Detection rate of fetal CNS anomalies by first and second trimester ultrasound screening

Objectives The aim of this study was to detect CNS abnormalities in first and second trimester by ultrasound. Methods This cross-sectional study was performed on pregnant women who referred to the radiology department of Imam Reza and Valiasr hospitals in Tehran-Iran during 2019-2020. After obtaining informed consent, pregnant women were screened in the first trimester at week 13-13 and then in the second trimester at week 18-20 by a 5-8 MHz Ultrasound Transducer. Each ultrasound included examination of the fetal brain and vertebrae at the axial coronal and sagittal planes in the most important anatomical areas, including the trans-thalamic (TT) or the trans-ventricular (TV) plane, transverse cerebellar, and vertebral canal plan. Ultrasound of the first and second trimesters of all mothers was performed. Information of all pregnant mothers was collected and recorded. Data analysis was performed using SPSS software version 25. Results In this study, 2234 pregnant women were included in the study. The total rate of detected anomalies was found to be 1.3%. The rate of abnormalities detected in the first trimester was far less than in the second trimester. The prevalence of CNS anomalies in the population under 30 years of age was also found 0.9%, while it was 1.6% in the population over 30 years of age. Conclusion Second trimester ultrasound is the method of choice in diagnosing central nervous system abnormalities. However, first trimester ultrasound is the diagnostic method for structural abnormalities of the skull.