P-761 Four-dimensional ultrasound using an electronic probe to guide embryo transfer: a feasibility study
Authors: Vasquez Carlon D , Rouleau J  P , Guerrero J , Rodriguez A , Costa M , Hernandez J , Naftolin F , Palumbo A 
Published: July 2024

Abstract

Study question
Is four-dimensional ultrasound (4D-US) guided embryo transfer feasible and safe?

Summary answer
4D trans-abdominal US with electronic probe is feasible and safe and justifies a formal study for non-inferiority to two-dimensional ultrasound (2D-US) for embryo transfer guidance.

What is known already
The use of 2D-US to guide embryo transfer is the usual procedure (Eshre/ASRM guidelines, evidence A), and investigations of the benefits of 3D and 4D-US have been inconclusive. 3D-US can locate the embryo flash in the coronal plane immediately after performing embryo transfer but furnishes only retrospective information. 4D-US requires two operators at transfer, and there has been slow image acquisition and poor image quality, not allowing satisfactory comparison of accuracy and precision with other methods.

Study design, size, duration
Using a high-end ultrasound device (Voluson E10, GE Healthcare, Zipf, Austria) with an electronic 3D-4D probe (eM6C G2), a prospective observational trial with 29 women undergoing mock embryo transfer in a private infertility clinic was performed between October 2023 and January 2024. Exclusion of subjects included BMI greater than 35 (3 cases) and an intramural myoma that impeded 4D-US visualization (3 cases).

Participants/materials, setting, methods
Two operators expert in U/S performed each procedure. Electronic probe settings were adapted for each subject. To simulate the embryo transfer, a Wallace catheter containing air and fluid was inserted and monitored transabdominally by 4D-US using the electronic probe. The catheter was observed until it reached 1 cm from the fundus and the embryo flash (bubble) identified. Entrance through the cervix was controlled by 2D and 4D.

Main results and the role of chance
The following variables were recorded: age, BMI, cycle day, use of hormones, endometrial thickness, position of the uterus, presence of fibroids, image quality, difficulty of entrance, visualization of the cervix. The 23 subjects had the following characteristics: mean age 39±6.4, BMI 24.14±4.4. Image quality was optimal in 18 patients and due to a retroverted uterus was suboptimal in 5 subjects. Cannulation of the cervix was difficult in 1. Eight patients were on birth control pills and 15 were on day 6-10 of spontaneous cycles. The mean endometrial thickness was 7.13±3mm. Mean hysterometry was 7.10±0.9mm. Visualization of the cervix with 4D-US was good in 12 subjects, fair in 7 and poor in 4. Visualization of the catheter in the cavity with 4D-US was good in 16 subjects, fair in 2 and poor in 5. The embryo flash was adequately visualized by 4D-US in 18 subjects and less well in 5. Catheter position was correctly identified by comparison 3D-US in 20/23 subjects. There were no adverse effects during or following the procedure.

Limitations, reasons for caution
Patients with poor image quality, due to obesity, retroverted uterus or fibroids, are not candidates for this technique. The need for two operators limits the practicability of the procedure, increasing the need to show its superiority over the usual practice before it could be adopted clinically.

Wider implications of the findings
4D-US for embryo placement is feasible and safe. Studies that compare the accuracy and precision of 4D-US vs 2D-US to guide embryo transfer and the cost/benefit ratio of 4D ultrasound guided embryo transfer are in order..

Trial registration number
not applicable for non-clinical trials