Review of the correlation between blood flow velocity and polycythemia in the fetus, neonate and adult: appropriate diagnostic levels need to be determined for twin anemia-polycythemia sequence

Twin Anemia-Polycythemia Sequence (TAPS): From Basic Research to Clinical Practice

Twin pregnancy is associated with an increased risk of perinatal and maternal complications, and early establishment of the chorionicity type defines this risk. In monochorionic (MC) pregnancies, the fetuses share the same placental mass and exhibit vascular anastomoses crossing the intertwin membrane, and the combination and pattern of anastomoses determine the primary clinical picture and occurrence of future complications. Twin Anemia-Polycythemia Sequence (TAPS) was first described in 2006 after fetoscopic laser surgery in twin-to-twin transfusion syndrome (TTTS) twins, and in 2007, the first spontaneous cases were reported, recognizing TAPS as an individualized vascular identity in fetofetal transfusion syndromes. There are two types of TAPS: spontaneous (3-5%) and iatrogenic or postlaser (2-16%). TAPS consists of small diameter arteriovenous anastomoses (<1 mm) and low-rate, small-caliber AA anastomoses in the absence of amniotic fluid discordances. There are certain antenatal and postnatal diagnostic criteria, which have progressively evolved over time. New, additional secondary markers have been proposed, and their reliability is being studied. The best screening protocol for TAPS in MC twins is still a matter of debate. This review provides a survey of the relevant literature on the epidemiology, vascular pathophysiology, underlying hemodynamic factors that regulate mismatched vascular connections, and diagnostic criteria of this condition. The aim is to increase awareness and knowledge about this recently identified and frequently unrecognized and misdiagnosed pathology.

Pathophysiology, diagnosis, and management of twin anemia polycythemia sequence in monochorionic multiple gestations

Twin anemia polycythemia sequence (TAPS) is a consequence of unequal sharing of red blood cells between monochorionic twins resulting in anemia in the donor and polycythemia in the recipient twin. Prenatally TAPS can occur spontaneously or complicate incomplete laser surgery for twin transfusion syndrome. While there may be clinical overlap with twin transfusion syndrome or selective fetal growth restriction, diagnosis relies on Doppler measurement of middle cerebral artery peak systolic velocities. Significantly discordant velocities are diagnostic, while severity staging is based on signs of cardiovascular compromise. Conservative management, fetoscopic laser coagulation, selective twin reduction, fetal blood and exchange transfusion, and delivery may be selected guided by the gestational age of diagnosis, the severity of the condition, the likelihood of success, and the patients' priorities. Prenatal curative treatment that minimizes the risk for prematurity and residual morbidity at birth is most likely to offer the greatest short-term and long-term benefits.

Twin to twin transfusion syndrome

Twin to twin transfusion syndrome (TTTS) is a common complication that typically presents in the second trimester of pregnancy in 10-15% of monochorionic twins due to net transfer of volume and hormonal substances from one twin to the other across vascular anastomoses on the placenta. Without recognition and treatment, TTTS is the greatest contributor to fetal loss prior to viability in 90-100% of advanced cases. Ultrasound diagnosis of monochorionicity is most reliable in the first trimester and sets the monitoring strategy for this type of twins. The diagnosis of TTTS is made by ultrasound with the findings of polyhydramnios due to volume overload and polyuria in one twin and oligohydramnios due to oliguria of the co-twin. Assessment of bladder filling as well as arterial and venous Doppler patterns are required for staging disease severity. Assessment of fetal cardiac function also provides additional insight into the fetal cardiovascular impacts of the disease as well as help identify fetuses that may require postnatal follow up. Fetoscopic laser ablation of the communicating vascular anastomoses between the twins is the standard treatment for TTTS. It aims to cure the condition by interrupting the link between their circulations and making them independent of one another. Contemporary outcome data after laser surgery suggests survival for both fetuses can be anticipated in up to 65% of cases and survival of a single fetus in up to 88% of cases. However, preterm birth remains a significant contributor to postnatal morbidity and mortality. Long term outcomes of TTTS survivors indicate that up to 11% of children may show signs of neurologic impairment. Strategies to minimize preterm birth after treatment and standardized reporting by laser centers are important considerations to improve overall outcomes and understand the long-term impacts of TTTS.

Middle Cerebral Artery Doppler Velocimetry for the Diagnosis of Twin Anemia Polycythemia Sequence: A Systematic Review

Twin anemia polycythemia sequence (TAPS) is a rare complication of monochorionic diamniotic (MCDA) twins. Middle cerebral artery peak systolic velocity (MCA-PSV) measurements are used to screen for TAPS while fetal or neonatal hemoglobin levels are required for definitive diagnosis. We sought to perform a systematic review of the efficacy of MCA-PSV in diagnosing TAPS. Search criteria were developed using relevant terms to query the Pubmed, Embase, and SCOPUS electronic databases. Publications reporting diagnostic characteristics of MCA-PSV measurements (i.e., sensitivity, specificity or receiver operator curves) were included. Each article was assessed for bias using the Quality Assessment of Diagnostic Accuracy Studies II (QUADAS II) tool. Results were assessed for uniformity to determine whether meta-analysis was feasible. Data were presented in tabular form. Among publications, five met the inclusion criteria. QUADAS II analysis revealed that four of the publications were highly likely to have bias in multiple areas. Meta-analysis was precluded by non-uniformity between definitions of TAPS by MCA-PSV and neonatal or fetal hemoglobin levels. High-quality prospective studies with consistent definitions and ultrasound surveillance protocols are still required to determine the efficacy of MCA-PSV in diagnosing TAPS. Other ultrasound findings (e.g., placenta echogenicity discordance) may augment Doppler studies.

Intrauterine Interventions for the Treatment of Twin Anemia-Polycythemia Sequence: A Systematic Review

BACKGROUND

Twin anemia-polycythemia sequence (TAPS) is a complication of monochorionic, multiple gestation pregnancies in which blood shunting through placental anastomoses results in chronic anemia in one fetus and chronic polycythemia in another. The outcomes of different treatment modalities for TAPS are not well known.

OBJECTIVE

To determine the outcomes of the intrauterine interventions used to treat TAPS.

STUDY DESIGN

A systematic literature search of MEDLINE, EMBASE, and CENTRAL was performed in June 2016. Primary outcomes were mortality, morbidity, and adverse perinatal outcomes. Data were summarized in the form of weighted means, and statistical difference was determined.

RESULTS

Twenty-one articles were identified for inclusion in this review and were composed of 105 cases of TAPS. In the cases presented in the literature, there was no statistically significant difference in mortality, morbidity, or emergent Caesarean section rates between expectant management, intrauterine transfusion (IUT), and laser ablation therapy. Laser ablation therapy and IUT were found to have a significantly lower rate of adverse perinatal outcomes when compared to expectantly managed cases.

CONCLUSIONS

The literature looking into the treatment of TAPS is very limited, with no randomized controlled trials and only one includable comparative study. Based on the data in the case report and case study literature, there is no mortality difference between any of the treatment modalities. Expectant management may be associated with an increase in adverse perinatal outcomes when compared to laser therapy and IUT. More comparative studies are needed to assist clinicians in adopting an evidence-based approach to the treatment of TAPS.

Relationship between fetal peak systolic velocity in Middle cerebral artery and umbilical blood gas values and hemoglobin levels in diabetic pregnant women

PURPOSE

To assess the relationship between peak systolic velocity in the middle cerebral artery (MCA-PSV) and fetal hypoxia in diabetic pregnant women requiring insulin therapy.

METHODS

The data of diabetic pregnant women using insulin who were followed in our departments were reviewed retrospectively. The relationships between MCA-PSV and umbilical cord pO2, pCO2, base deficit, hemoglobin, and birth weight were analyzed.

RESULTS

A total of 120 cases were included in the final analysis. The median (Q₁ - Q₃ ) gestational age at Doppler evaluation was 37 weeks 3 days (37-38 weeks and 2 days), and the mean ± SD gestational age at delivery was 38 weeks 4 days ± 3days. The mean ± SD hemoglobin A1c (HbA1c) level was 5.7% ± 1.0% and, median (Q₁ -Q₃ ) daily total insulin dose was 25 U (10U-48U). There was no statistically significant correlation between MCA-PSV and pH, PO2, PCO2, base deficit, Hb, and birth weight (Spearman correlation, r:-.001[P = .99], r:-.011[P = .90], r:-.052 [P = .51], r: .049[P = .59], r: .049 [P = .59], r: .030 [P = .75], respectively). Using binary logistic regression analysis, no independent factor for the prediction of fetal acidosis (venous pH < 7.23), and metabolic acidosis (base deficit >6.3 mmol/L) was detected.

CONCLUSION

MCA-PSV is not a good indicator of fetal polycythemia or chronic hypoxia in fetuses of diabetic pregnant women. Fetal well-being should be monitored with other tools in these circumstances.

Can middle cerebral artery peak systolic velocity predict polycythemia in monochorionic-diamniotic twins? Evidence from a prospective cohort study

OBJECTIVE

The antenatal diagnosis of twin anemia-polycythemia sequence (TAPS) in monochorionic-diamniotic (MCDA) twin pregnancies is based on elevated peak systolic velocity in the middle cerebral artery (MCA-PSV) in the donor twin and decreased MCA-PSV in the recipient twin. However, the association between these parameters and polycythemia has not yet been established. The aim of this study was to determine whether MCA-PSV can predict polycythemia in MCDA pregnancies.

METHODS

This was a prospective cohort study of MCDA pregnancies recruited at 14-18 weeks' gestation from a single tertiary care center between January 2011 and June 2014. Fetal MCA Doppler waveforms were recorded every 2 weeks from 18 weeks' gestation until delivery. Only those with an MCA-PSV measurement within 1 week of delivery were included in the analysis. Neonatal hematocrit level was determined in all twins from venous blood obtained within 4 h of delivery. Polycythemia was defined as a hematocrit of > 65%, and anemia as a hematocrit of < 45%. TAPS was diagnosed when an intertwin hemoglobin difference of > 8 g/dL and reticulocyte count ratio of > 1.7 were observed.

RESULTS

Of 162 MCDA pregnancies followed during the study period, 69 had an MCA-PSV measurement within 1 week of delivery and were included in the study. Twenty-five neonates were diagnosed with polycythemia and nine twin pairs met the criteria for TAPS. In a pooled analysis, MCA-PSV was negatively correlated with neonatal hematocrit (P = 0.017, r = -0.215) and was significantly higher in anemic fetuses than in normal controls (1.15 multiples of the median (MoM) vs 1.02 MoM, respectively; P = 0.001). However, MCA-PSV was similar among polycythemic and normal fetuses (0.95 MoM vs 1.02 MoM, respectively; P = 0.47). Intertwin difference in MCA-PSV (delta MCA-PSV) was positively correlated with intertwin hematocrit difference (P = 0.002, r = 0.394). Moreover, twin pregnancies with an intertwin hematocrit difference of > 24% had a significantly greater delta MCA-PSV than did those with an intertwin hematocrit difference of ≤ 24% (delta MCA-PSV, 19 vs 5 cm/s; P < 0.001).

CONCLUSIONS

MCA-PSV is not significantly decreased in polycythemic MCDA twins. However, delta MCA-PSV is associated with a large intertwin difference in hematocrit, and its use may be better than conventional methods for the risk assessment of TAPS. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Uncommon complications of monochorionic twin pregnancies: Twin anaemia-polycythaemia sequence

Introduction

Twin anaemia-polycythaemia sequence (TAPS) occurs when significant haemoglobin discordance exists between monochorionic fetuses. Most reported cases occur iatrogenically after twin-to-twin transfusion syndrome (TTTS) laser therapy; spontaneous TAPS is also reported. The purpose of this study was to investigate pregnancy management and immediate neonatal outcomes for monochorionic multiple pregnancies complicated by TAPS referred to the NSW Fetal Therapy Centre (FTC).

Methods

Retrospective cohort study of multiple pregnancies referred to NSW FTC between April 2006 and April 2014. Fourteen TAPS cases [discordant middle cerebral artery peak systolic volume (MCA-PSV) or clinician diagnosis antenatally, or Hb >20 g/dL vs. <12 g/dL post-natally] were compared to an existing TTTS database (n = 142) and uncomplicated monochorionic diamniotic (MCDA) twin pregnancies (n = 45). Outcomes measured were maternal demographics; ultrasound findings at referral; management, including whether in utero fetal therapy was performed; and pregnancy outcome, including gestation at birth, mode of birth, birthweight, fetal/neonatal complications and neonatal survival to discharge.

Results

The majority of TAPS cases were spontaneous (9/14) and occurred later in pregnancy than TTTS (median gestation at diagnosis 26.0 ± 4.9 vs. 20.4 ± 2.6 weeks, P < 0.001). However, TAPS perinatal outcome was similar to TTTS (survival of both twins 62% vs. 53%, survival of at least one twin 85% vs. 87%, overall survival 73% vs. 70%) and overall survival significantly lower than for uncomplicated MCDA pregnancies (73% vs. 98%, P < 0.001).

Conclusion

Overall mortality for TAPS was similar to that of TTTS but significantly higher compared to uncomplicated MCDA pregnancies, underscoring the potential severity of TAPS despite its later gestational onset.