was significantly smaller after administration of 0.5 mg/kg than after 1.0 mg/kg (p=0.02) or 1.5 mg/kg (p=0.01). Even very small vessels (0.2mm in diameter) were detected. In conclusion, our new endoscope successfully provided a detailed view of the placental vessels in vivo. The results are promising for future TTTS laser surgery.

Clinical and biochemical predictors of very preterm birth in twin-to-twin transfusion syndrome treated by fetoscopy.

OBJECTIVE: To evaluate pre- and postoperative predictors of preterm birth in twin-to-twin transfusion syndrome treated with fetoscopic placental laser coagulation. STUDY DESIGN: Prospective cohort study (n = 166) assessing cervical length (pre and postoperatively), amniotic fluid interleukin-6, serum C-reactive protein and duration of surgery. Logistic regression was used to investigate associations with preterm delivery. RESULTS: Preterm delivery within 7 days, before 28.0 and 32.0 weeks occurred in 4.8%, 16.8%, and 28.9%, respectively. The only significant predictor of delivery within 7 days was postoperative cervical length (odds ratio [OR], 0.5; 95% confidence interval [CI], 0.3-0.9). Concerning delivery before 32.0 weeks, preoperative cervical length (OR, 0.9; 95% CI, 0.8-1.0), and gestational age (OR, 0.8; 95% CI, 0.4-0.9) were independent risk factors but the association was weak. The presence of a single survivor after surgery was associated with a clear reduction of risk (OR, 0.3; 95% CI, 0.1-0.6). Inflammatory biomarkers and duration of surgery did not discriminate risk of prematurity. CONCLUSION: No strong preoperative predictive factor of preterm birth could be identified. A single survivor was a strong protective factor of very preterm birth.

The relationship between amniotic fluid levels of brain-type natriuretic peptide and recipient cardiomyopathy in twin-twin transfusion syndrome.

OBJECTIVE: We sought to evaluate amniotic fluid brain natriuretic peptide (BNP) levels as a biomarker of recipient twin (RT) cardiomyopathy (RTCM) in twin-twin transfusion syndrome. STUDY DESIGN: Amniotic fluid samples were obtained from 157 twin-twin transfusion syndrome RTs and from 6 singletons (controls) from 2007 through 2009. N-terminal prohormone BNP (NT-proBNP) levels were quantified by enzyme-linked immunosorbent assay. RTCM was classified as mild (IIIA), moderate (IIIB), or severe (IIIC) by fetal echocardiography. The relationship between NT-proBNP and RTCM was evaluated using analysis of variance. The ability of NT-proBNP to predict moderate or greater RTCM was evaluated by receiver operating characteristic analysis. RESULTS: There is a significant positive correlation between NT-proBNP levels and worsening RTCM (r = 0.33; P < .001). NT-proBNP thresholds of 569 fmol/mg and 369 fmol/mg had a sensitivity of 70% and 87%, and specificity of 67% and 42%, respectively, in predicting moderate or greater RTCM. CONCLUSION: This is the first large case series that demonstrates a relationship between NT-proBNP and RTCM. This pathophysiologic insight supports ongoing efforts to develop screening biomarkers.

Segmental arterial mediolysis with accompanying venous angiopathy: a clinical pathologic review, report of 3 new cases, and comments on the role of endothelin-1 in its pathogenesis.

The authors review 20 cases of segmental arterial mediolysis (SAM) including 3 newly reported cases. SAM developed in areas of vascular distention in 2 of the latter cases: 1 in utero in the heart of a recipient of a twin transfusion syndrome and the other in the jejunum secondary to partial venous obstruction. In the third case, it occurred in a patient with Raynaud disease. Characterizing SAM are injurious and reparative lesions that occur in the media and/or at the adventitial medial junction. Four distinctive alterations are recognized: (1) mediolysis, (2) a tearing separation of the outer media from adventitia, (3) arterial gaps, and (4) a florid reparative response that replaces zones of mediolysis and fills areas of medial adventitial separation. The repair can transform SAM into lesions indistinguishable from common types of fibromuscular dysplasia (FMD.) A venous angiopathy involving large and medium-sized veins accompanies SAM. It features medial muscle vacuolar change with lysis leading to apparent separation of residual muscle bundles. Immunostaining shows endothelin-1 (ET-1) decorating adventitial capillaries in SAM and neighboring arteries, in capillaries of adjoining tissues, and outlining smooth muscle cell membranes in adjacent veins including those of the venous angiopathy. The significance of these changes is uncertain. Vasospasm is believed to cause SAM, but ET-1 is not the direct pressor agent responsible for this condition. The reason(s) for synthesis and release of ET-1 in SAM are still hypothetical, but local perturbations in vascular tone may be an important factor. ET-1 may be indirectly play a role in SAM by cross-talking and potentiating the activities of other vasoconstrictors such as norepinephrine and by orchestrating its reparative phase.

Regulation of amniotic fluid volume.

Water arrives in the mammalian gestation from the maternal circulation across the placenta. It then circulates between the fetal water compartments, including the fetal body compartments, the placenta and the amniotic fluid. Amniotic fluid is created by the flow of fluid from the fetal lung and bladder. A major pathway for amniotic fluid resorption is fetal swallowing; however, in many cases the amounts of fluid produced and absorbed do not balance. A second resorption pathway, the intramembranous pathway (across the amnion to the fetal circulation), has been proposed to explain the maintenance of normal amniotic fluid volume. Amniotic fluid volume is thus a function both of the amount of water transferred to the gestation across the placental membrane, and the flux of water across the amnion. Water flux across biologic membranes may be driven by osmotic or hydrostatic forces; existing data suggest that intramembranous flow in humans is driven by the osmotic difference between the amniotic fluid and the fetal serum. The driving force for placental flow is more controversial, and both forces may be in effect. The mechanism(s) responsible for regulating water flow to and from the amniotic fluid is unknown. In other parts of the body, notably the kidney, water flux is regulated by the expression of aquaporin water channels on the cell membrane. We hypothesize that aquaporins have a role in regulating water flux across both the amnion and the placenta, and present evidence in support of this theory. Current knowledge of gestational water flow is sufficient to allow prediction of fetal outcome when water flow is abnormal, as in twin-twin transfusion syndrome. Further insight into these mechanisms may allow novel treatments for amniotic fluid volume abnormalities with resultant improvement in clinical outcome.

Cord blood leptin and IGF-I in relation to birth weight differences and head circumference in monozygotic twins.

OBJECTIVES: To investigate a potential role of leptin and insulin-like growth factor (IGF)-I on fetal growth and metabolic function we determined plasma leptin and IGF-I concentrations in twins in relation to discordant fetal growth. STUDY DESIGN: In studying monochorionic twins with inter-twin birth weight difference, we investigated the relative contribution of genetic (fetus) versus environmental (maternal/placental) factors on growth. Thirty-six sets of twins (14 with discordant growth, birth weight difference >15%) who had been treated for severe twin-to-twin transfusion syndrome (TTTS) by laser coagulation were studied. Cord blood samples were collected at birth and analyzed for IGF-I and leptin. Inter-twin differences (delta) of birth weight and head circumference were correlated to delta hormone levels. RESULTS: An inter-twin correlation for leptin (r = 0.69; p <0.0001) and delta IGF-I (r = 0.49; p <0.0001) was found. delta birth weight correlated significantly with delta IGF-I (r = 0.67; p <0.0001) but not with delta leptin (r = 0.23; p = 0.19). delta IGF-I concentrations did not correlate with delta leptin (r = 0.18). delta head circumference correlated significantly with delta leptin (r = 0.47; p <0.01) and with delta IGF-I (r = 0.46; p <0.01). Using a multiple regression model with head circumference as dependent variable, adjusted for gestational age, head circumference remained significantly associated with higher leptin concentrations in all patients (p = 0.03). CONCLUSION: IGF-I is a good indicator for fetal growth and brain development. Leptin seems to be mainly genetically determined but may play a role in fetal brain development and is not only an index for fetal fat mass.