Transvaginal ultrasonographic definition of the central nervous system in the first and early second trimesters.

A 6.5 MHz transvaginal sector scanner was used to describe the fetal central nervous system anatomy from 6 to 14 weeks. One hundred thirty-three pregnant patients were scanned after the crown-rump measurements were found to be within a range of less than or equal to 4 days from menstrual age. The number of possible ultrasonographic sections ("slices"), as well as the number of successful views in the axial, coronal, and sagittal sections, was tabulated. A detailed list of central nervous system structures that are seen at each gestational age is presented. The results showed that a significant number of brain structures could be imaged. The number and the clarity of the structures and the number of successful views in the three scanning planes increased with gestational age. We concluded that transvaginal scanning for central nervous system maldevelopment can be started in the late first and early second trimesters.