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

Abstract

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.