Fetal Conus Medullaris Research Articles

Ultrasound-based horizontal ranging in the localization of fetal conus medullaris.

Currently, there are a variety of methods for ultrasound to localize the conus medullaris. A concern is that measured values can be influenced by variations in spinal flexion and extension. To overcome this limitation, the present study measures the horizontal distance (HD) between the end of the conus medullaris and the caudal edge of last vertebral body ossification in normal fetus at different gestational weeks, and analyzes the relationship between the measured value and fetal growth, as well as the utility of these measurements in assessing the position of the conus medullaris. A total of 655 fetuses at gestational weeks 18-40, who underwent routine prenatal ultrasound, were selected in the study. We measured the distance between the end of the cone of the fetal spinal cord and the caudal end of the final vertebral ossification center (Distance1, D1), the distance between the end of the spinal cord cone and the intersection of the extension of D1 with the caudal skin (Distance2, D2), and HD. We analyzed the correlation between the measurements and gestational weeks, established normal reference values, the ratio of D1, D2 and HD to the commonly used growth parameters was calculated. The ratios of D1, D2, HD and the application value of each ratio phase were analyzed, and the reliability analysis of repeated measurement results among physicians was performed. D1, D2 and HD exhibited strong linear correlations with gestational weeks. Among the ratios of D1, D2 and HD to common growth parameters, D2/FL stabilized after 20 weeks of gestation and consistently exceeded 1. Repeatability tests between D1, D2 and HD showed good reliability (P> 0.05). D1, D2 and HD are significantly correlated with gestational age. Horizontal distance measurement can effectively determine the position of fetal conus medullaris, enabling rapid prenatal evaluation of low position of conus medullaris and excluding the possibility of tethered cord.

Fetal Tethered Spinal Cord: Diagnostic Features and Its Association with Congenital Anomalies

Objective We assessed the frequency and type of associated congenital anomalies encountered with fetal tethered spinal cord (TSC) determined prenatally. Method A retrospective review was conducted based on the associated fetal abnormalities following diagnosis of low-lying fetal conus medullaris during the prenatal ultrasound. Results Of the 26 fetuses with low-lying conus medullaris, four were solitary TSC and 22 had TSC combined with associated congenital malformations, including four cases with spina bifida occulta, four cases with spina bifida aperta, one case with severe hydrocephalus, and 13 cases with multisystem congenital malformations. Among all the 13 cases with combined multisystem congenital malformations, four cases had vertebral defects, anal anomalies, cardiac defects, trachea-esophageal fistula, renal anomalies, and limb anomalies (VACTERL) syndrome, two cases had combined kidney development abnormalities, one case had cloacal exstrophy (OEIS syndrome), and six cases had chromosomal abnormalities (one case of chromosome 7q deletion, two cases of trisomy 13 syndrome, one case of trisomy 18 syndrome, one case of trisomy 9 syndrome, and one case of chromosome 4p deletion). Conclusions Low-lying conus medullaris found during prenatal ultrasound examination were often associated with neural tube malformations or multi-systemic complex developmental malformations. The frequency of chromosomal abnormalities was 23.1%.

Gestational age-specific reference standards of low-lying conus medullaris level in fetuses: a prospective cohort study.

To explore the position change of fetal conus medullaris by ultrasound, and to propose gestational age-specific references for the lower limits of fetal conus medullaris level. We prospectively collected the imaging and clinical data of fetuses whose mothers accepted routine prenatal ultrasonic follow-ups in the Department of Medical Ultrasonics, Chinese PLA General Hospital, between November 2020 and April 2021. By assigning to the conus medullaris levels, calculating statistical data, and performing linear regression analysis, we determined the correlation between the conus medullaris level and gestational week, as well as between the 95th percentile of the conus medullaris level, i.e., the lower limit of the conus medullaris level, and gestational week. We included 1202 different fetuses at 17-40 gestational weeks in the study. Both the conus medullaris level and the 95th percentile of the conus medullaris level were linearly correlated with gestational week. We calculated the adjusted values of the lower limits of fetal conus medullaris levels, that is, the theoretical references of the lower limits, according to the linear regression equation, and composed a comparison table. The fetal conus medullaris position continues changing cranially with gestational weeks during the whole pregnancy. The conus medullaris of a term fetus should not lie below the L2 vertebra level at birth. We proposed reference criteria of fetal low-lying conus medullaris for each gestational week from 17 to 40weeks of gestational age, which potentially help prompt diagnosis and improve prognosis of fetal tethered cord syndrome.

OC01.04: Determination of the normal fetal conus medullaris level throughout pregnancy by a novel three‐dimensional rendering technique

OC01.04: Determination of the normal fetal conus medullaris level throughout pregnancy by a novel three‐dimensional rendering technique

Three-Dimensional Sonographic Evaluation of the Position of the Fetal Conus Medullaris at First Trimester

Objective: The objective of this study was to assess the position of the conus medullaris (CM) at the first trimester 3D ultrasound in a cohort of structurally normal fetuses. Methods: This was a multicenter prospective study involving a consecutive series of structurally normal fetuses between 11 and 13 weeks of gestation (CRL between 45 and 84 mm). All fetuses were submitted to 3D transvaginal ultrasound using a sagittal view of the spine as the starting plane of acquisition. At offline analysis, the position of the CM was evaluated by 2 independent operators with a quantitative and a qualitative method: (1) the distance between the most caudal part of the CM and the distal end of the coccyx (CMCd) was measured; (2) a line perpendicular to the fetal spine joining the tip of the CM to the anterior abdominal wall was traced to determine the level of this line in relation to the umbilical cord insertion (conus to abdomen line, CAL). Interobserver agreement for the CCMd was evaluated. Linear regression analysis was used to determine the association between the CMCd and CRL, and a normal range was computed based on the best-fit model. The absence of congenital anomalies was confirmed in all cases after birth. Results: In the study period between December 2019 and March 2020, 143 fetuses were recruited. In 130 fetuses (90.9%), the visualization of the CM was feasible. The mean value of the CMCd was 1.09 ± 0.16 cm. The 95% limits of agreement for the interobserver variability in measurement of the CMCd were 0.24 and 0.26 cm. The interobserver variability based on the intra-class correlation coefficient (ICC) for the CCMd was good (ICC = 0.81). We found a positive linear relationship between the CCMd and CRL. In all these fetuses, the CAL encountered the abdominal wall at or above the level of the cord insertion. Conclusion: In normal fetuses, the assessment of the CM position is feasible at the first trimester 3D ultrasound with a good interobserver agreement. The CM level was never found below the fetal umbilical cord insertion, while the CMCd was noted to increase according to the gestational age, confirming the “ascension” of the CM during fetal life.

Prenatal ultrasound diagnosis of neural tube defects in the era of intrauterine repair – Eleven years’ experiences

ObjectiveTo modify the current neural tube defect (NTD) classification for fetal medicine specialists, and to investigate the impact of prenatal ultrasound conus medullaris position screening on the detection rate of closed spinal dysraphism and pregnancy outcomes. Materials and methodsThe clinical data of 112 patients prenatally diagnosed with neural tube defects in Taiji clinic from 2008 to 2018 were retrospectively analyzed. All cases were classified following the modified classification. We compared the detection rate before and after introducing the conus medullaris screening and pregnancy outcomes for NTD types. ResultsClosed spinal dysraphism type prevailed in our sample (43.8%). The median gestational age at the time of detection for cranial dysraphism was 13.3 weeks, open spinal dysraphism was 22.0 weeks, and closed spinal dysraphism was 22.6 weeks. All cranial dysraphism (n = 43) and open spinal dysraphism cases (n = 20) had pregnancies terminated. For closed spinal dysraphism Class 1, the live-birth rate was 100.0% in the cases without other anomalies and 33.3% in the cases with other anomalies, respectively (X2 = 17.25, p < 0.001). Similarly, for Class 2, pregnancy continuation rate was 50.0% in cases without other anomalies and 20.0% in cases with other anomalies, yet it failed to reach statistical significance (X2 = 0.9, p = 0.524). ConclusionOur case series may help to improve early screening and prenatal diagnosis of NTDs. Modified classification is adjusted for use in ultrasound fetal care facilities, which could be used for predicting pregnancy outcome. We suggest promoting first-trimester anatomical screening in order to make an earlier diagnosis and therefore provide better prenatal care for open spinal dysraphism cases in the era of intrauterine repair. Our findings imply that the use of fetal conus medullaris position as a marker for closed spinal dysraphism improves the detection rate and would unlikely lead to a higher termination rate.

Study of positioning of fetal conus medullaris by detecting atlanto-axial intervertebral space with three-dimensional ultrasound

Objective To explore the imaging rate and diagnostic rate of positioning the fetal conus medullaris by three-dimensional ultrasound method to detect atlantoaxial intervertebral space, comparing it with the traditional two-dimensional and three-dimensional ultrasound methods. Methods Consecutively 318 singleton fetuses received routine ultrasound screening during the second trimester were enrolled from November 2017 to December 2018 in Shenzhen Luohu People′s Hospital and Shenzhen People′s Hospital. These fetuses included 276 normal cases and 42 abnormal cases. The abnormal group contained 11 cases tethered cords fetuses(tethered cords group) and 31 cases non-tethered fetuses(non-tethered group). A new ultrasound method named detecting atlanto-axial intervertebral space with three-dimensional ultrasound and traditional two-dimensional and three-dimensional ultrasound methods were used to acquire and store the images. The positions of the fetal conus medullaris were analyzed blindly and recorded by three experienced physicians using three different methods with off-line software. Results ①The χ2 test comparing multiple sample rates was used to compare the imaging acquisition success rate of fetal conus medullaris by three ultrasound methods. The test level was adjusted to be α′=0.05/4=0.0125, the results showed that there were no statistically significant differences between the three methods in the normal group (χ2=7.39, P=0.025) and the abnormal group (χ2=5.32, P=0.070). ②The χ2 test comparing multiple sample rates was used to compare the diagnostic accuracy of fetal conus medullaris position in normal group by three methods, it showed there was no significant difference in the correct rate of conus medullaris position in the normal group (χ2=2.52, P=0.284). ③The χ2 test comparing multiple sample rates was used to compare the diagnostic accuracy of the fetal conus medullaris in tethered cord group and non-tethered group using 3 methods, the difference was not statistically significant in tethered cord group (χ2=1.22, P=0.543), while the difference was statistically significant in non-tethered group(χ2=9.69, P=0.008). Conclusions The method of detecting atlanto-axial intervertebral space with three-dimensional ultrasound has a high imaging rate and diagnostic accuracy in positioning the fetal conus medullaris. Positioning of fetal conus medullaris by detecting atlanto-axial intervertebral space with three-dimensional ultrasound is better than traditional two-dimensional and three-dimensional ultrasound in the abnormal non-tethered fetuses, which can provide more valuable information for prenatal diagnosis consultation and prenatal and postnatal care. Key words: Ultrasonography; Atlanto-axial intervertebral space; Fetal conus medullaris; Tethered cord

OP13.07: Prenatal assessment of fetal conus medullaris in cases with closed spinal dysraphism

OP13.07: Prenatal assessment of fetal conus medullaris in cases with closed spinal dysraphism

Prenatal Assessment of the Position of Fetal Conus Medullaris as a Predictor of Fetal Spinal Lesions

The aim of this study is to compare two different methods in assessment of the position of fetal conus medullaris (CM) and to explore the significance for assessment of CM. This study included both normal fetuses and those with the diagnosis of fetal spinal lesions. The position of fetal CM was performed sonographically using two methods: location of CM in relation to the vertebral body (CM level) and measurement of the conus sacrum (CS) distance. The results showed that intra-observer and interobserver concordance was high for the two methods, both in the normal and abnormal groups. There was significant association between femur length and CS distance (R2 = 0.917) and between gestational age and CS distance (R2 = 0.892). We propose the combined use of CM level location and CS distance measurement for the prenatal diagnosis of fetal spinal lesions for complementary needs.

Localization of the fetal conus medullaris by oblique view extended imaging.

To evaluate the accuracy of oblique view extended imaging (OVEI) in locating the position of the fetal conus medullaris. One hundred and twenty-two normal fetuses and five counterparts with spinal bifida received prenatal ultrasound examination. The vertebral body at the terminal of the conus medullaris and the coronal section of over five vertebral bodies were reconstructed using OVEI. Development of the nervous system of normal fetuses was assessed at postnatal day 28. For spinal bifida cases, pathological examination was performed. Among 127 fetuses, the conus medullaris was accurately positioned in 120 (94.0%) cases according to OVEI. OVEI failed to locate the conus medullaris in three healthy fetuses due to obesity of the mother and four cases with spinal bifida due to abnormal fetal position. The conus medullaris was located at L3 or above in 115 healthy fetuses. The conus medullaris was positioned below L4 in five fetuses with spinal bifida, including L5 in two, S1 in two, and S3 in one, which was consistent with the findings of pathological examination. OVEI can display the 12th rib, T12, and conus medullaris simultaneously. OVEI is applicable to precisely locate the position of the conus medullaris and useful for prenatal evaluation of spinal bifida.

Sonographic Evaluation of Fetal Conus Medullaris and Filum Terminale

Background: Sonographic evaluation of the fetal conus medullaris (CM) level is not reproducible. The objectives of this study were to determine the normal position of the fetal CM during pregnancy as well as the normal intradural filum terminale (FT) length and to evaluate their use in detecting tethered cord. Methods: This is a prospective evaluation of normal singleton pregnancies examined by sonography from 17 weeks of gestation to term. Each sonographer had to identify the top of the first sacral vertebra (S1) to measure the distance between it and the conus extremity (CM-S1 distance). The intradural FT distance was measured with 5- to 8-MHz probes. Results: 194 consecutive pregnant women were included. The CM and intradural FT were demonstrated clearly in 164 (84%) cases. The mean CM-S1 distance was 20.6 mm (range 0.5-42). The mean intradural FT distance was 27.9 mm (range 6.6-49.3). Linear regression analysis showed a significant association between both those distances and gestational age (p < 0.05). In cases of tethered cord, the mean CM-S1 distance and the mean intradural FT distance were both below the 5th percentile. Conclusion: Prenatal evaluation of the CM and the intradural FT is feasible and reproducible and seems useful in detecting tethered cord.

Prenatal Evaluation of the Fetal Conus Medullaris on a Routine Scan

Objective: To assess the ability to identify the conus medullaris (CM) and measure the conus-sacrum distance (CS distance) on a routine scan and the relationship with maternal and fetal factors. Methods: This was a prospective study. The assessment of the CM and the CS distance and the influence of the body mass index (BMI), gestational age (GA) and fetal position were analyzed. The correlation between the femur length (FL) and the GA with the CS distance was evaluated. Results: A total of 696 fetuses were analyzed. The CM could be visualized in 82.3% of the cases, and the CS distance could be analyzed in 81.2% of the cases. The CM assessment was statistically associated with BMI and fetal position but not with GA. The CS distance assessment was statistically associated with BMI and GA but not with fetal position. We determined a significant association between the FL/CS distance and between the GA/CS distance. Conclusions: Assessment of the CM is possible on most routine scans. The CS distance could be introduced to routine scans for the assessment of prenatal skin-covered spinal dysraphism. High BMI, advanced GA and breech presentation could be potential factors limiting the feasibility of evaluating the CM.

Ultrasonography quantitative indicator for position of fetal conus medullaris

Objective To determine the normal position of the fetal conus medullaris and assess its clinical significance. Methods A total of 550 singleton pregnant women who were examined by fetal ultrasonography in the Department of Ultrasound at the Second Hospital of Fujian Medical University from June 1,2013 to September 31, 2014 were included. Inclusion criteria were pregnancies with regular menstruation cycle and known last menstrual period, gestational age (GA) confirmed by ultrasonographic examinations, and neonate abnormality excluded by pediatrician after born. Routine obstetric ultrasound examinations were performed to measure the biparietal diameter (BPD), femur length (FL), head circumference (HC) and abdominal circumference (AC). The conus distance (CD) was determined by measuring the distance between the distal end of the conus medullaris and the caudal end of the last vertebra. The average value was calculated for each group according to GA. Fifty normal fetuses were randomly selected for quality control. For inter-observer reliability assessment, the same data were collected and analyzed by two different operators. For intra-observer reliability assessment, the data were collected and analyzed twice by the same operator with an interval of half an hour. Linear regression correlation analysis was performed to analyze the relationship between CD and GA, BPD, FL, HC and AC. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to analyze the repeatability of the analysis. Results In 518 (94.2%) of 550 fetuses, the CD was successfully measured. Positively correlations between the conus distance and the gestational age was observed. The CD was (10.0±3.3) mm at >14-≤15 weeks (n=17), (27.7±3.8) mm at >20-≤21 weeks of gestation (n=18), (41.5±2.4) mm at >26-≤27 weeks (n=8), (54.7±3.0) mm at >32-≤33 weeks (n=17), and (71.9±2.7) mm at >41-≤42 weeks (n=6). Linear regression correlations between CD (mm) and FL, AC, HC, BPD and GA were: CD=1.04× FL (mm)-8.71, CD=0.23× AC (mm)-10.11, CD=0.28× HC (mm)-18.10, CD=0.90× BPD (mm)-17.65, CD=2.34× GA (weeks) -20.94 (r=0.990, 0.985, 0.978, 0.974 and 0.973, respectively, all P<0.01). The measurement of the conus distance exhibited good reproducibility between different operators (ICC=0.984, 95%CI: 0.972-0.991) and for the same operator (ICC= 0.992, 95%CI: 0.985-0.995) with the 95% limits of agreement of -1.8 to 3.5 mm and -4.3 to 2.1 mm. Bland-Altman analysis showed that most of the measured values were within 95% confidence interval suggesting good consistency. Conclusions The distance, between the end of the conus medullaris and the end of the last vertebral body under ultrasound scan, is positively correlated with FL and other ultrasonographic indicators, which implies that it could be used as a new index for position of fetal conus medullaris. Key words: Spinal cord; Ultrasonography, prenatal; Sacrum

Prenatal evaluation of the conus medullaris position in normal fetuses and fetuses with spina bifida occulta using three‐dimensional ultrasonography

This study aimed to assess the fetal conus medullaris (CM) position with three-dimensional (3D) ultrasonography and its use in detecting and diagnosing spina bifida occulta (SBO). We examined 150 normal fetuses (gestational age, 20-38 weeks) and 14 fetuses with SBO. All fetuses underwent prenatal 3D ultrasonography, and the CM position in relation to the vertebral body was evaluated using volume contrast imaging. Intra- and inter-observer agreements were assessed using weighted kappa. The correlation between gestational age and CM level was determined by linear regression analysis. Operators successfully located the CM position in 145 cases. The CM was at L3 or higher in all normal group cases. A linear relationship was noted between gestational age (X) and CM position (Y) (Y = 0.118X + 6.011, R(2) = 0.679, P < 0.001). The weighted kappa values for intra- and inter-observer agreement were 1.0 and 0.788, respectively. The CM was located at L3 in one case and lower than L3 in 13 cases in the SBO group. All values were below the fifth percentile for the normal group. Three-dimensional ultrasonography may accurately determine the CM vertebral level. Prenatal evaluation of the CM position may improve the detection and diagnosis of SBO.

Fetal magnetic resonance imaging of normal spinal cord: evaluating cord visualization and conus medullaris position by T2-weighted sequences.

Prenatal magnetic resonance (MR) imaging demonstration of the normal spinal cord and the conus medullaris location has not been well studied. We compared balanced fast field echo (bFFE) with single-shot turbo spin-echo (SSh-TSE) MR sequences for visualizing the normal spinal cord and position of conus medullaris in fetuses. This retrospective study was approved by the Institutional Review Board of Chang Gung Medical Foundation. We reviewed the MR images of 141 fetuses aged between 16 and 39 gestational weeks, to determine the position of the conus and visualize the spinal cord by using a signal intensity ratio of cerebral spinal fluid (CSF) to the spinal cord. Of the 75 subjects having normal spinal cord and being examined by both bFFE and SSh-TSE studies, the signal intensity ratio of CSF/cord was greater on bFFE images (2.18 ± 0.53) than that on SSh-TSE images (1.21 ± 0.13) (p < 0.05). The conus level identified in the 50 subjects, in whom the lumbosacral spine was appropriately imaged, was located from L1 to L5 levels. The ascendance of the conus correlated moderately with gestational age. With greater signal contrast ratio of CSF to spinal cord, bFFE sequence, when compared with SSh-TSE sequence, provides better visualization of normal spinal cord. The fetal conus medullaris ascends from L5 to L1 levels as the gestational age increases.

OP05.08: Prenatal evaluation of the conus medullaris position in normal fetuses and fetuses with spina bifida occulta with three‐dimensional ultrasound

To determine the position of the fetal conus medullaris (CM) in relation to vertebral body by using three dimensional ultrasound (3D US) from 20 to 32 gestation weeks. To compare the difference of CM position between normal fetuses and fetuses with spina bifida occulta. Two operators independently positioned CM in relation to vertebral body by using 3D US with VCI mode (Figure) in 30 fetuses. Intra- and inter-observer agreements were assessed. The CM position was evaluated in 102 normal fetuses (normal group) and 11 cases with prenatally diagnosed spina bifida occulta (abnormal group) with 3D US. The intra- and inter-observer agreements of CM positioning by 3D US are good, with the Weighted Kappa value 1.0 and 0.788, respectively. The CM position can be determined in 97 of the 102 cases. Linear relationship between CM position and gestational age is established in normal group. The CM position in relation to vertebral body is higher than L3 in all normal fetuses, whereas that is below L3 in all abnormal cases. Supporting information can be found in the online version of this abstract Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Prenatal evaluation of the position of the fetal conus medullaris

To determine the position of the fetal conus medullaris during pregnancy in relation to the last vertebral body and to examine its use in detecting skin-covered spinal dysraphism. This was a retrospective study involving 300 consecutive ultrasound examinations between 15 weeks of gestation and term. Two operators independently assessed images of the spine to determine whether the conus medullaris and the last vertebral body could be visualized in a single image in a midsagittal plane. The distance between these two landmarks (the conus distance) was measured twice by both operators who were not aware of any previous measurements. Intra- and interobserver variability was assessed by 95% limits of agreement. Linear regression analysis was used to determine the relevant contributors to the conus distance and a normal range was computed based on the best-fit model. The normal results were compared with five cases of prenatally detected skin-covered spinal dysraphism. In 84.7% of the 300 cases, both operators were able to visualize the conus medullaris and the last vertebral body. Ninety-five percent limits of agreement for the intraobserver variability in measurement of conus distance were ± 1.9 mm. For the interobserver variability, they were - 3.7 and 2.5 mm. We found a linear relationship between conus distance and gestational age, biparietal diameter and abdominal circumference. The strongest relationship was observed for femur length (conus distance = - 8.2 + femur length (mm)). In the five abnormal cases, conus distance was well below the 5(th) percentile. Determination of conus distance allows for an objective and feasible assessment of the conus medullaris position. This parameter promises to be useful in the prenatal detection of skin-covered spinal dysraphism.

Sonographic evaluation of the fetal conus medullaris at 20 to 24 weeks' gestation

To determine the normal level of the conus medullaris (CM) of the spinal cord of normal fetuses at 20 to 24 weeks' gestation using abdominal sonography. Using a 4 to 8 MHz ultrasound abdominal transducer, CM was imaged in the midsagittal plane with the fetal spine facing toward the transducer. The CM ending level was located by counting the vertebrae caudal starting at T12, which was identified by lowest fetal rib. The CM locations were defined according to their positions relative to the vertebrae. One hundred and ten consecutive pregnant women were included in the study. The CM was clearly demonstrated in 78 (71%) of these cases. Most of the scanned fetuses had the CM ending height adjacent to vertebrae L2, L2-3 inter-space and L3 (73/78, 93%). The L1-2, L2, L2-3, and L3 vertebral groups did not differ in mean gestational weeks, maternal age, or fetal gender. The level of the CM can be determined at 20 to 24 weeks' gestation in about 70% of fetuses. Most of the scanned fetuses had the CM ending height adjacent to vertebrae L2, L2-3 vertebral space, and L3 (73/78, 93%). When detected lower than the third lumbar vertebra it should prompt prenatal and postnatal surveillance.

Sonographic examination of the fetal central nervous system: guidelines for performing the ‘basic examination’ and the ‘fetal neurosonogram’

Sonographic examination of the fetal central nervous system: guidelines for performing the ‘basic examination’ and the ‘fetal neurosonogram’

P13.29: Location of the conus medullaris in nomal fetuses

To establish the normal location of the fetal conus medullaris in China. The study include 828 expectant mothers who have single normal fetus. The fetal gestation ages are from 18 weeks to 40 weeks. We examined on lower spine with 3.5–5.0MHz ultrasound probe to determine the position of conus medullaris. Terminals are related to their correspondingly vertebral level and marked with numeral. The range of normal position and mean position were calculated, and the comparison with positions was made in different gestational weeks. The regular of the raise about the fetal conus medullaris and the relevant factors which may influence the position of the conus medullaris were analyzed. The peak of the raising about the fetal conus medullaris is in the 18 ∼ 21 weeks, afterwards, the fetal conus medullaris rise slowly. The fetal conus medullaris reach the level of L3 at 21 weeks gestation, and L2 to L3 that of 22–28 weeks, and L1 to L2 that of 29–40 weeks. The position of conus medullaris terminal has negative relation with BPD HC AC and FL. With the fetal gestation age increased, the position of fetal conus medullaris is raising. The peak of the raise about the fetal conus medullaris is in the fetal period, particularly before 21 weeks. When the babies were born, the mean position of the conus medullaris approached to the adult level of L2, which is obviously higher than the known level of L3.