Objective
The aim of this study was to document the mortality of twin reversed arterial perfusion (TRAP) sequence from the first trimester to planned intervention at 16-18 weeks.
Study Design
A retrospective review was performed of the outcome of monochorionic twin pregnancies diagnosed with twin reversed arterial perfusion sequence in the first trimester.
Results
Twenty-six pregnancies were diagnosed with twin reversed arterial perfusion sequence in the first trimester: 2 opted for termination of pregnancy and 24 opted for prophylactic intervention to arrest the reversed flow, which was planned at 16-18 weeks. In 8 of 24 (33%) pregnancies, spontaneous death of the pump twin occurred between diagnosis and planned intervention. In 5 of 24 (21%), there was a spontaneous arrest of flow; whereas, in 11 (46%) there was persistent flow toward the acardiac twin at 16-18 weeks.
Conclusion
Twin reversed arterial perfusion carries a high mortality between the first and early second trimester.
Twin reversed arterial perfusion (TRAP) sequence is an abnormality unique to monochorionic twins with an estimated prevalence of approximately 1 in 35,000 pregnancies. In TRAP, the acardiac twin is a true parasite receiving blood from the pump twin through an arterioarterial anastomosis. The condition is associated with a high risk of perinatal death of the pump twin caused by a combination of high-output cardiac failure and polyhydramnios-related preterm birth. The outcome may be improved by intrauterine intervention to arrest the circulation of the acardiac twin. Traditionally, these procedures are carried out in the second trimester because the condition was usually first diagnosed at the routine anomaly scan.
More recently, TRAP is increasingly being diagnosed in the first trimester as a consequence of the widespread introduction of the 11 + 0 to 13 + 6 weeks’ scan for measurement of nuchal translucency in the screening for chromosomal abnormalities. Despite earlier diagnosis, intrauterine interventions have been reserved for after 16 weeks because the experience with early amniocentesis suggested that the risk of miscarriage and the development of severe talipes are substantially increased with such interventions before obliteration of the celomic cavity. The aim of this study is to report the natural history of TRAP sequence from diagnosis between 11 + 0 and 13 + 6 weeks’ gestation to planned intervention at 16-18 weeks.
Materials and Methods
We retrospectively reviewed the outcome of all monochorionic twin pregnancies diagnosed with TRAP sequence in the first trimester in 2 tertiary referral centers (January 1999 to December 2008 in King’s College Hospital in London and January 2006 to January 2009 in the University Hospitals in Leuven). TRAP sequence was diagnosed in a monochorionic pregnancy by the coexistence of a normal fetus and an abnormal twin without functional cardiac activity and with reversed arterial flow in the umbilical artery as demonstrated by color Doppler. In each case, a detailed scan was carried out for the diagnosis of any major defects in the pump twin and measurement of fetal crown-rump length and nuchal translucency thickness. We also measured the longitudinal distance between upper pole and rump of the acardiac fetus. Cases that underwent a termination of pregnancy in the first trimester were excluded from the analysis.
All patients were counseled about the condition and the different options, including termination of the entire pregnancy, expectant management with intervention to arrest the reversed perfusion only if signs of fetal compromise develop or prophylactic intervention after 16 weeks. Patients who opted for a prophylactic intervention were given an appointment at the treatment center at 16-18 weeks of gestation. Most also had an additional ultrasound scan in the meantime to assess fetal viability and the blood flow in the acardiac twin either at the treatment centre or at the referring institution. The technique used to arrest the flow toward the acardiac twin consisted of either ultrasound-guided intrafetal coagulation or fetoscopic laser coagulation of the umbilical cord and/or placental anastomoses. Intrafetal coagulation was performed by using a laser fiber (Dornier MedTech Europe, Wessling, Germany) through an 18 G needle (Cook Medical, Limmerick, Ireland) or by a 17 G radiofrequency needle (Cooltip RF ablation system; Valleylab, Boulder, CO). Fetoscopic laser coagulation was performed with a 2.3- or 1.0-mm endoscope housed in a sheath with an operative channel (Karl Storz, Tuttlingen, Germany) for the laser fiber (Dornier Medtech Europe).
Differences between continuous variables were analyzed by Mann-Whitney U test at significance levels of P < .05.
Results
The diagnosis of TRAP sequence was made between 11 + 0 and 13 + 6 weeks of gestation in 26 monochorionic twin pregnancies (23 diamniotic and 3 monoamniotic). There were 2 terminations in the first trimester: one on parental request and the other after the diagnosis of skeletal and brain abnormalities in the pump twin. These 2 pregnancies were excluded from the analysis. The demographic and clinical details of the 24 continuing pregnancies are summarized in the Table .
| Variable | n |
|---|---|
| Demographic details | |
| Maternal age, y | 29 ± 6 |
| Nulliparous women | 15/24 (62%) |
| Spontaneous conceptions | 22/24 (92%) |
| White | 20/24 (83%) |
| Clinical details at first presentation | |
| GA at first presentation, wk | 12.3 ± 0.6 |
| CRL pump, mm | 62 ± 8 |
| URL acardiac, mm | 36 ± 12 |
| CRL pump-URL acadiac/CRL pump | 0.43 ± 0.16 |
| NT pump above the 95th percentile | 1/24 (4%) |
| Clinical details of pregnancy outcome | |
| Overall survival rate | 11/24 (46%) |
| TOP for defects in pump twin | 2/24 (8%) |
| Spontaneous demise pump twin | 9/24 (38%) a |
| Miscarriage | 2/24 (8%) |
| Birthweight of liveborn pump twin, g | 2465 ± 751 |
| GA of liveborn pump twin, wk | 36 ± 4 |
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