Objective: To analyze the ultrasonography (USG) values of median nerve cross sectional area (MN-CSA) in pregnant women with and without clinically diagnosed carpal tunnel syndrome (CTS). Design: Prospective cross-sectional study. Setting: Third trimester pregnant women during their routine office visits. Methods: USG was performed by a perinatologist and the MN-CSA at the carpal tunnel inlet was measured. Then, the participants were asked about the presence of typical CTS symptoms. Participants with typical clinical symptoms were assigned to the CTS group. Remaining participants were assigned to the Control group. Main outcome measures: The groups were compared according to MN-CSA. Results: Of the 89 pregnant women, 25 participants were grouped in CTS group and the remaining 64 participants were grouped in Control group. The MN-CSA was higher in the CTS group (9.44 ± 2.68) than in the Control group (7.20 ± 1.99), p = 0.00004. There was a statistically significant linear trend, p = 0.003, with higher MN-CSA associated with a higher proportion of patients diagnosed as CTS. Conclusions: USG measurement of MN-CSA at the wrist appears as a convenient method to confirm CTS diagnosis in pregnant women. Further research is necessary to determine a clear cut-off value for MN-CSA. Obstetricians can measure MN-CSA to confirm CTS diagnosis and consequently can offer conservative management, which is the widely accepted treatment modality in this cohort.