Prenatal diagnosis of isolated abnormal number of ribs.
OBJECTIVE
To determine the incidence of prenatal isolated abnormal number of ribs, using three-dimensional (3D) ultrasound.


METHODS
This was a prospective study of low-risk women with singleton pregnancy and normal fetal anatomy scan. 3D examinations of the fetal ribs were carried out at the time of the routine anomaly scan at 14-16 or 20-24 weeks of gestation. A 3D volume of the spine was acquired with a mechanical sweep that lasted between 2 and 4 s per volume and was performed when the fetus had a minimally flexed head position. Fetal ribs were reviewed on the rendered image (maximal mode), both while the patient was in the clinic and again later.


RESULTS
Three hundred and sixty-seven pregnant women were evaluated. Twenty-three (6.3%) fetuses were found to have an abnormal number of ribs. Fifteen (4.1%) had 11 ribs unilaterally, with the last (12(th)) rib missing. One patient (0.27%) had 13 ribs unilaterally (with a small extra rib after the last rib). Two (0.5%) patients had 13 ribs bilaterally with an extra rib after the 12(th) rib on each side and two (0.5%) patients had 13 ribs bilaterally with an extra cervical rib on each side. Three (0.8%) patients had an extra unilateral cervical rib. In all, 1.4% of patients had extra cervical ribs.


CONCLUSIONS
The incidence of abnormal number of ribs in this normal population was 6.3%. When isolated, this finding is a normal variant.
Department of Obstetrics and Gynecology, Faculty of Health Sciences, Ultrasound Unit, Soroka University Medical Center, Ben-Gurion University of the Negev, Beer-Sheva, Israel. ralikah@bgu.ac.il
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R
Hershkovitz
D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging* / Q000453:epidemiology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D015994:Incidence; D007557:Israel / Q000453:epidemiology; D011247:Pregnancy; D011446:Prospective Studies; D012272:Ribs / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D016216:Ultrasonography, Prenatal / Q000379:methods*