4D ultrasound as a method to assess uterine peristalsis.

Objective: To study uterine peristalsis using step-by-step 4-dimensional (4D) ultrasound assessment video, explore its relationship with progesterone levels in a select in vitro fertilization population, and assess the reproducibility of the technique.

Design: Four-dimensional uterine ultrasound and a retrospective analysis of outcomes in relation with progesterone levels. The videos were also analyzed by a senior doctor, junior doctor, and a nurse for their reproducibility.

Setting: Instituto Bernabeu of Alicante is a private clinic.

Patient(s): The study included 197 consecutive patients undergoing in vitro fertilization (from 2018 to 2019) with a history of recurrent implantation failure (defined as unsuccessful implantation of a total number of ≥3 blastocysts originated from oocyte donation cycles). Because it is known that most failures are attributed to the quality of the embryo, we deemed it important to explore the potential uterine factors explaining the failures in oocyte donation cycles, the use of which decreases the probability of embryo-related factors influencing it.

Intervention(s): The participants were evaluated for uterine contractions and serum progesterone levels (10-30 minutes before the embryo transfer procedure). Uterine contractility (UC) was assessed by recording a 6-minute-long video using a 4D mode (Voluson E10; General Electric, Boston, MA), which was performed by a single operator (B.M.).

Main Outcomes Measure(s): The contractions were seen like waves going through the endometrial cavity. They were counted on a ×15 accelerated recording video. To define high-frequency UC, we separated uterine peristalsis (contractions per minute [cpm]) into quartiles. The highest quartile defined the hypercontractility group (>1.51 cpm; n = 41), considering the remaining quartiles as the normal contractility group (≤1.51 cpm; n = 156). The Mann-Whitney U test was performed. The intraclass correlation coefficient was used to validate variability. P <.05 was considered significant. SPSS version 21.0 was used for the statistical analysis. The institutional review board's approval was obtained.

Result(s): Overall, an average of 1.1 cpm was found in the study population. There were no differences between the groups (hypercontractility vs. normal contractility) in terms of patient age and the presence of any uterine factor (adenomyosis, myomas, adhesions, or polyps). An inverse association was observed between UC and progesterone levels. Low progesterone levels (15.9 vs. 19.5 ng/mL; P = .027) were observed in the HUP and NUP group, respectively. The intraclass correlation coefficient to evaluate the interobserver variability was 0.75 (0.63-0.85; P = .000).

Conclusion(s): Four-dimensional ultrasound assessment provides a dynamic view of uterine contractions, including their directionality and frequency. Even though recurrent implantation failure is yet a title of obscure definition and probably associated with multiple factors, a subgroup of patients with elevated UC associated with "low" progesterone levels may have a potential effect on their outcomes. Four-dimensional scan evaluation of UC constitutes a promising diagnostic tool in clinical practice; however, larger studies confirming our initial results are still pending.