OP14.05: Three‐dimensional sonography of the fetal posterior brain between 11 + 0–13 + 6 weeks gestation

Abstract

Short oral presentation abstracts (Lachmann et al., 2011). However, in our observation, the brain stem of spina bifida fetuses is characterized by kinking and thinning, rather than thickening. We examined the biometry and utility of these first trimester spina bifida markers in our population. Methods: Mid-sagittal facial images obtained at nuchal translucency screening between 11-0/7 and 13-6/7 weeks gestation were digitally stored. Normal (n = 500) and randomly interspersed spina bifida cases (n = 10) were analyzed by three blinded examiners. The BS was measured from the posterior border of the sphenoid bone to the anterior border of the fourth ventricle, and the BSOB from the latter to the anterior border of occipital bone, and adjusted for crown-rump length (CRL). Normality of distribution was confirmed with the Kolmogorov-Smirnov test, and means of spina bifida group and normals were compared by t-test. Results: BS diameter increased with CRL (R 2 = 0.14; P < 0.0001), whereas BSOB and BS/BSOB ratio decreased with CRL (R 2 = 0.168; P < 0.0001). BS diameter was significantly smaller in spina bifida fetuses (P < 0.0001; 4/10 cases below 5 th %ile, none above 95%ile), and BS/BSOB ratio was significantly higher in the spina bifida group (P < 0.002; 6/10 cases above 95 th %ile). With a 95% specificity, the above cutoff limits would yield a 40% and 60% sensitivity for SB detection, respectively. Conclusions: In our study population, spina bifida is associated with smaller brain stem diameters in comparison to normal first trimester fetuses. This would yield lower detection rates in screening with the BS/BSOB ratio than previously reported.