P343: Longer latency of AEDF in monochorionic twins

Objective: To validate the clinical impression that absent enddiastolic flow (AEDF) in the umbilical artery (UA) in monochorionic (MC) has a longer latency compared to singleton or dichorionic (DC) twin pregnancies with AEDF. Methods: All patients with AEDF in the UA were identified by search of the patient databases in 2 fetal medicine centres. After excluding 21 pregnancies due to incomplete data (n = 18), and structural or chromosomal anomalies (n = 3), a total of 53 MC pregnancies were compared with two cohort groups – singleton pregnancies (n = 74) and dichorionic twins (n = 19). Latency was defined as days from diagnosis of AEDF till delivery or intrauterine death. Results: A total of 146 pregnancies with AEDF were analysed, including 25 MC twins with IUGR (17%) and 28 with TTTS (19%). Median latency was 43 days (7–153) in the MC group, 30 days (1–66) in the DC group and 10 days (range 0–68) in the singletons. MC twins had significantly longer latency than the singletons (p = 0.007), but there was no significant difference with the DCDA. After excluding the TTTS group, non-TTTS MC twins had a significantly longer latency than DC twins. The overall median gestational age at onset of AEDF [176 days (range: 108–253)] was significantly earlier in MC twins (median 147 days) than in DC (190 days) or singleton (189.50 days) pregnancies (p < 0.001). Latency was linearly correlated with gestational age at onset of AEDF (R2 = 0.564). Conclusion: The latency of AEDF is longer in MC twins, suggesting a different patho-physiological mechanism then simple downstream resistance.