Conus medullaris migration during the third trimester: Aretrospective study.

Abstract

To explore the migration process of the conus medullaris (CM) and propose a normal range of CM levels during the third trimester. We retrospectively collected the ultrasonographic and clinical data of 588 fetuses during the third trimester. We located the CM and assigned scores. One-way analysis of variance and linear regression analyses were used to statistically analyze CM migration. Statistical significance was set at p<0.05. The CM levels were statistically different among the different gestational weeks of the third trimester. The CM level showed a linear regression correlation with the gestational weeks. On an average, the CM migrated from the top third of the L2 vertebra to the L1/2 intervertebral disc level. The CM continues to migrate, from the top third of the L2 vertebra to the L1/2 intervertebral disc level, during the third trimester. The term infant could have the CM at the normal adult level at birth. At the beginning of the third trimester, a CM located above the L2/3 intervertebral disc level could be normal; the CM location at the L3 vertebra level could be physiological and needs follow-up; and a CM presenting below the L3 vertebra level might indicate tethered cord syndrome. The fetus with a CM significantly above the L1/2 intervertebral disc level may have caudal regression syndrome.