VP28.05: Accuracy of qualitative and quantitative cranial utrasound signs at 11–14weeks in the screening of open spina bifida: systematic review, meta‐analysis

Objectives: To determine the position of the fetal conus medullaris (CM) in the first trimester of pregnancy. Methods: Multicentre prospective study including a non-consecutive series of normal fetuses at 11-13 weeks gestational age (CRL between 45 and 84mm). A volume dataset was acquired by transvaginal ultrasound starting from the midsagittal view of the fetal spine. All acquired volumes were processed to evaluate the level of the CM in relation to the fetal umbilical cord insertion, drawing a line perpendicular to the spine from the CM tip and reaching the anterior abdominal wall. The CM distance to the coccyx (CMCd) was also measured in all cases. Results: Overall, 130 fetuses were included in the study. In all cases the line showing the level of the CM encountered the anterior abdominal wall above or at the level of the cord insertion. A linear relationship (p = 0.002) was found between the CMCd and the fetal CRL. Mean CMCd was 1.09 ± 0.16 mm. Conclusions: Fetal CM seems visible at first trimester 3D ultrasound. In normal cases the CM level was never found below the fetal umbilical cord insertion, while the CMCd was noted to increase according to the gestational age.