First trimester intervention in twin reversed arterial perfusion (TRAP) sequence – does size matter?

Objective: To evaluate the outcome of first trimester intervention (12⁺⁰ to 13⁺⁶ weeks of gestation) in pregnancies complicated by TRAP sequence.

Methods: From 2010 onwards, all patients diagnosed with monochorionic diamniotic TRAP sequence undergoing intrafetal laser ablation (IFL) prior to 14⁺⁰ weeks of gestation at the University of Bonn were retrospectively analysed for intrauterine course and pregnancy outcome.

Results: In the study period twelve patients were treated by IFL. The mean gestational age at intervention was 13.1 ± 0.5 weeks (range 12⁺⁴ – 13⁺⁶). In all cases one intervention sufficed to disrupt the perfusion of the TRAP twin. No case of abortion, preterm premature rupture of membranes (PPROM) or haemorrhage occurred.

In five pregnancies (41.7%) daily follow up scans demonstrated intrauterine death of the pump twin at a mean of 67.2 ± 20.0 hours (range 48 – 96) after intervention. The remaining 7 pregnancies continued uneventfully with birth of a healthy infant at term.

A comparison of survivors and non-survivors identified a significant difference in the median discordance between the crown-rump length (CRL) of the pump twin and the upper pole-rump length (URL) of the TRAP twin (0.56 vs. 0.36; p < 0.05). A CRL-URL/CRL ratio > 0.48 identified all 7 survivors (p < 0.05). All other assessed parameters were not significantly different.

Conclusion: Although technically feasible, IFL in TRAP sequence performed in the first trimester has a significant fetal loss rate. A large TRAP twins size and a small pump twins size seems to be associated with an unfavourable outcome of IFL.