Use of a Pocket-sized Ultrasound Machine (PUM) for Routine Examinations in the Third Trimester of Pregnancy

Objectives: To evaluate the application of a pocket-sized ultrasound machine (PUM) in a routine antenatal third-trimester scan compared with a high-specification ultrasound machine (HSUM).

Methods: This was an observational cohort study of 53 unselected women who came for their routine third-trimester ultrasound scan. The first scan was performed by an experienced ultrasonographer on an HSUM for fetal growth, fetal wellbeing and placental location. A second experienced operator performed the measurements on the PUM. Both operators were blinded to the other's findings and measurement results.

Results: Fifty-one patients were eligible and scanned at a median gestational age of 31 + 1 (range, 27 + 2 to 36 + 0) weeks. Mean pregestational body mass index was 22.9 ± 3.1 (range, 17.6-35.7) kg/m(2) . In the comparison between measurements made using the PUM and HSUM, perfect agreement was found for fetal position, fetal bladder and stomach visualization (all κ 1.0) and very good agreement was found for placental position (κ 0.86). Measurements of deepest vertical pocket correlated moderately (intraclass correlation coefficient (ICC) 0.38 (95% CI, 0.12-0.59); Bland-Altman bias, 2.43 (95% limits of agreement (LoA), -22.65 to 27.51)). For fetal growth measurements there was very good agreement for biparietal diameter (ICC, 0.93 (95% CI, 0.88-0.96), Bland-Altman bias, -1.06 (95% LoA, -5.07 to 2.95)), and good agreement for femur length (ICC, 0.66 (95% CI, 0.48-0.79), Bland-Altman bias 0.56 (95% LoA, -5.97 to 7.08)) and transcerebellar diameter (ICC, 0.65 (95% CI, 0.46-0.78), Bland-Altman bias, -0.84 (95% LoA, -7.77 to 6.09)).

Conclusion: A battery-driven PUM can be used in third-trimester obstetrics for routine assessment of fetal growth (biparietal diameter, transcerebellar diameter and femur length) and for assessment of fetal wellbeing.