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The objective of this study was to evaluate the placental characteristics of monochorionic twin pregnancies with selective intrauterine growth restriction (sIUGR) classified according to the Gratacós classification based on umbilical artery Doppler measurements.All consecutive placentas from monochorionic twin pregnancies with sIUGR, (defined as a birthweight discordance25% and/or an estimated fetal weight in one twin10th centile) examined between May 2002 and February 2018 were included in the study. Each placenta was injected with colored dye to study the angioarchitecture. Primary outcomes were placental share discordance and diameter of the arterio-arterial anastomoses in relation to the umbilical artery Doppler types of sIUGR (Gratacós classification).Of the 83 sIUGR twins included, 27 were classified as Gratacós type I, 24 as type II and 32 as type III. The median gestational age at delivery was 34.3 weeks for type I, compared to 31.2 weeks and 31.6 weeks for type II and type III respectively. A trend towards a higher placental share discordance in type III sIUGR was observed. The median arterio-arterial diameter was 1.7 mm (0.8-2.6) in type I, 1.7 mm (1.2-2.2) in type II and 2.8 (2.0-3.5) mm in type III (p 0.01).Type III sIUGR placentas appear to be characterized by a larger diameter of the arterio-arterial anastomoses and a larger placental share discordance compared to type I and II sIUGR. The insights in the placental architecture of sIUGR placentas may offer new views on the pathophysiology of the disease.

To estimate the prevalence of velamentous cord insertion (VCI) in dichorionic (DC) and monochorionic (MC) twins with and without twin-twin transfusion syndrome (TTTS), and to study the associated outcomes.We recorded the type of umbilical cord insertion in all consecutive DC and MC placentas examined in two European tertiary medical centers. The association between VCI and perinatal outcomes was estimated and compared.A total of 1498 twin placentas were included in this study (DC placentas n = 550, MC placentas without TTTS n = 513 and MC placentas with TTTS n = 435). The prevalence of VCI in DC, MC without TTTS and MC with TTTS groups was 7.6%, 34.7% and 36.1%, respectively (P 0.001). In MC twins (non-TTTS and TTTS groups), VCI was associated with severe birth weight discordance (odds ratio [OR] 4.76 95% CI 2.43, 10.47 and OR 4.52 95% CI 1.30, 28.59, respectively). In MC twins without TTTS, VCI was associated with small for gestational age (OR 1.66, 95% CI 1.12, 2.50). VCI was significantly associated with increased risk of intrauterine fetal demise in MC twins, and this effect was greater in the non-TTTS group (OR 2.71 95% CI 1.38, 5.47). These associations did not occur in DC group. Gestational age at birth was lower in the presence of VCI in the DC and MC twins without TTTS.Our findings confirm that the prevalence of VCI is higher in MC twins than in DC twin pregnancies. VCI is an important indicator of adverse perinatal outcome, particularly in MC twins.

Introduction The aim of this study is to evaluate the prevalence of veno–venous (VV) anastomoses in a large cohort of monochorionic (MC) twin placentas with twin–twin transfusion syndrome (TTTS) compared to a control group of MC placentas without TTTS. Methods All TTTS placentas not treated with fetoscopic laser surgery (TTTS group) and examined at five international fetal therapy centers were included in this study and compared with a control group of MC placentas without TTTS (non-TTTS group). MC placentas were routinely injected with colored dye. We recorded the presence of VV and arterio-arterial (AA) anastomoses. Results A total of 414 MC placentas were included in this study (TTTS group, n = 106; non-TTTS group, n = 308). The prevalence of VV anastomoses was significantly higher in the TTTS group than in the non-TTTS group, 36% (38/106) and 25% (78/308), respectively (p = .04; odds ratio (OR) 1.65; 95% confidence interval (CI): 1.03–2.64). In the subgroup of MC placentas without AA anastomoses, the prevalence of VV anastomoses in the TTTS group and non-TTTS group was 32% (18/57) and 8% (2/25), respectively (p = .03; OR: 5.31; 95% CI: 1.13–24.98). Discussion VV anastomoses are detected more frequently in TTTS placentas than in MC placentas without TTTS and may thus play a role in the development of TTTS.

The introduction of the Solomon technique for the treatment of twin-twin transfusion syndrome (TTTS) increased placental exposure to laser energy. This study aims to identify the impact of power and energy used in laser treatment on placental tissue and pregnancy outcome.Pictures of all dye-injected placentas since the start of the Solomon trial were analyzed. Placental damage was scored using a grading system including visual scar depth and affected proportion of the vascular equator. Parameters analyzed included laser power and total energy, gestational age (GA) at laser, GA at birth, laser-to-delivery interval and preterm prelabor rupture of membranes (PPROM).We included 122 cases in the analysis. More placental damage occurred more often in the Solomon group (42%) compared to the selective group (15%) (p 0.001). In multivariate analysis, more placental damage was associated with higher laser energy (regression coefficient B 0.002) but not with higher power setting (regression coefficient B -0.442). More damage was associated with earlier GA at birth (regression coefficient B -0.167), higher incidence of PPROM32 weeks (regression coefficient B 0.003) and a shorter laser-to-delivery interval (regression coefficient B -0.168).Placental damage is positively associated with more laser energy but negatively associated with higher power setting. More placental damage was associated with a lower GA at birth, shorter laser-to-delivery interval and higher PPROM rate. Whether these results should lead to a change in surgical technique requires more research, both further ex-vivo experiments on human placentas and clinical studies.

The aim of this study was to investigate the independent role of veno-venous (VV) anastomoses in the development of twin-twin transfusion syndrome (TTTS). Thirty TTTS placentas and 41 non-TTTS placentas, routinely injected with colored dye, were enrolled in this study. We excluded all cases with arterio-arterial (AA) anastomoses and TTTS cases treated with laser surgery. The prevalence of VV anastomoses was significantly higher in TTTS cases compared to non-TTTS cases, 37% (11/30) and 7% (3/41), respectively (P.01; odds ratio 7.3; 95% confidence interval: 1.8-37.1). Our findings suggest that, in the absence of AA anastomoses, VV anastomoses may enhance the development of TTTS.

Fetoscopic laser coagulation of placental vascular anastomoses is considered to be the treatment of choice in severe twin-to-twin transfusion syndrome. The aim of fetoscopic laser surgery is to separate completely the inter-twin placental circulation. Incomplete laser coagulation may result in residual vascular anastomoses. The incidence and clinical implications of residual anastomoses in twin-to-twin transfusion syndrome treated with fetoscopic laser surgery has not yet been studied. We examined all placentas treated with fetoscopic laser surgery and delivered at our center between June 2002 and December 2005 with vascular injection using colored dyes. Presence of residual anastomoses was studied in association with adverse outcome and inter-twin hemoglobin difference at birth. Adverse outcome was defined as fetal demise, neonatal death or severe cerebral injury. The relation between residual anastomoses and placental localization (anterior or posterior uterine wall) was evaluated. A total of 52 laser-treated placentas were studied. Residual anastomoses were detected in 33% (17/52) of placentas. Adverse outcome was similar in the groups with and without residual anastomoses, 18% (6/34) and 29% (20/70), respectively (p=0.23). Large inter-twin hemoglobin differences (5g/dL) were found in 65% (11/17) of cases with residual anastomoses and 20% (7/35) of cases without residual anastomoses (p0.01). Anterior placental localization was not associated with a more frequent presence of residual anastomoses. In conclusion, residual anastomoses at our institution are seen in one-third of monochorionic placentas treated with fetoscopic laser surgery. Although residual anastomoses in our study were not associated with adverse outcome, they were often associated with neonatal hematological complications.

We performed a matched case-control study to analyze the placental angioarchitecture, in particular the diameter of arterio-arterial (AA) anastomoses in monochorionic placentas from pregnancies with twin-twin transfusion syndrome (TTTS) compared to a control group of uncomplicated monochorionic placentas. Placental angioarchitecture was analyzed using colored dye injection. AA anastomoses were detected in 37% (14/38) of TTTS placentas versus 91% (209/228) in control placentas (p < 0.001). The median diameter of AA anastomoses in the group with and without TTTS was 1.9 mm and 2 mm, respectively (p = 0.711). In conclusion, our findings show that AA anastomosis occur less frequently in TTTS placentas, supporting the concept of the protective role of AA anastomoses in TTTS. However, the size of the AA anastomosis, when present, does not appear to influence the pathophysiology of the disease.

We performed a matched caseecontrol study to analyze the placental angioarchitecture, in particular thediameter of arterio-arterial (AA) anastomoses in monochorionic placentas from pregnancies withspontaneous twin anemia-polycythemia sequence (TAPS) compared to a control group of uncomplicatedmonochorionic placentas. Placental angioarchitecture was analyzed using colored dye injection. AAanastomoses were detected in 20% (3/15) of spontaneous TAPS placentas. The median diameter of AAanastomoses in the group with and without TAPS was 0.4 mm and 2.2 mm, respectively (p ¼ 0.01). Inconclusion, AA anastomoses are rarely detected in TAPS placentas. When present, the AA anastomosis isvery small, preventing equilibration of hemoglobin levels between both twins. 2012 Elsevier Ltd. All rights reserved. 1. IntroductionFeto-fetal blood transfusion occurs in all monochorionic (MC)twins because of the invariable presence of placental vascularanastomoses and may lead to the development of twin anemia-polycythemia sequence (TAPS) [1]. TAPS is characterized by largeinter-twin hemoglobin differences in the absence of amniotic fluiddiscordances [1]. The typical angioarchitecture in TAPS placentasafter colored dye injection demonstrates only a few minusculearterio-venous (AV) anastomoses [2]. Arterio-arterial (AA) anasto-moses are reported to be rare (10%) in TAPS [1]. In contrast, AAanastomoses are almost ubiquitous in normal monochorionicplacentas [2], suggesting that AA anastomoses may play a protect-ing role against the development of TAPS [2].We previously hypothesized that the diameter of AA anasto-moses in TAPS may be smaller, preventing adequate inter-twinblood volume equilibration [3,4]. However, evidence to supportthis hypothesis is currently lacking. The objective of this study wasto compare the diameter of AA anastomoses in MC twin placentaswith and without TAPS.

In vivo measurements of blood flow through arterio-venous anastomoses in monochorionic twin placentas have recently been attempted with Doppler ultrasound, but the accuracy is questionable. We present a case of twin-to-twin transfusion syndrome treated with fetoscopic laser surgery. The ex-recipient subsequently became severely anaemic and was treated with an intrauterine blood transfusion at 29 weeks' gestation. After birth, a placental injection study identified residual unidirectional arterio-venous anastomoses from the ex-recipient to the ex-donor without arterio-venous anastomoses in the opposite direction. Prospective measurements of decreasing haemoglobin levels between the intrauterine transfusion and birth allowed us to assess the net blood flow through the anastomoses as 27.9 mL/24 h. This finding may also explain the inaccuracy of Doppler flow measurements, as such low flow velocities cannot possibly be detected with current Doppler techniques.

Introduction Most monochorionic (MC) twin pregnancies have an uncomplicated course, but some develop severe complications including selective intrauterine growth restriction (sIUGR), twintwin transfusion syndrome (TTTS) and twin anemia–polycythemia sequence (TAPS). The underlying pathogenesis of these various complications is associated with the ubiquitous presence of vascular anastomoses in MC placentas. Methods The aim of this study was to estimate the prevalence, number, size and localization of the anastomoses in sIUGR, TTTS and TAPS placentas compared to normal MC placentas using color dye injection. We excluded MC twin pregnancies treated with fetoscopic laser surgery or selective feticide. Results A total of 235 placentas fulfilled the inclusion criteria: 126 normal MC, 47 TTTS, 46 sIUGR and 16 spontaneous TAPS. Median number of anastomoses in normal MC, sIUGR, TTTS and TAPS placentas was 8 (IQR: 4–12), 8 (IQR: 5–14), 7 (IQR: 5–11) and 4 (IQR: 3–5), respectively. The prevalence of arterio-arterial (AA) anastomoses in normal MC, sIUGR, TTTS and TAPS placentas was 96%, 98%, 47% and 19%, respectively. We found AV anastomoses to be evenly distributed along the vascular equator in all MC placentas except in TAPS cases, where anastomoses were mostly localized near the margin. We also found that, in sIUGR and TTTS placentas, AA anastomoses tended to be at the center of the placenta. Conclusion The present study shows that the prevalence, size, number and localization of the various types of anastomoses differ between normal MC, sIUGR, TTTS and TAPS placentas.

Twin-to-twin transfusion syndrome (TTTS) is due to unbalanced inter-twin blood flow through placental vascular anastomoses. We present a TTTS-case treated with fetoscopic laser surgery that allowed us to calculate the net inter-twin blood flow. In the weeks following laser treatment, the ex-recipient developed severe fetal anemia and was treated with two intrauterine adult red cell transfusions (at 26 and 29 weeks' gestation, respectively). After birth, placental injection with color-latex identified a single residual arterio-venous anastomosis from the ex-recipient to the ex-donor. We measured the fetal and adult hemoglobin concentrations in the anemic fetus before and after both intrauterine transfusions, and in both twins at birth. On the basis of these measurements, we calculated the blood flow across the residual arterio-venous anastomosis and found it to be 5.8 +/- 1.5 mL/24 h after the 1st transfusion and 11.4 +/- 2.9 mL/24 h after the 2nd transfusion. (C) 2008 Elsevier Ltd. All rights reserved

Sequential laser therapy of twin–twin transfusion syndrome (TTTS) includes laser obliteration of arteriovenous (AV) anastomoses from donor to recipient (AVDR) before obliterating AV anastomoses from recipient to donor (AVRD). This strategy allows for a beneficial intra-operative transfusion of blood from the hypervolemic recipient to the hypovolemic donor. In the present study, we sought to analyze the benefits and risks of sequential laser therapy with our computational model to aid its more widespread introduction. We simulated an equally shared placenta with an AVDR and a smaller diameter AVRD causing TTTS at 20 weeks. Laser coagulation and various volumes and directions of inter-twin transfusion were simulated at 21 weeks. A typical result is that when an AVDR is coagulated first, and 10 min later the AVRD with inner diameter of about 1 mm, an inter-twin transfusion of 25 ml may result from the recipient to the donor, based on literature data of AV flow versus diameter. This procedure causes a simulated loss of 50% of the recipient's blood volume. The opposite coagulation sequence, thus coagulating the AVRD first, 10 min later followed by the AVDR of 1 mm inner diameter, causes a loss of the donor's blood volume of 64%. In conclusion, our simulations support the concept of sequential laser therapy for TTTS and suggest directions for an improved safety and efficacy of this strategy.

Background: The twin-to-twin transfusion syndrome (TTTS) is a severe complication of monochorionic twin pregnancies, caused by a net inter-twin transfusion of blood from one fetus (the donor) towards the other fetus (the recipient) through placental anastomoses. TTTS is driven by unidirectional-arterio-venous anastomoses, and mitigated by bidirectional arterio-arterial or veno-venous anastomoses which reduce the net inter-twin transfusion. In contrast to these accepted concepts, cases have been described paradoxically devoid of arterio-venous anastomoses but including arterio-arterial anastomoses. We hypothesized that TTTS may develop in such cases as a consequence of a stenosed chorionic artery in the recipient placenta that connects with the arterio-arterial anastomosis.Clinical cases: We describe two cases of monochorionic twin placentae without arterio-venous anastomoses but with only an arterio-arterial and veno-venous anastomosis. In one case severe TTTS developed. There, the arterio-arterial anastomosis connected to a stenosed chorionic artery in the recipient placenta and showed a tortuous appearance. The other case developed uneventful. It lacked a stenosed chorionic artery and the arterio-arterial anastomosis was non-tortuous.Conclusion: We present evidence that the arterio-arterial anastomosis represented a functional collateral artery whose outgrowth was driven by an increased shear-stress caused by an increased flow to a lower pressure vascular bed in the placenta of the recipient. The lower arterial pressure occurred from the moment that a chorionic artery which was connected to the anastomosis developed a significant stenosis. The resulting collateral flow through the anastomosis maintained blood supply to the lower pressure placental bed, the beneficial function of collaterals, but also resulted in an increasing net inter-twin transfusion which triggered onset of severe TTTS. (c) 2007 Elsevier Ltd. All rights reserved.

Placental vascular anastomoses in monochorionic twins may lead to acute or chronic inter-twin transfusion. We report an uncommon form of chronic inter-twin transfusion, referred to as twin anemia-polycythemia sequence (TAPS), with severe anemia in one twin and polycythemia in the other, without the characteristically associated twin oligo-polyhydramnios sequence (TOPS) seen in the classical twin-to-twin transfusion syndrome (TTTS). The clinical course and placental characteristics of two pairs of monochorionic twins with TAPS born at, respectively, 33 and 34 weeks' gestation were reviewed. Serial fetal ultrasound examinations revealed no signs of TOPS. At birth, both donor twins were severely anemic requiring blood transfusion and both recipients were polycythemic, one requiring partial volume exchange transfusions. Inter-twin difference in reticulocyte counts was extremely high, suggesting a chronic form of inter-twin blood transfusion. Placental injection studies revealed a preponderance of very small (