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284: First trimester risk assessment and adverse outcomes in monochorionic twin pregnancies

      Objective

      High rates of adverse outcomes in MCDA twin pregnancies are related to the twin-twin transfusion syndrome (TTTS) and abnormal fetal growth. Our objective was to identify first-trimester factors associated with these outcomes.

      Study Design

      All MCDA pregnancies managed between 2003 and 2007 that had first trimester aneuploidy risk assessments were reviewed. Discordance in birthweights (BW) and crown-rump lengths (CRLs) was the difference in measurements divided by the larger value. Delivery information was extracted from electronic medical records. Statistical analysis was performed with Spearman rho correlation, Fisher′s exact test, and Mann-Whitney U.

      Results

      Six five pregnancies met inclusion criteria. There were six cases of TTTS, and three second trimester IUFDs. Delivery information was available in 47 cases. There was no correlation between CRLs, NTs, or biochemical values and the subsequent diagnosis of TTTS. BW discordance of >20% was noted in 24.5% of pregnancies, and IUGR was noted in at least one neonate in 53% of pregnancies. CRL discordance was strongly correlated with BW discordance (rho=.41; p=.004). Those pregnancies with IUGR had higher degrees of CRL discordance than pregnancies without IUGR (4.9% vs. 1.4%; p=.02). NT discordance was not associated with BW discordance or IUGR. NT values >95th%ile were also not associated with higher rates of BW discordance or IUGR. There was no correlation between levels of PAPP-A or free beta-hCG and growth discordance or IUGR.

      Conclusion

      At 11-14 weeks, the degree of CRL discordance correlates with BW discordance as well as IUGR in MCDA pregnancies. Neither NT nor biochemical values predict growth abnormalities. Because a strong association between low PAPP-A and abnormal growth has been demonstrated in singleton pregnancies, mechanisms other than placental insufficiency likely affect monochorionic twin pregnancies with IUGR or discordant growth.