The ALDW classification for fetal insular morphology: gestational norms and screening utility

To observe the changes in fetal insular morphology with gestational age using the transverse thalamic view, and to preliminarily explore the value of this approach in cases with nervous system abnormalities. Pregnant women between 18 and 34 weeks of gestation who attended the Peking University First Hospital Ningxia Women and Children’s Hospital from June 2021 to August 2025 were enrolled. Standard transverse thalamic views were obtained, with particular attention paid to insular morphology. A total of 323 fetuses with normal neurodevelopment and 114 fetuses with concomitant nervous system abnormalities were ultimately included. Insular morphology in the normal group was classified into four types—arched-up (A), linear (L), dipped-down (D), and wavy (W)—using this ultrasonographic classification system, and the insular morphology of fetuses in the abnormal group was recorded accordingly. The differences in the distribution of insular morphology between the two groups were compared using the chi-square test. Logistic regression analysis was performed to evaluate the association between insular morphology and the presence of fetal nervous system abnormalities. Receiver operating characteristic (ROC) curve analysis was conducted to assess the diagnostic performance of insular morphology for identifying fetal nervous system abnormalities. In the normal group, the arched-up pattern was observed at 18–21 weeks, the linear pattern at 20–26 weeks, the dipped-down pattern at 25–31 weeks, and the wavy pattern at 28–34 weeks. When gestational age was treated as a continuous variable, the distribution of insular types differed significantly between the normal and abnormal groups ( P < 0.05). On multivariable logistic regression, conformity of insular morphology to gestational norms was a significant independent predictor of CNS anomalies ( P < 0.001). The ROC curve showed an AUC of 0.714 (95% CI: 0.657–0.770). Among the 114 cases in the abnormal group, 56 (49.1%) showed abnormal insular morphology. The manifestations of abnormal insular morphology included: absence of the insula, clearly abnormal insular shape, absence of the insular platform, an obviously shortened insular platform, and marked developmental delay or inconsistency with gestational age. Normal fetal insular morphology follows a regular evolution with gestational age. This simplified classification may serve as an auxiliary observational indicator in prenatal ultrasound screening.