A screening interval greater than 14 days was associated with a late Quintero stage at diagnosis with an odds ration (OR) of 9.45 (95% confidence interval [CI] 1.8–50.4). When controlled for gestational age at diagnosis, a longer screening interval was still associated with a later Quintero stage with an adjusted OR of 9.8 (95% CI 1.8–52.9).
Our study suggests that a shorter surveillance interval in monochorionic-diamniotic gestations results in an earlier stage of twin–twin transfusion syndrome at diagnosis. These data support the findings from Sueters et al that twin–twin transfusion syndrome is diagnosed at an earlier stage when ultrasound surveillance is every 2 weeks combined with symptoms of hydramnios.12 Earlier stage at diagnosis has been shown in previous studies to be an important prognostic factor in successful pregnancy outcome.11,13 It is also well documented that perinatal survival decreases with increasing twin–twin transfusion syndrome stage.5,14–16 For example, the rate of survival in the Eurofetus trial for at least one twin was higher in pregnancies diagnosed at stage I or II (53 of 73 [73%]) compared with those diagnosed at stages III or IV (38 of 69 [55%]).11
The median gestational age for diagnosis of twin–twin transfusion syndrome in our series was 19 6/7 weeks, with a range of 15 3/7–36 3/7 weeks and a peak incidence of 18 0/7–18 6/7 weeks. Although two-thirds of the cases were diagnosed between 15 and 22 weeks, the other third were diagnosed between 22 and 36 weeks. This suggests that screening should begin before 18 weeks in known monochorionic-diamniotic gestations and screening should continue throughout the pregnancy until delivery. Given our findings of twin–twin transfusion syndrome diagnosed in the early second trimester and late third trimester, we recommend initiation of screening by 16 weeks and continuing ultrasound surveillance every 2 weeks until delivery. This is consistent with the RCOG and the CNGOF, which recommend ultrasound examinations at least twice a month for monochorionic-diamniotic pregnancies.6,7 Approximately half (53%) of the cases in our series were diagnosed with twin–twin transfusion syndrome at the time of fetal anatomic survey. More than half (24 of 42) of the cases of twin–twin transfusion syndrome had a previous ultrasonogram documenting a monochorionic-diamniotic gestation, yet the interval between ultrasonograms varied markedly from 3 to 63 days. Given what we know about the increased incidence of complications of monochorionic gestations, it is important to not only definitively diagnose monochorionic twin gestations (ie, not simply as “twins”) but to institute an earlier and more intensive screening strategy than in diamniotic gestations.17,18 Earlier detection of twin–twin transfusion syndrome by more frequent ultrasound screening may result in improved outcomes for the condition, as fewer pregnancies will be diagnosed in late stages.
Another advantage to earlier detection of twin–twin transfusion syndrome is the ability to effectively counsel patients regarding available management options (expectant management, delivery, termination, selective feticide, septostomy, amnioreduction, laser photocoagulation) and to initiate timely transfer to a treatment center if electing to proceed with intervention. More frequent surveillance of monochorionic pregnancies may allow for earlier detection of other complications of monochorionic gestations such as discordant anomalies, discordant uteroplacental insufficiency, and twin-reversed arterial perfusion sequence.
The objective of any screening strategy is to detect a disease in its early stages, thereby allowing for more timely intervention and, it is hoped, better outcomes. One requirement of a screening strategy is that effective treatment is available for the condition being screened. Given what we currently know about twin–twin transfusion syndrome, this criterion is met in that laser photocoagulation of communicating vessels effectively treats the condition in the majority of patients.11 If detected and managed in its early stages, the diagnosis of twin–twin transfusion syndrome need not be as grim as it has been in the past.
The Maternal-Fetal Medicine division at our institution has adopted a similar strategy to what is recommended in Europe.6,7 Every effort is made to accurately diagnose chorionicity at the first ultrasound examination. We initiate surveillance of known monochorionic gestations no later than 16 weeks and evaluate monochorionic pregnancies every 2 weeks for evidence of twin–twin transfusion syndrome and other complications of monochorionic gestations. Amniotic fluid volume and bladder status are evaluated on each ultrasonogram. Doppler evaluation is preformed only if an abnormality is identified. Growth is measured every 4 weeks. In cases in which findings have raised the suspicion for development of twin–twin transfusion syndrome, patients have increased frequency of ultrasound examinations.
Magee-Womens Hospital is a tertiary care center that serves as an ultrasound referral center for Western Pennsylvania, West Virginia, and Eastern Ohio. Previous ultrasound data were not available on 18 of 42 patients. Judging by the indications for the examinations, these patients were either referred for their anatomic survey or urgently referred because of an abnormal ultrasonogram in the community (suspected twin–twin transfusion syndrome, suspected monoamniotic twins, increased risk for open neural tube defect). When evaluating only the 24 pregnancies with a previous ultrasonogram, our results still indicate that the twin–twin transfusion syndrome is more likely to be detected at a later stage when the ultrasound interval is greater than 14 days (P=.028). This series represents a mix of patients managed by both academic and community ob-gyns. Many referring physicians did not distinguish monochorionic from dichorionic twin gestations, which may explain why half of the cases in our series had “anatomic survey” listed as the indication for the ultrasonogram that diagnosed twin–twin transfusion syndrome, even when monochorionic status was known.
An obvious disadvantage of our study is the retrospective design, which may allow for the introduction of various biases, such as selection and sampling bias. Given the relatively small number of cases, we had to dichotomize variables of interest to short compared with long screening interval and early compared with late stages. The ultrasound screening interval of 14 days or less or greater than 14 days was predetermined based on our current practice. A larger sample size would have allowed for a more thorough analysis of time intervals such as 1 week, 2 weeks, 3 weeks, 4 weeks, and greater than 4 weeks. Nonetheless, only two patients in the 14-days-or-less interval group were diagnosed with late-stage twin–twin transfusion syndrome. A prospective, multicenter cohort of monochorionic-diamniotic gestations would best describe the natural history of these multiple gestations.
In a recent review in the American Journal of Obstetrics and Gynecology, Stamilio and colleagues argue that “… there is normative equipoise to justify the performance of randomized clinical trials to identify the optimal treatment strategy for mild [twin–twin transfusion syndrome].”19 This will require identifying twin–twin transfusion syndrome in the early stages, which occurred in only 57% (24 of 42) of cases in our series.
We encourage obstetric care providers to be more cognizant of the need to treat monochorionic gestations differently than dichorionic gestations, and to recognize that the ultrasound diagnosis of simply “twins” is insufficient. Finally, we hope that our study aids in the development of evidence-based recommendations for sonographic surveillance of monochorionic gestations.
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© 2011 The American College of Obstetricians and Gynecologists
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