First-trimester chorionic bump--Association with fetal aneuploidy in a high-risk population.

PURPOSE: To determine the relationship between the first-trimester chorionic bump and fetal aneuploidy.

METHODS: This retrospective cohort study included all singleton pregnancies with chromosomal analysis and sonographic examination performed between 5 0/7 and 13 6/7 weeks from January 1, 2010 through August 15, 2015. Interobserver and intraobserver agreement for identifying a chorionic bump was evaluated by the Kappa statistic. Pregnancies with and without a chorionic bump were compared regarding patient characteristics and fetal karyotypes.

RESULTS: Six hundred ninety subjects were included, 16 (2.3%) having a bump. The kappa coefficients for interobserver agreement were 0.88 (95% confidence interval [CI]: 0.71-1.00) and 0.94 (95% CI: 0.82-1.00); those for intraobserver agreement were 0.81 (95% CI: 0.61-1.00) and perfect agreement. One hundred seventeen fetuses (16.9%) were aneuploid, of which five (4.3%) had a bump. The odds of aneuploidy in the presence of a chorionic bump were higher than those in the absence of a chorionic bump, although this difference was not statistically significant (odds ratio [OR] 2.3, 95% CI: 0.8-6.7). In subgroup analyses, odds of aneuploidy were four times higher in the bump group than in the no bump group among those with a sonographically isolated bump (OR 4.5, 95% CI: 1.5-13.5) and 15 times higher among those with an isolated bump and increased first-trimester aneuploidy risk (OR 15.0, 95% CI 2.4-93.3).

CONCLUSIONS: Agreement in identifying chorionic bumps is near-perfect. A sonographically nonisolated chorionic bump is not associated with significant additional aneuploidy risk, whereas a sonographically isolated chorionic bump confers a significantly increased likelihood of aneuploidy in high-risk fetuses. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:3-7, 2017.