OC112: The natural history of monochorionic twins and the role of prenatal ultrasound scan

Abstract

To examine the outcome in a prospective series of monochorionic diamniotic twins included in the first trimester and to evaluate the role of first- and early second-trimester scan in predicting a complicated outcome, defined as the development of TTTS, severe discordant growth or single/double demise. Patients were scanned in the first trimester, at 16, 20 and 26 weeks. Information on pregnancy and neonatal outcome was provided by the referring physician. Of the 194 included twin pregnancies, 165 (85%) resulted in the survival of both, 14 (7.5%) in the survival of one and 15 (7.5%) ended with no survivors. Total loss rate was 43/388 (11%), most occurring at ⩽ 24 weeks (36/43; 84%). In ongoing twin pregnancies > 32 weeks, the prospective risk of IUFD was 1/150 (0.69%; 95% CI, 0.03–3.2). TTTS occurred in 17/194 (8.8%). Overall survival of treated cases was 67% (16/24) and survival of at least one was 80% (12/15). TTTS accounted for 18/43 (42%) of all losses, but discordant growth for only three. Discordant anomalies were present in 15/388 (3.8%). Severe hemoglobin discordances at birth occurred in 7/167 (4.2%) liveborn pairs, requiring immediate transfusion and/or partial exchange transfusion. Predictors of complicated outcome were Δ crown–rump length (CRL) in the first trimester (OR 8.45; P = 0.0094), together with Δ abdominal circumference (AC) (OR 37.62; P = 0.0002) and concordant amniotic fluid (OR 0.19; P = 0.0030) at 16 weeks. The formula to predict outcome was calculated as Y = − 1.8004 + (0.1423 × Δ CRL) + (0.1170 × ΔAC)− (0.8229 × amniotic fluid), where the probability for complicated outcome is 1/(1 + exp(−Y)). With ‘> 50% chance of complicated outcome’ as cut-off, the sensitivity was 52% with a PPV of 75%. The survival rate was 89%, with most losses at ⩽ 24 weeks. TTTS occurred in 8.8%, whereas 4.2% had severe hemoglobin discordances at birth. Combined first- and early second-trimester scan identified 52% of cases with a complicated outcome.