OC08.04: the Use of Aortic Displacement As a Surrogate for Intertwin Pulse Pressure Differences in Monochorionic Pregnancies with and Without TTTS

Twin–twin transfusion syndrome (TTTS) complicates 10–15% of monochorionic diamniotic (MCDA) twin pregnancies. It includes net transfer of blood and vasoactive mediators from donor to recipient causing increased recipient afterload and donor hypovolemia. No non-invasive technique is available to estimate fetal blood pressure. We hypothesise that aortic fractional area change (AFAC) reflects fetal pulse pressure. High frame rate four chamber views, including the transverse aorta, were collected prospectively in 56 MCDA twin pairs using a GE Voluson E8 with RAB6-D probe (GE Health Care, Austria). Four groups were studied: uncomplicated MCDA (n = 14); selective growth restriction (sIUGR, n = 5, weight discordance > 25%); TTTS stages 1 + 2 (n = 21) and TTTS stages 3 + 4 (n = 16). AFAC, defined as (max(area)-min(area))/max(area), was calculated off-line using dedicated speckle-tracking software (TomTec, Germany) averaged over 3 cardiac cycles with timing guided by anatomical M-mode. Intertwin-pair differences were calculated. Inter- and intraobserver reproducibility was tested using intercorrelation coefficient (ICC). Mean gestational age was 20.9 ± 3.1 weeks. Mean frame rate was 82 ± 29 Hz, with significantly higher donor frame rate (88 ± 34 vs. 82 ± 28, p = 0.035). Mean heart rates were similar at 142 ± 7 bpm. Inter- and intra-ICC were 0.986 and 0.957. Significant intertwin-pair differences were seen in both TTTS groups (table 1) consistent with higher pulse pressure in the recipient twin as compared to the donor co-twin. AFAC provides a quantifiable and reproducible method to assess aortic area change. This represents aortic distensibility, reflecting differences in intertwin-pair pulse pressure. Thus it is a promising tool to monitor changes after therapy.