Ultrasound assessment of venous blood flow before and after laser therapy: approach to understanding the pathophysiology of twin-twin transfusion syndrome

Ultrasound measurement of umbilical venous flow volume at the intra-abdominal portion in normal fetuses

PURPOSE

Umbilical venous flow volume (UVFV) measured using ultrasound can be used to assess placental circulation in a fetus. UVFV measured at the intra-abdominal portion using half the maximum flow velocity of the umbilical vein (UV) has good reproducibility with low variance. However, reference values in previous reports were based on a small number of cases with a wide reference range. In the present study, we evaluated UVFV standard values measured at the intra-abdominal portion in normal Japanese fetuses.

METHODS

Measurements were performed on normal pregnant women during routine ultrasound screening at around 20 or 30 weeks of gestation. The diameter and flow velocity of the UV were measured at the fetal abdomen point between the insertion of the UV and branches of the portal vein. UVFV (ml/min) was calculated as follows: (UV diameter [cm]/2)2 × maximum velocity [cm/s] × 0.5 × 3.14 × 60).

RESULTS

A total of 278 pregnant women were included in the study. UVFV increased with gestational weeks, and UVFV per estimated fetal weight (EFW) slightly decreased with increasing gestational weeks. The 50th (10th-90th) percentiles of UVFV per EFW at 20, 25, and 30 weeks of gestation were 130 (105-165), 123 (94-147), and 104 (80-131) ml/min/kg, respectively.

CONCLUSION

New UVFV reference values measured at the intra-abdominal portion of fetuses using large-scale samples were established. Future studies should assess fetuses under pathologic conditions using UVFV reference values.

Correction of fetal umbilical vein flow imbalance following laser surgery for twin-twin transfusion syndrome

OBJECTIVES

Twin-twin transfusion syndrome (TTTS) is characterized by unequal hemodynamics between the twins. We aimed to assess preoperatively the difference in umbilical vein flow (UVF) between the recipient and donor monochorionic diamniotic twins and evaluate the change in UVF following laser surgery in both twins.

METHODS

This was a retrospective cohort study of differences in UVF that occurred following laser surgical treatment of TTTS. Sonographic assessment of the umbilical vein before and 24 h after fetoscopic laser surgery for TTTS was performed. Umbilical vein diameter and time-averaged maximum velocity were measured, and UVF per kg (UVF/kg) was converted into a Z-score by a calculator created using gestational age as an independent variable. Z-score values were converted into centiles, which were evaluated statistically. Median differences in UVF/kg centile values were adjusted for TTTS stage and presence of arterioarterial anastomoses.

RESULTS

The study population consisted of 363 TTTS patients. The adjusted preoperative median difference in UVF/kg centile between the recipient vs donor twin was 17.9% (-17.1% to 57.6%), P < 0.0001. The adjusted median difference in UVF/kg centile between the postoperative vs preoperative period among recipients was 2.2% (-10.8% to 13.8%), P < 0.0001, while the adjusted median difference among donors was 27.3% (8.2%-34.6%), P < 0.0001.

CONCLUSION

The preoperative difference in UVF between the recipient and donor twins confirms the pathophysiology of TTTS. Postoperatively, the substantial increase in UVF of the donor twin and the relatively small increase in UVF of the recipient twin confirm that ablation of the vascular communications resulted in rapid improvement in perfusion of the donor twin. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Sonographic evaluation of umbilical cord thickness in monochorionic diamniotic twin pregnancies

OBJECTIVE

To develop a nomogram of the thickness of the umbilical cord (UC) and its components in monochorionic diamniotic (MCDA) twin pregnancies.

METHODS

This prospective longitudinal study involved 47 MCDA twin pregnancies (94 fetuses) between 18 and 33 weeks of gestation. Ultrasound assessments of UC cross-sections and measurements of the umbilical cord area (UCA), the umbilical vein area (UVA), the umbilical artery area (UAA), and the Wharton jelly area (WJA) were made. The UC measurements were correlated with gestational ages. Reference values for the gestational ages of MCDA pregnancies were determined and compared with those of dichorionic twins and singletons. The cases which developed selective intrauterine growth restriction were contrasted with normal cases.

RESULTS

A positive correlation was found between all UC components and gestational age and fetal weight. The UCA of MCDA fetuses was significantly larger than that of DC fetuses (P < 0.001) at the expense of a larger WJA (P < 0.001) and similar to that of singleton pregnancies. The MCDA fetuses with an estimated fetal weight below the 10th percentile had a smaller UCA than fetuses with a normal estimated weight (P < 0.001).

CONCLUSION

The MCDA twins exhibited a thicker UC than that of dichorionic twins. This article is protected by copyright. All rights reserved.

Management of atypical cases of twin-to-twin transfusion syndrome

Up to 20% of monochorionic diamniotic twin pregnancies can be complicated with twin-to-twin transfusion syndrome (TTTS). This complication is diagnosed by ultrasound demonstrating amniotic fluid discordance between both amniotic sacs, with polyhydramnios in the recipient's sac and oligohydramnios in the donor's, secondary to an imbalance in blood volume exchange between twins. Ultrasound evaluation of the amniotic fluid volume, bladder filling, and assessment of fetal Doppler parameters provide the basis for classification of TTTS, allowing severity assessment. The Quintero's staging system provides a standardized prenatal estimate on the risk of intrauterine fetal demise of one or both twins and the need for fetoscopic laser coagulation of placental vascular anastomoses or delivery depending on the gestational age. However, a proportion of TTTS cases may present without a linear progressive deterioration and no ultrasound signs of preceding staging, in rare situations, they arise even without amniotic fluid discordance. Thus, these unusual clinical presentations of TTTS have long been grouped into the category of atypical TTTS. In this review, we show the clues for diagnosis and management of different atypical cases of TTTS highlighting their underlying mechanism to improve the clinical understanding of such atypical situations, avoid misdiagnosis of TTTS, and allow a timely referral to a fetoscopic center.

Evaluation of umbilical venous flow volume measured using ultrasound compared to circuit flow volume in the EXTra-uterine Environment for Neonatal Development (EXTEND) system in fetal sheep

OBJECTIVE

To compare and validate umbilical venous flow volume (UVFV) measured at the intra-abdominal portion using ultrasound with actual flow volume of umbilical vein (UV) in fetal sheep sustained on the EXTrauterine Environment for Neonatal Development (EXTEND) system.

METHODS

Circuit flow volume through the oxygenator was obtained using sensors. Ultrasound derived UVFV (ml/min) was calculated as (UV diameter [cm]/2)² × 3.14 × maximum velocity (cm/s) × 0.5 × 60, measured at approximately the mid portion between its abdominal insertion and the origin of the ductus venosus. UVFV was measured by ultrasound once daily and was compared to the average of daily circuit flow volume directly measured.

RESULTS

UVFV was measured 168 times in 15 fetal sheep. The ratio of circuit flow volume to combined cardiac output remained stable within the anticipated physiological range throughout. UVFV measured by ultrasound showed good correlation to directly measured circuit flow (r = 0.72). Interclass correlation coefficients for intra-observer variability was 0.991 (95% confidence interval [CI], 0.979-0.996).

CONCLUSION

UVFV measured at the intra-abdominal portion using ultrasound shows a good correlation with directly measured circuit flow volume in UV of fetal sheep on the EXTEND system. Regular incorporation of such validated UVFV measures into clinical use may offer opportunities to better understand conditions of placental dysfunction.

Reliability and characteristics of ultrasound measurement of fetal umbilical venous blood flow volume according to the site of measurement

PURPOSE

This study aimed at assessing the reliability and characteristics of fetal umbilical venous blood flow volume (UVFV) measurement using ultrasound.

METHODS

We conducted a prospective study at our center from November 2017 to July 2019. We performed transabdominal ultrasound examinations at 18-34 weeks' gestation in uncomplicated singleton pregnancies. UVFV was calculated using vessel diameter (D) and maximum flow velocity (V) as follows: (D/2)² × π × V × 0.5 × 60 (Q, mL/min). Two examiners measured each value three times in the free-loop (FL) and intra-abdominal (IA) portions of the umbilical vein. Intra-rater and inter-rater reliability was evaluated by intraclass correlation coefficient (ICC) and a Bland-Altman plot.

RESULTS

Two hundred and eight cases were measured by two examiners. The rate of complete measurement at FL and IA was not significantly different (88.5% vs. 79.3%, respectively; p = 0.113). The intra-rater reliability of D and V was high at FL and IA. Regarding inter-rater reliability, the ICC of D, V, and Q was 0.973, 0.582, and 0.963 at FL, and 0.994, 0.912, and 0.989 at IA, respectively. A Bland-Altman plot showed that D and V had greater standard deviation at FL than IA. Regarding Q, the standard deviation at FL was also larger than at IA, and measurement variance at FL increased as the measured value increased, but that at IA did not.

CONCLUSION

UVFV measurement showed high intra-rater and inter-rater reliability at FL and IA, but the variance of measurements at FL became large as the measured value increased. Properties of different measurement sites should be considered when evaluating UVFV.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

Ultrasound prognostic factors after laser surgery for twin-twin transfusion syndrome to predict survival at 6 months

OBJECTIVE

To evaluate the significance of ultrasound findings, detected one or two weeks after laser surgery for twin-twin transfusion syndrome, in predicting the mortality at 6 months of age.

METHODS

Ultrasound evaluation including fetal biometry, amniotic fluid volume estimation and Doppler examination was performed between 7 and 14 days after surgery for 181 cases. The presence of one or more effusions and single fetal death were also determined. Associations between ultrasound findings and mortality at 6 months of age were evaluated using multiple logistic regression analysis.

RESULTS

Of the total 181 pairs, 145 (80.1%) donor and 160 (88.1%) recipient twins survived in utero for more than 7 days after surgery, and hence were included in the analysis. The survival rate at 6 months was 66.9% for the donor and 80.7% for the recipient twins. Risk factors for death in the donor were the presence of severe intrauterine growth restriction and effusions. In recipients, elevation in the middle cerebral artery peak systolic velocity coincided with fetal death, but this occurred in only three cases.

CONCLUSION

Ultrasound risk factors one week after surgery included severe intrauterine growth restrictions and effusions in the donor twins.

Changes in umbilical venous volume flow after fetoscopic laser occlusion of placental vascular anastomoses in twin-to-twin transfusion syndrome

OBJECTIVE

To examine effects of fetoscopic laser occlusion of placental vascular anastomoses on umbilical venous volume flow in twin-to-twin transfusion syndrome.

STUDY DESIGN

Absolute umbilical venous volume flow, measured preoperatively and 48 hours after fetoscopic laser occlusion was related to Doppler studies, bladder filling in donors, and anastomoses.

RESULTS

Among 45 patients, recipients had decreased ductus venosus pulsatility index (ductus venosus-pulsatility index for veins, 1.16 vs 1.01; P < .001) and unchanged umbilical venous volume flow after fetoscopic laser occlusion (74.7 vs 74.5 mL; P = .407). Donors had decreased umbilical artery pulsatility (1.34 vs 1.11; P = .008), increased ductus venous-pulsatility index for veins (0.75 vs 0.91; P < .014), and significantly increased umbilical venous volume flow per kilogram by 52.3% (136.6 vs 208.0 mL/Kg/min; P < .001). Donor bladder filling occurred at higher umbilical venous volume flow per kilogram (142.7 vs 221.4 mL/Kg/min; P < .012). Increase in umbilical venous volume flow per kilogram correlated with the net difference in arteriovenous anastomoses (Pearson r = 0.403, P = .006).

CONCLUSION

Fetoscopic laser occlusion in twin-to-twin transfusion syndrome corrects intertwin differences in umbilical venous volume flow by predominant effects in the donor. Reappearance of donor bladder filling correlates with correction of volume flow.

In utero fetal oximetry via visible light spectroscopy in twin-twin transfusion syndrome

OBJECTIVE

The purpose of this study was to assess fetal tissue venous oxygenation (StO2%) in utero during laser therapy for twin-twin transfusion syndrome via visible light spectroscopy (VLS).

STUDY DESIGN

StO2% was measured in 10 donor and recipient twins at the level of the skin and placenta before and after laser therapy (SLPCV).

RESULTS

Pre-SLPCV skin StO2% was significantly lower in the donor than in the recipient twin (21.6 +/- 6.2 vs 31.2 +/- 8.6, respectively; P = .01), but the difference disappeared after SLPCV. Placental surface StO2% measurements in 5 patients showed a significant increase in StO2% in the territory of the recipient (P = .04). Preoperative linear streaming as evidence of nonadmixing deoxygenated and oxygenated blood disappeared after SLPCV.

CONCLUSION

In utero StO2% measurement is possible with VLS. Donor twins can have significantly less StO2% than recipient twins, but this is corrected after SLPCV. Further studies are warranted to determine the value of in utero VLS oximetry.

Validation of Quintero stage III sub-classification for twin-twin transfusion syndrome based on visibility of donor bladder: characteristic differences in pathophysiology and prognosis

OBJECTIVE

To validate the Quintero stage III subclassification for twin-twin transfusion syndrome (TTTS) based on visibility of the bladder of the donor twin.

METHODS

Between July 2002 and August 2006, there were 131 pregnant Japanese women affected by severe TTTS before 26 weeks' gestation, treated with fetoscopic laser surgery at five centers in Japan, whose pregnancies continued beyond 22 weeks. Outcome data were available in all cases and surviving infants were followed up for at least 6 years. This study focused on the Stage III TTTS patients. These were subclassified into Stage III atypical (abnormal Doppler flow with visible donor bladder) and Stage III classical (abnormal Doppler flow with non-visible donor bladder) groups. Perioperative data and postnatal outcomes were compared between the groups.

RESULTS

Seven Stage I, 22 Stage II, 82 Stage III and 20 Stage IV pregnancies continued beyond 22 weeks. There was a significantly higher incidence of absent or reversed end-diastolic velocity in the umbilical artery (UA-AREDV) of the donor in Stage III atypical than in Stage III classical patients (83.8% vs. 53.3%, P = 0.004). Stage III atypical cases also had a significantly higher incidence of arterioarterial (AA) anastomoses (72.9% vs. 17.8%, P < 0.001) and intrauterine fetal demise (IUFD) of the donor (43.2% vs. 13.3%, P = 0.002). However, there were no differences in overall survival or in abnormal brain scans of surviving infants. Donors with both UA-AREDV and AA anastomoses had a significantly higher incidence of IUFD compared with the others (53.3%, P < 0.001).

CONCLUSIONS

Quintero stage III atypical was characterized by a high incidence of AA anastomoses and UA-AREDV of the donor, resulting in IUFD. Subclassification of Stage III based on visibility of the bladder of the donor twin was adequate for and compatible with differentiating prognosis and pathophysiology.

Umbilical venous volume flow in twin-twin transfusion syndrome

OBJECTIVES

To examine umbilical venous volume flow (UVF) dynamics by twin status and disease severity in untreated twin-twin transfusion syndrome (TTTS).

METHODS

In 70 cases of untreated TTTS, absolute UVF, UVF corrected for estimated fetal weight (UVF/kg), intertwin difference (DeltaUVF/kg) and recipient to donor ratio (R/D-UVF/kg) were calculated. Parameters for UVF were compared with respect to twin status and disease severity (early, Quintero Stages I and II; advanced, Stages III and IV).

RESULTS

UVF/kg was higher in recipients than in donors and decreased with advancing stage in both twins (in recipients, 183.9 mL/kg/min vs. 145.6 mL/kg/min, P = 0.043; in donors, 137.5 mL/kg/min vs. 122.5 mL/kg/min, P = 0.033). Linear regression analysis demonstrated that the overall best correlation coefficient for DeltaUVF/kg was obtained for the Doppler pulsatility index of the umbilical artery (t = - 4.536, P < 0.001). In advanced stage, absolute and weight-corrected UVF were lower overall, while significant differences in intertwin volume flows persisted. The lowest flows were observed in hydropic recipients (median, 67.0 (range, 55.2-122.0) mL/kg/min vs. 180.8 (range, 59.1-565.4) mL/kg/min; P = 0.001).

CONCLUSIONS

In TTTS, UVF is significantly higher in recipients than in donors. With progression to advanced stage UVF/kg decreases in both twins as the magnitude of UVF that can be accommodated by the recipient declines. Further study of these dynamics in combination with cardiac performance parameters is warranted to refine diagnostic and prognostic assessment.

Fetal cardiac output in monochorionic twins

OBJECTIVES

To compare fetal cardiac output (CO) in donor and recipient twins of twin-twin transfusion syndrome (TTTS) pregnancies after laser therapy with that of monochorionic twins without TTTS and normal singletons.

METHODS

In a longitudinal, prospective study, we sonographically assessed fetal CO in donors (n = 10) and recipients (n = 10) with TTTS after fetoscopic laser therapy, in monochorionic twins without TTTS (n = 20) and in normal singleton pregnancies (n = 20). The fetal CO of TTTS twins was determined 1 day and 1 week after laser treatment, and from then on every 2-4 weeks until birth. Twins without TTTS were examined biweekly until birth. Singletons were examined twice, with an 8-week interval, at different gestational ages between 17 and 35 weeks.

RESULTS

Absolute CO increased exponentially with advancing gestational age (P < 0.0001), and was significantly related to fetal weight in all groups (P < 0.0001). The median CO/kg in donors after laser therapy, recipients after laser therapy and non-TTTS monochorionic twins was significantly higher than that in singletons (all P < 0.001). Median CO/kg in donors after laser therapy, recipients after laser therapy, and non-TTTS monochorionic twins was not significantly different between groups.

CONCLUSIONS

Monochorionic twins with TTTS have higher CO after laser therapy than normal singletons.

General vs local anesthesia for the percutaneous laser treatment of twin-twin transfusion syndrome

OBJECTIVE

The purpose of this study was to review our anesthetic experience in selective laser photocoagulation of communicating vessels (SLPCV) to treat twin-twin transfusion syndrome (TTTS).

STUDY DESIGN

A total of 266 consecutive eligible patients were studied. Twenty-seven patients (10%) underwent general anesthesia (GenA), 100 (38%) received total intravenous anesthesia (TIVA), and 139 (52%) received local anesthesia/conscious sedation (LocA). Maternal-fetal hemodynamic fluctuations were compared between groups.

RESULTS

Maternal blood pressure decreased significantly in all 3 groups during surgery (P < .0001) but was more evident in the GenA and TIVA groups (P < .0001). Maternal heart rate varied significantly in GenA (P = .02) but was constant in LocA and TIVA. There were no significant differences in fetal heart rate changes between the groups. Intraamniotic bleeding occurred more frequently with GenA and TIVA than LocA(P < .0001).

CONCLUSION

Local anesthesia is the safest anesthetic technique for SLPCV in TTTS patients.

Fetal growth after laser therapy for twin-twin transfusion syndrome

OBJECTIVE

The objective of the study was to compare twin weight discordance and prevalence of intrauterine growth restriction (IUGR) before laser therapy and after birth in pregnancies complicated by twin-twin transfusion syndrome (TTTS).

STUDY DESIGN

Women with TTTS who underwent laser therapy with dual neonatal survivors born at least 28 days after surgery were studied. Estimated fetal weight (EFW) discordance at the preoperative sonogram and birthweight (BW) discordance were calculated. Weights below gestational age-corrected 10th percentile at sonogram and at birth for each twin were designated as IUGR.

RESULTS

Among 211 women studied, the mean EFW discordance measured 26.6% and mean BW discordance was 18.4%, yielding a mean 8.2% decrease in weight discordance (P < .001). Comparing IUGR diagnoses before surgery and at birth, the recipient's proportion was unchanged (9.5% vs 7.1%, P = .353), whereas the donor's proportion decreased (64.5% vs 28.9%, P < .001).

CONCLUSION

Twin weight discordance and donor fetus IUGR appear to improve after laser therapy for TTTS.

The effect of fetoscopic laser therapy on fetal cardiac size in twin-twin transfusion syndrome

OBJECTIVES

To evaluate the influence of fetoscopic laser therapy on fetal cardiac size in monochorionic twins complicated by twin-twin transfusion syndrome (TTTS).

METHODS

In a longitudinal, prospective study, we assessed fetal cardiac size sonographically in monochorionic diamniotic twins with TTTS treated by laser therapy and in monochorionic twins without TTTS. The fetal cardiothoracic ratio (cardiac circumference divided by thoracic circumference) of TTTS twins was determined within 24 h before, 12-24 h after and 1 week after laser treatment, and from then on every 2-4 weeks until birth. TTTS twins were classified into Quintero Stages 1-2 (n = 18) and Stages 3-4 (n = 16), and measurements were compared with biweekly measurements of non-TTTS monochorionic twins matched for gestational age (n = 38). Cardiomegaly was defined as a cardiothoracic ratio above the 97.5th percentile.

RESULTS

Before laser treatment, cardiomegaly was observed in 44% (8/18) and 50% (8/16) of recipients in Quintero Stages 1-2 and Stages 3-4, respectively. Cardiomegaly occurred in none of the donors before treatment. After laser treatment, cardiomegaly was observed in 76% (13/17) and 50% (7/14) of recipients in Stages 1-2 and Stages 3-4, respectively, and in 17% (3/18) and 13% (2/15) of donors in Stages 1-2 and Stages 3-4, respectively. Cardiomegaly was present in 18% (7/38) and 8% (2/25) of non-TTTS monochorionic twins and singletons. After laser therapy, the cardiothoracic ratio of recipients in Stages 1-2 and Stages 3-4 was not significantly changed (P = 0.34 and P = 0.67, respectively). The cardiothoracic ratio of donors in Stages 1-2 and Stages 3-4 was increased compared with that before laser therapy (P = 0.0002 and P = 0.005, respectively). Cardiothoracic ratios of non-TTTS monochorionic twins were not significantly different from our reference range in singletons throughout gestation, and were smaller than those in both recipients and donors after laser therapy.

CONCLUSIONS

TTTS recipients show cardiomegaly before as well as after fetoscopic laser therapy for TTTS. Donors develop cardiomegaly only after laser treatment. Our findings emphasize the significant effect of TTTS and fetoscopic laser therapy on the fetal heart of both recipient and donor twins.

Three-dimensional sonographic assessment of fetal urine production before and after laser surgery in twin-to-twin transfusion syndrome

OBJECTIVE

Fetal urine production in twin-to-twin transfusion syndrome (TTTS) reflects the hemodynamic imbalance between the donor and recipient twins but it has not been measured in this particular condition. The aim of this study was to measure fetal urine production using three-dimensional (3D) ultrasound in donor and recipient twins before and after laser treatment for TTTS and to correlate this with umbilical venous volume flow (UVVF).

METHODS

Urine production rate (UPR) was measured using 3D ultrasound with Virtual Organ Computer-aided AnaLysis (VOCAL) in 106 cases of severe TTTS. The rotation angle was set at 30 degrees . The bladder volume was measured twice in each fetus (V(1) and V(2)), with an interval of 5-30 min between measurements, in order to calculate the UPR. When V(2) > V(1), UPR was calculated using the formula: V(2) - V(1) /time interval. Together with UPR, UVVF was measured before and after treatment. Both parameters were corrected for fetal weight. Inter- and intraobserver variability were calculated in 16 cases using the intraclass correlation coefficient.

RESULTS

Before laser treatment, UPR was significantly higher in recipients compared with donors (median, 14.8 and 0 mL/h/kg, mean 23.8 and 2.3 mL/h/kg, respectively, P < 0.001), and UPR was positively correlated with UVVF in both twins. Following laser treatment (48 h later), UPR decreased to 9 mL/h/kg (P < 0.001) in recipients, while there was no change in donors. UVVF increased significantly from a median value of 92 to 132 mL/min/kg (P < 0.01) in donors and decreased significantly from 150 to 99 mL/min/kg (P < 0.001) in recipients.

CONCLUSIONS

In TTTS UPR is correlated to UVVF and reflects the hemodynamic imbalance between donor and recipient twins. Following laser treatment, UPR decreases in recipients but is unaffected in donors. However, changes in UVVF occur in both twins. This suggests that although fetal renal function is driven by fetal hemodynamics, there may be a lag in the recovery of renal function in the donor twin.

Intertwin discordance in umbilical venous volume flow: a reflection of blood volume imbalance in twin-to-twin transfusion syndrome

OBJECTIVES

To compare umbilical venous volume flow (UVVF) between donor and recipient twins in twin-to-twin transfusion syndrome (TTTS) using an index that is independent of gestational age and to correlate changes in this index with outcome following endoscopic laser surgery.

METHODS

UVVF was calculated in 84 cases of TTTS by multiplying the umbilical vein cross-sectional area at its entry into the fetal abdomen by time averaged blood velocity. All cases were classified according to the Quintero staging system. The ratio between UVVF in recipients and donors (R/D-UVVF) in each pair of twins was calculated before and 48 h after laser treatment, and changes in R/D-UVVF were correlated with pregnancy outcome. Intraobserver and interobserver UVVF measurement reliability was assessed in 19 singletons, and 13 donor and recipient twins before laser treatment using the intraclass correlation coefficient (ICC).

RESULTS

Twenty-five, 32, 21 and six cases presented as Quintero Stages 1, 2, 3 and 4, respectively, at a median gestational age of 20 (range, 15-26) weeks. Intraobserver and interobserver ICC for UVVF measurement in twins were 0.97 and 0.67, respectively. UVVF was a median of 2.13-fold (range, 0.3-19-fold) higher in recipients than in donors (137 mL/min vs. 64 mL/min, P < 0.001) and increased with gestational age (r = 0.58, P < 0.001 for recipients, r = 0.62, P < 0.001 for donors). From 68 cases in which R/D-UVVF could be measured 48 h following laser surgery, cases with a favorable outcome showed a significant decrease in R/D-UVVF from a median of 1.97 to 1.27 (P < 0.01) and cases with recurrent TTTS (n = 6) did not (decrease in R/D-UVVF from a median of 2.32 to 2.19, P = 0.17). Using a cut-off of < 30% reduction of R/D-UVVF, 66% of the cases with recurrence could be predicted, and the odds ratio for recurrence was 3.13 (95% CI, 0.52-18.29). A significant UVVF imbalance between recipient and donor twins was found in cases with Quintero Stages 1-3 but not in those with Stage 4.

CONCLUSIONS

In TTTS, UVVF is significantly higher in recipients than in their donor cotwins and the R/D-UVVF seems adequately to indicate the flow imbalance between twins, regardless of gestational age. A decrease in R/D-UVVF could be predictive of a favorable evolution following laser treatment.

Twin-Twin Transfusion Syndrome Modeling

The twin-twin transfusion syndrome (TTTS) is a severe complication occurring in monochorionic twins, and untreated, causes high rates of mortality and morbidity. In TTTS, five consecutive stages of increasing severity can be distinguished: first, the oligopolyhydramnios sequence; second, anuria in the donor twin; third, abnormal flow waves in either twin; fourth, a hydropic recipient, and finally the fifth stage, fetal demise of either twin. Recently, we developed a mathematical model of the Stages I-IV. In this report, we investigated the influence of amnioreduction and laser therapy at two different gestational ages on the resolution of TTTS Stage III. Simulations were performed for two gestational ages, at 22 and 28 weeks; that is, at the onset of a stuck donor twin and when TTTS has progressed to an anuric donor with abnormal umbilical flow waves and a hydropic recipient, respectively. Results indicate abnormal umbilical flow waves in the donor to resolve rapidly after both amnioreduction and laser therapy. TTTS and abnormal umbilical flows in the donor, however, return after amnioreduction. Laser therapy, leading to cessation of fetofetal transfusion, produces complete resolution of TTTS sequelae, however, with increased vascular stiffness in the donor. Amnioreduction and laser therapy both produce rapid resolution of abnormal umbilical flows in a mathematical model of TTTS. Laser ablation of all anastomoses, however, completely ceases the fetofetal transfusion, so that no TTTS redevelops. In the donor, vascular stiffness remains increased after laser, suggesting increased pulse wave velocities can be measured clinically.

Ultrasound Assessment prior to Laser Photocoagulation for Twin-Twin Transfusion Syndrome for Predicting Intrauterine Fetal Demise after Surgery in Japanese Patients

OBJECTIVE

To evaluate the use of ultrasound before selective laser photocoagulation of communicating vessels (SLPCV) for twin-twin transfusion syndrome in predicting intrauterine fetal demise (IUFD).

METHODS

Fifty-five patients underwent SLPCV in Japan. Fetal biometry and Doppler studies of the umbilical artery, ductus venosus, and umbilical vein were performed prior to SLPCV. The visualization of the bladder and hydrops was recorded. Association between the parameters and IUFD was analyzed using multiple logistic regression analysis. The study was approved by the Institutional Review Board and patients gave their informed consent.

RESULTS

The IUFD incidence was 25.5% (14/55) in the donors and 12.7% (7/55) in the recipients. Twelve donors and 4 recipients of them ended in unexplainable IUFD. In the analysis of 53 donors, absent or reversed end-diastolic flow of umbilical artery (UAAREDF) was only associated with IUFD (p = 0.016). No parameters could predict IUFD in 52 recipients.

CONCLUSIONS

UAAREDF may be useful for predicting IUFD of the donor after SLPCV.

Stage-dependent fetal umbilical blood flow changes induced by laser therapy and amniodrainage in twin-to-twin transfusion syndrome

OBJECTIVE

To estimate changes in umbilical blood flow (UBF) and Doppler indices in pregnancies complicated by twin-to-twin transfusion syndrome (TTS) treated with either laser therapy or amniodrainage, and to evaluate the influence of the presence of hemodynamic deterioration prior to therapy, as determined by the Quintero stages of severity.

METHODS

Forty-eight cases of TTS were included, and further classified into severity Stages I or II (absence of critically abnormal Dopplers (CAD), n = 22) and Stages III or IV (presence of CAD or hydrops fetalis, n = 26). In Stages I-II, 14 cases were treated with laser and eight with amniodrainage, and in Stages III-IV, 17 were treated with laser and nine with amniodrainage. Differences in the UBF, umbilical artery pulstility index (UA-PI) and ductus venosus pulsatility index (DV-PI) were estimated for both groups of severity before and after both treatments. Eleven normal monochorionic pregnancies were evaluated as controls.

RESULTS

In recipients, UBF was significantly higher with respect to controls regardless of the stage, while donors had a significant decrease in UBF, but only in Stages III-IV. After laser treatment no changes were observed in fetuses in Stages I-II. In Stages III-IV, recipients showed a significant reduction in the DV-PI (mean DV-PI 1.31 +/- 0.18 vs. 1.05 +/- 0.22; P = 0.005) whereas donors showed a significant increase in the UBF (mean UBF 134 +/- 36 mL/min vs. 195 +/- 25 mL/min; P < 0.001) and in the DV-PI (mean DV-PI 0.99 +/- 0.26 vs. 1.36 +/- 0.42; P = 0.002), and a reduction in the UA-PI (mean UA-PI 1.86 +/- 0.41 vs. 1.58 +/- 0.30; P = 0.01). After amniodrainage only donor fetuses in Stages III-IV showed an increase in UA-PI (mean UA-PI 1.54 +/- 0.35 vs. 1.72 +/- 0.40; P = 0.015). No other changes were observed in any of the parameters studied.

CONCLUSION

Laser therapy induces consistent hemodynamic variations in TTS mainly manifested in Stages III-IV.

The role of laser surgery in dissecting the etiology of absent or reverse end-diastolic velocity in the umbilical artery of the donor twin in twin-twin transfusion syndrome

OBJECTIVE

This study was undertaken to gain insight on the cause of absent or reverse end-diastolic velocity (AREDV) in the umbilical artery (UA) of the donor twin by analysis of individual placental mass and vascular anastomoses in patients with twin-twin transfusion syndrome (TTTS) treated with laser.

STUDY DESIGN

TTTS patients who successfully underwent selective laser photocoagulation of communicating vessels (SLPCV), 16 and 26 weeks' gestation, with both twins born alive and complete Doppler and placental data were considered eligible for the study. Doppler examination of the UA was performed before and 24 hours after SLPCV. Abnormal UA Doppler findings were defined as persistent AREDV. Pre- and post-SLPCV UA Doppler results yielded the following 4 groups: (1) normal-normal; (2) normal-abnormal; (3) abnormal-normal; and (4) abnormal-abnormal. The types of vascular anastomoses were categorized during surgery. Individual placental territory (IPT) was defined as individual placental weight divided by total placental weight x 100.

RESULTS

There were 132 cases in group 1 and no patients in group 2. AREDV resolved in 78% (28/36) of patients (group 3) and remained unchanged in 22% (8/36) (group 4). The mean IPT-donor in group 4 was significantly smaller than in group 1 (P = .015). Patients with preoperative AREDV (groups 3 and 4) were more likely to have artery-to-artery anastomoses (P = .002). However, AREDV resolved in 57% (16/28) patients without artery-to-artery anastomoses.

CONCLUSION

Preoperative AREDV may result from a small IPT, placental vascular anastomoses, or both. AREDV resulting from a small IPT may have a similar cause to that of singletons, and may be inferred by lack of postoperative resolution. Resolution of AREDV after SLPCV implies the presence of an adequate IPT and removal of donor hypotension.

Recent findings on laser treatment of twin-to-twin transfusion syndrome

PURPOSE OF REVIEW

Despite the recent demonstration of the benefit of the primary laser over amnioreduction, overall survival is far from optimal (70-80%), and therefore diagnosis and management of early and late complications following placental surgery became of great importance.

RECENT FINDINGS

Laser therapy has proven to be better than amnioreduction in treating twin-to-twin transfusion syndrome. Miscarriage, preterm premature rupture of the membranes and preterm delivery account for more than 20% of perinatal mortality after treatment. In those who die despite treatment, recurrence of twin-to-twin transfusion syndrome, placental insufficiency or feto-fetal hemorrhage with anemia/polycythemia are complications that have to be managed with different secondary therapeutic options, such as amnioreduction, cord coagulation, intrauterine transfusion or repeat fetoscopy-guided laser. Ex-vivo placental angiography has confirmed that these complications occur when anastomoses are missed. Early predictors of laser efficacy in twin-to-twin transfusion syndrome treatment, such as improvement in the umbilical vein flow imbalance and urine production, are being evaluated, because they are earlier predictors of outcome than amniotic fluid discordance.

SUMMARY

Optimization of laser treatment of twin-to-twin transfusion syndrome and new insight into the follow-up are likely to become the key to a better prognosis, and they are therefore important issues that have to be addressed in forthcoming studies.

Sonographic umbilical cord morphometry and coiling patterns in twin–twin transfusion syndrome

OBJECTIVE

Monochorionic twins with twin-twin transfusion syndrome (TTTS) provide an ideal model in which to evaluate the influence of differing hemodynamic stress on umbilical cord (UC) morphology. The purpose of this study was to investigate the UC morphometry and UC coiling pattern at ultrasound in monochorionic twin pregnancies with TTTS.

METHODS

A targeted sonographic evaluation of the UC was performed in 21 consecutive twin pregnancies with untreated TTTS. The cross-sectional area of the UC and of its vessels was measured. The Wharton's jelly area was computed by subtracting the vessels area from the area of the UC. The umbilical coiling index (UCI) was calculated as the reciprocal of the sonographic length of one complete vascular coil. The UCs were classified as uncoiled, normally coiled, hypocoiled, hypercoiled and atypically coiled (UCI not valuable).

RESULTS

The UCs of recipient twins were invariably larger than those of donors, and this difference was mainly attributable to both a larger amount of Wharton's jelly and a larger umbilical vein diameter. The proportion of lean UCs was higher in the donor than in the recipient fetuses (18/21 vs 1/21, p < 0.0001), while large UCs were significantly more frequent in the recipient than in the donor twins (13/21 vs 1/21, p = 0.0002). In all twin pairs, a discordant umbilical coiling pattern was observed between the donor and the recipient twin. The prevalence of uncoiled and hypocoiled cords was higher in the donor group, while hypercoiling and atypical coiling were more frequently detected in the recipient group.

CONCLUSIONS

A discordant UC morphometry represents an additional phenotypic feature of twins with TTTS. The discordant intertwin coiling pattern in TTTS argues against an exclusively genetic origin of UC twists, and further supports a key role of hemodynamic forces in coiling development.