Objective To assess whether fetal brain structures routinely measured during the second and third trimester ultrasound scans, particularly the width of the cavum septi pellucidi (CSP), differ between fetuses small for gestational age (SGA), fetuses very small for gestational age (VSGA) and normal controls. Methods In this retrospective study, we examined standard ultrasound measurements of 116 VSGA, 131 SGA fetuses and 136 normal controls including the head circumference (HC), transversal diameter of the cerebellum (TCD), the sizes of the lateral ventricle (LV) and the cisterna magna (CM) from the second and third trimester ultrasound scans extracted from a clinical database. We measured the CSP in these archived ultrasound scans. The HC/CSP, HC/LV, HC/CM and HC/TCD ratios were calculated as relative values independent of the fetal size. Results The HC/CSP ratio differed notably between the controls and each of the other groups (VSGA P = 0.018 and SGA P = 0.017). No notable difference in the HC/CSP ratio between the VSGA and SGA groups could be found (P = 0.960). The HC/LV, HC/CM and HC/TCD ratios were similar in all the three groups. Conclusion Relative to HC, the CSP is larger in VSGA and SGA fetuses than in normal controls. However, there is no notable difference between VSGA and SGA fetuses, which might be an indicator for abnormal brain development in this group.
Keywords: cavum septi pellucidi; prenatal ultrasound; small for gestational age.