Eleven pairs of ribs of trisomy 18

Cervical ribs are more prevalent in stillborn fetuses than in live-born infants and are strongly associated with fetal aneuploidy

This study was undertaken to determine the prevalence of cervical ribs in stillborn fetuses undergoing autopsy at our institution and to search for significant associations with cervical ribs. European studies have reported an increased prevalence of cervical ribs in patients with childhood cancer and in stillborn fetuses. We reviewed data from autopsies performed at Primary Children's Medical Center, Utah, between 2006 and 2009 on 225 stillborns (≥20 weeks) and 93 deceased live-born infants (<1 year). Digital fetal radiographs in anterior-posterior and lateral views had been taken of each subject. Chi-square analysis and general linear models were used for statistical analysis of the data. The overall prevalence of cervical ribs was higher in stillborns than in live-borns who died in the first year (43.1% vs 11.8%). Karyotypes were available for 93 (41.3%) of the stillborns. Of those, cervical ribs were present in 33 of 76 (43.4%) stillborns with normal karyotype and in 13 of 17 (76.4%) stillborns with aneuploidy. Females with unavailable karyotypes were more likely to have cervical ribs than those with normal karyotypes (P  =  0.0002). This greater likelihood was not observed in males. Among the stillborns with normal karyotypes, we found no statistically significant association with gender or gestational age at fetal death. There was also no statistically significant association between congenital anomalies and the presence of cervical ribs. Our findings support the hypothesis that cervical ribs are markers for disadvantageous developmental events occurring during blastogenesis and have been subject to strong negative selection during evolution.

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.