Pregnant Obese Women and Fetal Ultrasound Quality.

Ultrasound (US) image construction uses equations that contain the value of the propagation velocity of sound waves; this velocity is assumed conventionally to be constant and equal to 1540 m/s in the human body. Since 1977, all manufacturers of US scanners have used this value, which was first established in 1950. In fatty tissue, however, the actual propagation velocity is only in the order of 1450 m/s. US velocity in fat tissue is slower than in other soft tissues (ie:1450 m/s vs 1540 m/s) therefore the intrinsic image quality in terms of sharpness and precision is improved when considering this parameter for image construction The main objective of this study is to evaluate the impact of ultrasound propagation velocity setting on completeness of ultrasound exams and images quality during the second and third trimester fetal ultrasound examination in obese patients.

Obese pregnant women will be included before the second trimester fetal ultrasound examination. Women will be allocated to one intervention group or to the control group. In the intervention group, the ultrasonographer will be able to use several ultrasound propagation velocities to perform the exam. In the control group, exam will be performed using the conventional ultrasound velocity. An exam will be considered to be complete if all the images recommended by national guideline are acquired. If ultrasound images are missing, other ultrasound exams may be performed until completeness is reached. The protocol will be applied for the second and the third fetal ultrasound examination which are recommended by national guideline. All scans will be evaluated by two independent experts who do not have performed any of the exams. They will evaluate the completeness of each exam. Each scan will be quoted using the quality score proposed by Salomon et al.