Role of First-Trimester Ultrasound Screening for Central Nervous System Anomalies: A Single Center Study

Abstract

Objective

To evaluate potential sonographic features and a standardized protocol for ultrasound screening of different central nervous system (CNS) malformations in the first trimester and their follow up.

Methods

This was a single center prospectively collected data with retrospective analysis evaluating first-trimester scans for CNS malformations with standardized protocols performed between July 2017 and July 2023 involving 5,612 pregnancies. Follow-up at second and third trimester scans and post natal details were noted.

Results

We suspected or confirmed 36 cases with CNS abnormalities in 5,612 first trimester scans. Among those, 9 cases of exencephaly, 6 alobar holoprosencephaly, 2 isolated occipital encephalocele, 1 isolated hydrocephalus, 1 amniotic band syndrome, and 3 cases of open spina bifida were confirmed in first trimester scans. Three cases of Blake's pouch cyst, 2 cases of vermian hypoplasia, 1 with Dandy–Walker malformation, 1 with trisomy 21 (T21), one trisomy 18 (T18), 1 Meckel–Gruber syndrome, and 1 Joubert syndrome were suspected in first trimester scans and confirmed on follow up scans. Corpus callosal agenesis, corpus callosal dysgenesis, vein of Galen aneurysm, lobar holoprosencephaly, closed spinal dysraphism, and a massive cerebral hemorrhage and fetal infection were detected in second- and third trimester scans, which were normal at first trimester anomaly screening scan. With standard CNS planes, 69% of fetal CNS malformations were detected in our study. The sensitivity of our study was 69.7%, and the specificity was 99.89%.

Conclusion

Most of the major CNS abnormalities can be detected early in pregnancy. The first trimester is an ideal time for detection of CNS parameters, which is feasible and efficient and does not require any additional investigation time. Some CNS abnormalities manifest later in gestation and are not detected in the first trimester scan.

Keywords

first trimester anomaly scan - CNS anomalies - posterior fossa anomalies - Meckel–Gruber syndrome - Joubert syndrome

Publication History

Article published online:
17 July 2025

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