Clinical significance of first trimester crown-rump length disparity in dichorionic twin gestations

OBJECTIVE: The purpose of this study was to determine the clinical significance of first trimester crown-rump disparity in dichorionic twin gestations. STUDY DESIGN: Ultrasound examinations of dichorionic twin pregnancies between 11 and 14 weeks of gestation were evaluated for growth discordance using crown-rump length. Medical records were reviewed for antenatal complications that included spontaneous abortion, fetal death, fetal structural or chromosomal anomalies, and preterm delivery. Fisher's exact test was used for statistical analysis; a probability value of <.05 was considered significant. RESULTS: Of 159 twin pregnancies, there were 7 fetal structural anomalies, 2 fetal chromosomal anomalies, 5 second-trimester spontaneous abortions, 3 second-trimester fetal deaths, and 1 third-trimester fetal death. Pregnancies that were complicated by fetal structural or chromosomal anomalies had significantly greater median crown-rump length discordance than pregnancies without fetal anomalies (4.0 mm vs 2.0 mm; P = .02). Crown-rump length discordance >10%, which is the 90th percentile for intertwin crown-rump length disparity in our population, was associated with a significantly higher incidence of fetal anomalies (22.2% vs 2.8%; P = .01). CONCLUSION: First trimester crown-rump length disparity in dichorionic twin gestations is associated with an increased risk of fetal structural and chromosomal anomalies.