Standardization of Variable Conditions of Embryo Transfer Into the Uterine Cavity in the Procedure of Medically Assisted Procreation in Humans

This study is a prospective, randomized, controlled, single-center clinical investigation designed to evaluate whether harmonizing embryo culture, embryo selection, and embryo transfer conditions improves pregnancy outcomes in patients undergoing frozen embryo transfer (CRIO-ET). While major advances have been achieved in embryo culture, monitoring, and selection, the embryo transfer procedure itself remains one of the least standardized steps in assisted reproductive treatment. During embryo transfer, embryos may be exposed to short-term variations in temperature, mechanical forces, and procedural timing, as well as operator-dependent differences in catheter handling and embryo expulsion. These factors may influence embryo viability and implantation potential. This study investigates whether the use of dedicated transfer-support devices can reduce procedural variability and provide a more controlled and reproducible transfer environment.

The study is conducted at a single specialized fertility center with extensive experience in IVF and ICSI treatment. All embryos included in the study are generated using standard IVF or ICSI procedures and cultured in a time-lapse monitoring system, allowing continuous assessment of embryo development. Embryo selection for transfer is supported by artificial intelligence-based grading software, providing objective and uniform evaluation across all participants and minimizing subjective variation. Only embryos meeting predefined quality criteria are selected for warming and transfer, ensuring standardization independent of the intervention arm. Embryos are cryopreserved at the blastocyst stage and subsequently warmed for transfer according to standardized laboratory protocols. All participants receive standard luteal phase support according to clinic protocol, typically including vaginal or intramuscular progesterone, starting on the day of embryo warming/transfer and continuing until pregnancy testing.

Participants who meet all inclusion criteria are randomized in a 1:1:1:1 ratio on the day of CRIO-ET to one of four study groups: a control group undergoing conventional manual embryo transfer, and three intervention groups in which embryo transfer is supported by dedicated devices designed to standardize specific procedural elements. Randomization is performed by independent administrative staff using sealed envelopes containing predefined codes. Participants and outcome assessors are blinded to group allocation, while physicians, embryologists, and nurses performing the transfer are aware of the assignment but instructed to maintain confidentiality. Statistical analyses are conducted by blinded statisticians until completion of primary analyses.

Endometrial preparation for frozen embryo transfer is carried out using either a natural ovulatory cycle or a letrozole-induced cycle, followed by luteal phase progesterone supplementation according to routine clinical practice. Ovulation is confirmed using ultrasound monitoring, hormonal assessment, or administration of human chorionic gonadotropin (hCG). Embryo transfer is scheduled for the fifth day after ovulation. Decisions regarding continuation or discontinuation of progesterone supplementation after transfer follow standard clinical guidelines.

All embryo transfer procedures are performed under ultrasound guidance using soft embryo transfer catheters. In the control group, embryo loading and transfer are conducted manually following routine practice. In the intervention groups, transfer is supported by one or both of the following devices: Embryocase, a thermally insulated case designed to stabilize environmental conditions during transport of the embryo-loaded catheter, and Embryopass, an electronically controlled applicator that standardizes precise embryo aspiration and expulsion speed, optimal fluid volume, programmed injection time, eliminates pressure fluctuations and plunger backflow, prevents embryo re-aspiration and detects transfer catherer oclusion. Embryo loading follows a predefined sequence, and the duration is recorded. In groups using Embryopass, embryo loading and expulsion is performed according to device instructions, ensuring reproducible, operator-independent transfer. After transfer, the catheter is examined microscopically to confirm complete embryo release. Repeat transfer is permitted if necessary according to routine practice. Patients leave the procedure room immediately after transfer without post-procedure immobilization.

Procedural data related to embryo warming, loading, transfer conditions, and any deviations from the planned procedure are recorded in an electronic case report form (eCRF). Study data are collected and managed in compliance with applicable data protection regulations. Safety monitoring includes systematic collection of adverse events (AEs) and serious adverse events (SAEs). Emergency unblinding for an individual participant is permitted if clinically indicated, particularly in the event of an AE or SAE potentially related to the investigational devices.

The study's primary endpoints are biochemical pregnancy (serum β-hCG ≥5.3 mIU/ml measured 10-15 days after transfer) and clinical pregnancy (presence of a gestational sac on transvaginal ultrasound 25-35 days after transfer). Secondary endpoints include implantation rate, live birth rate, device-related adverse events, and usability scores from embryologists and physicians. Usability assessments capture ease of use, workflow integration, and overall satisfaction with the devices.

Pregnancy assessment includes biochemical pregnancy testing followed by confirmation of clinical pregnancy by ultrasound. Participants may continue pregnancy follow-up either at the study center or at another medical facility, provided relevant medical documentation is available to the investigators. Information on pregnancy outcomes, including delivery, pregnancy loss, or ectopic pregnancy, is collected using a structured questionnaire until the end of pregnancy.

Statistical analyses include chi-square tests for categorical outcomes (pregnancy and implantation rates) and t-tests for continuous variables (e.g., embryo loading time or device-related procedural metrics). Statistical significance is defined as p < 0.05. The sample size of 160 participants provides 80% power to detect a 15% absolute increase in clinical pregnancy rate in the combined device arm compared with the control arm. Analyses are conducted on an intention-to-treat basis, with sensitivity analyses performed to evaluate robustness.

Data management complies with the General Data Protection Regulation and local ethics committee requirements. All participant data are de-identified and stored securely. Only authorized study personnel have access, and standard confidentiality procedures are maintained. The study received approval from the institutional ethics board prior to initiation, and all participants provide written informed consent.

The EFECT study is expected to provide important evidence regarding the impact of procedural standardization on embryo transfer outcomes. By evaluating the combined effects of AI-supported embryo selection, elimination of human factor (embryologist and physician), controlled embryo loading and expulsion, as well as temperature stabilization, the study aims to determine whether these innovations can meaningfully improve pregnancy rates in medically assisted reproduction. If successful, the findings may support broader adoption of standardized embryo transfer protocols and device-assisted techniques in fertility clinics, potentially improving outcomes for patients undergoing frozen embryo transfer.