Abnormal number of fetal ribs on 3-dimensional ultrasonography: associated anomalies and outcomes in 75 fetuses.

Objective: The purpose of this study was to describe the clinical importance of an abnormal number of fetal ribs.

Methods: A retrospective study of all fetuses that were found to have an abnormal number of ribs during routine ultrasonographic examinations was performed. Volume data sets of the fetal ribs were acquired by either static 3- or 4-dimensional volume contrast imaging in plane C. In all cases, a meticulous survey of the fetal anatomy was performed, and prenatal and postnatal records were reviewed.

Results: Seventy-five fetuses were found retrospectively to have an abnormal number of ribs. Ultrasonographic examinations were done between 14 and 31 weeks' gestation (mean, 21.8 weeks; median, 23 weeks). More than 24 ribs were found in 28 fetuses (37%), and fewer than 24 ribs were found in 47 (63%). Additional anomalies were found in 22 fetuses (29%). Cardiovascular anomalies were detected in 10 fetuses. Seven fetuses had renal anomalies. Two fetuses had mild ventriculomegaly, and 1 fetus had holoprosencephaly. Lung dysplasia was found in 2 cases. One fetus had enlarged nuchal translucency with wormian bones. Termination of pregnancy was performed in 3 cases because of major malformations. The other 19 fetuses with associated abnormalities and the 53 without associated anomalies were born alive with only minor anomalies.

Conclusions: An abnormal number of fetal ribs is an isolated finding in most cases. It may also be seen with major anomalies; however, more frequently the anomalies are minor, and the overall prognosis is good.