Abstract:

Objective

To evaluate the predictive value of fetal craniofacial ultrasound markers for open spina bifida (OSB) during early pregnancy (gestational weeks 11-13⁺⁶).

Methods

The medical data of 13 fetuses with OSB and 60 normal fetuses that underwent prenatal examinations at Beijing Obstetrics and Gynecology Hospital, Capital Medical University from December 2018 to November 2023 were retrospectively reviewed and analyzed. Based on prenatal ultrasound quality control standards, standard sections of early pregnancy ultrasound were selected. The mid-sagittal section of the craniofacial region was assessed for morphology of the interbrain,midbrain, brainstem, fourth ventricle, and posterior fossa cistern. Measurements included brain stem width(BSW) and the distance from the brainstem posterior edge to the occipital bone (BSOB). The BS/BSOB ratio was calculated, and the frontomaxillary facial angle (FMFA) was evaluated. Qualitative indicators such as the maxilla-occipital line (MO line) in relation to the junction of the thalamus and midbrain (J-TM) were observed.Measurements on the lateral ventricle transverse section included the ratio of choroid plexus length to occipitofrontal diameter (CP-L/OFD), choroid plexus area, and the ratio of choroid plexus area to lateral ventricle plane brain area(CP-A/HA). The t-test or rank sum test was used to compare the differences in the above indexes. Lasso regression was used to screen the indexes to establish a prediction model. Receiver operating characteristic (ROC) curves of each index and the prediction model were drawn to evaluate the predictive value of each index for OSB in fetuses.

Results

In the mid-sagittal plane of the head and face, the diencephalon and mesencephalon of 60 normal fetuses exhibited an “8-shaped” morphology. The brainstem, fourth ventricle, and posterior fossa structures were clearly visible, appearing as three nearly parallel cavities. The J-TM was located above the MO line. In 13 OSB fetuses,the diencephalon and mesencephalon were distorted, the brain stem was displaced downward and widened, the BSOB was narrowed, and the fourth ventricle was compressed and reduced in size. Among these fetuses, the fourth ventricle disappeared in 10 cases (76.9%), leading to the presence of two cavities. In 11 cases (84.6%), the J-TM was below the MO line. Compared to the normal group, the OSB group showed a statistically significant increase in BSW/BSOB [1.26 (0.79, 1.49) vs 0.57 (0.52, 0.65); Z=18.09, P＜0.001] and a statistically significant decrease in the FMFA [77.60° (67.05°, 84.22°) vs 85.09° (80.15°, 89.03°); Z=6.48, P=0.009]. Lasso regression analysis showed that BSW/BSOB, FMFA, and CP-A/HA were significant variables for predicting OSB. Based on these variables, a regression model was established, and the regression equation was log(P/1-P) =2.043BSW/BSOB-0.026FMFA+1.251CP-A/HA-12.414. The ROC curves of each index and the regression model were plotted, and the area under the curve of the predictive model was 0.928, indicating good diagnostic performance compared to other indexes.

Conclusion

Ultrasound markers obtained from routine sections in fetuses at 11-13⁺⁶ gestational weeks can effectively predict fetal OSB. BSW/BSOB, FMFA, and CP-A/HA are significant variables for predicting OSB, and their combination provides better diagnostic value for OSB.

Key words: Open spina bifida, First trimester, Prenatal diagnosis, Ultrasound markers