| Object In order to explore the imaging rate and the accuracy of positioning the fetal conus medullaris by a new 3D ultrasound method to detect atlantoaxial intervertebral space and compare with the traditional 2D ultrasound and 3D ultrasound methods.Material and MethodsConsecutively 318 pregnant women aged 18-43 years with single fetal were enrolled,who received routine ultrasound screening during the second trimester in our hospital.The average gestational age of fetal is 23 weeks ± 2.7 days.After using GE Voluson E8 three-dimensional ultrasound diagnostic apparatus,transabdominal 2D and transabdominal 3D volume probe to store 2D data and 3D volume data,GE 4D View software was used for off-line analysis.After obtaining the routine obstetric ultrasonography of 318 fetal,we use a new ultrasound method named detecting atlanto-axial intervertebral space in 3D ultrasound and raditional 2D and 3D ultrasound method to acquire and store the images.Three physicians with 5 years of work experience blindly analyzed the position of the fetal conus medullaris stored by three different methods on off-line software at different times.According to the different outcomes,318 cases were divided into normal group and abnormal group.The abnormal group of fetal were divided into tethered group and non-tethered group according to the presence or absence of tethered cord.(1)Analyze the relationship between the location of the fetal conus medullaris and the gestational age by detecting atlanto-axial intervertebral space in 3D ultrasound.The linear trend χ2 test of different grouping data with two-way ordered attributes is used to analyze the relationship of the position and the gestational age.(2)The χ2 test comparing multiple sample rates was used to compare the imaging rate between the normal and abnormal fetal in the three ultrasound methods.(3)The χ2 test comparing multiple sample rates was used to compare the differences between the three methods for the diagnosis of normal group and abnormal group.Results(1)318 fetal was enrolled in this study,including 276 in the normal group,and 42 in the abnormal group.The abnormal group contains 11 tethered cords and 31 non-tethered fetal.Totally 306 cases of the fetal conus medullaris were successfully located by the new method,including 267 cases in the normal group and 39 cases in the abnormal group.The traditional 2D ultrasound method was successful in 292 cases,including 258 cases in the normal group and 34 cases in the abnormal group;The traditional 3D ultrasound method was successful in 310 cases,including 270 cases in the normal group and 40 cases in the abnormal group.(2)In this study,the position of fetal conus medullaris in the normal group is located at L3 and above L3 in the second trimester,mainly at L2 and L2.5 level.The relationship between the position and the gestational age in the normal group was statistically analyzed.The linear trend χ2 test using different bidirectional ordered attributes of different grouping data showed that the linear regression component was statistically significant(χ2=75.80,P=0.000),the correlation coefficient(Spearman correlation)was 0.552(P=0.000),indicating that the position of fetal conus medullaris in the normal group was linearly related to the gestational age,and during the second trimester it increases with the growth of the gestational age.(3)The χ2 test comparing multiple sample rates was used to compare the imaging acquisition success rate of fetal conus medullaris by three ultrasound methods.Adjust the test level α’=0.05/4=0.0125,The results showed that there were no statistically significant differences between the three methods in the normal group imaging acquisition(χ2=7.39,P=0.025)and the abnormal group imaging acquisition(χ2=5.32,P=0.070).It indicated that all methods can successfully obtain the imaging of fetal spine and conus medullaris.(4)The χ2 test comparing multiple sample rates was used to compare the diagnosis correct rate of fetal conus medullaris position in normal groups by three methods,and adjust the test level α’=0.05/4=0.0125,the result shows there was no significant difference in the correct rate of conus medullaris position in the normal group(χ2=2.52,P=0.284).It indicated that three methods have high diagnostic value for the fetal conus medullaris position in the normal group.(5)The χ2 test comparing multiple sample rates was used to compare the diagnosis correct rate of the fetal conus medullaris in 11 cases of abnormal tethered cord group by three methods,and adjust the test level α’=0.05/4=0.0125,the difference was not statistically significant(χ2=1.22,P=0.543).It shows that three methods have high diagnostic value for the fetal conus medullaris position in the abnormal tethered cord group.(6)The χ2 test comparing multiple sample rates was used to compare the diagnosis correct rate of the fetal conus medullaris in 31 cases abnormal non-tethered group,and adjust the test level α’=0.05/4= 0.0125,the difference was statistically significant(χ2=9.87,P=0.007),which means that the new method has a higher accuracy rate for the diagnosis of fetal conus medullaris position in the abnormal non-tethered group.Conclusions Prenatal ultrasound has advantage in evaluating the fetal conus medullaris position.In this study,a new method named detecting atlanto-axial intervertebral space in 3D ultrasound was used for its higher imaging rate and the correct rate of positioning the fetal conus medullaris.In our study,in the normal group and abnormal tethered cord group,the above three methods can locate the fetal conus medullaris well while in the abnormal non-tethered group,the new method is better than traditional 2D and 3D methods.In conclusion,if fetal spinal abnormalities are found,it is still necessary to use a combined ultrasonic method to evaluate the position of fetal conus medullaris.When ultrasonic positioning fails,other methods such as MRI should be use to get a cottect position of fetal conus medullaris for early diagnosis of tethered cord. |
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