Chorionic bump on first-trimester sonography: not necessarily a poor prognostic indicator for pregnancy

The purpose of this study was to determine the live birth rate of pregnancies with a diagnosis of a chorionic bump, a convex bulge from the choriodecidual surface into the first-trimester gestational sac.

Pregnant patients at least 18 years old with the finding of a chorionic bump on first-trimester sonography were included in this prospective observational study. The independent variables were chorionic bump size and number and presence or absence of a history of infertility or coagulation disorder. The primary end point was pregnancy outcome.

During the 4-year study period, 52 pregnancies had a diagnosis of a chorionic bump. Overall, 34 resulted in live births, corresponding to an absolute live birth rate of 65%, and 18 were nonviable. Forty-one chorionic bump pregnancies were otherwise normal (ie, pregnancies in which a gestational sac, yolk sac, and embryo with heartbeat were seen at some point), and in this subset, the live birth rate was 83% (34 of 41). All pregnancies with more than 1 chorionic bump (4) ended in demise (100%). The average maximum dimension of the chorionic bump was 1.3 cm (range, 0.5-3.8 cm); however there was not a statistically significant correlation between chorionic bump size and pregnancy outcome (P = .5866; odds ratio, 0.54; 95% confidence interval, 0.06-5.01). Nine patients (17%) had a history of infertility treatment, and 4 (8%) had a history of coagulation disorder. Only 1 chorionic bump pregnancy was associated with a birth defect.

The live birth rate in our chorionic bump cohort was 65% overall and even higher (83%) if the pregnancy was otherwise normal. The clinical implication is that a chorionic bump on first-trimester sonography is not necessarily associated with a guarded prognosis.