The Effect of Uterine Length Measurement before Embryo Transfer versus Transabdominal Ultrasound-Guided Embryo Transfer on FET Cycle Outcome: A Randomised Clinical Trial.

More than 40 years have passed since the first pregnancy after in vitro fertilisation (IVF). Despite significant progress in controlled ovarian stimulation, oocyte recovery, and fertilisation methods, the outcomes of embryo transfer (ET) remain almost the same ( 1 ). During the IVF cycles, more than two-thirds of the cases reach the ET stage. However, a large proportion of the cases fail to result in birth. This significant number of failures depends on embryo quality, endometrial receptivity, and the ET technique ( 2 ). ET is a critical process in IVF that is influenced by catheter type, operator experience, and site of embryo placement in the uterine cavity. Ultrasound-guided ET was first used in 1985 to minimise trauma to the endometrium and find the desired position for releasing the embryo ( 3 , 4 ). In several studies, ultrasound-guided ET has led to a higher clinical pregnancy rate compared to clinical touch ET (CTET) ( 5 , 6 ). A comparison of transvaginal ultrasound (TVS) for ET and transabdominal ultrasound-guided ET (TAUGET) had comparable results ( 7 ). However, using TVS during ET is an added burden for the doctor and uncomfortable for the patient due to the simultaneous usage of a speculum, vaginal probe, and transfer catheter ( 4 ). On the other hand, TAUGET requires an additional operator, a patient with a full bladder, and extra catheter movement to spot the catheter tip in an ultrasound image, which may cause damage to the endometrium ( 8 ). Various methods, such as uterine length measurement before ET (ULMbET) have been employed in recent years to overcome these disadvantages. In this method, uterocervical length is measured before the transfer, and the catheter is adjusted with respect to the measured length to ensure success of the transfer ( 9 , 10 ). Few studies have compared ultrasound-guided ET with ET based on ULMbET. Therefore, in this randomised clinical trial we intend to compare ULMbET and TAUGET, keeping in mind that ULMbET enables determination of catheter length and anatomical variations, such as antiflexion and retroflection, before the ET process.

A total of 260 women, aged 18-40 years and who were candidates for IVF/intracytoplasmic sperm injection (ICSI) using FET enrolled in this study. Figure 2 shows the study flow chart according to the Consolidated Standards of Reporting Trials (CONSORT) guidelines. Although 373 women were considered for this study, 107 women did not meet the inclusion criteria, and two subjects were excluded because they requested blastocyst ET. Therefore, 264 women were randomised on the day of ET. Four randomised women in ULMbET group did not receive the allocated method after randomisation. In three cases there was no suitable embryo for transfer after thawing and one woman refused to continue the treatment cycle. Finally, 128 women remained in the ULMbET group and 132 women in the TAUGET group. Table 1 shows the baseline and cycle characteristics of the two groups. Age, AMH, duration of infertility, cause of infertility, BMI, endometrial thickness, number of transferred embryos, and good quality embryos were comparable between the ULMbET and TAUGET groups (P>0.05). Flow chart of study based on CONSORT guidelines. ET; Embryo transfer, ULMbET; Uterine length measurement before embryo transfer, and TAGET; Transabdominal ultrasound-guided embryo transfer. Basic and cycle characteristics of the experimental and control groups * ; Age is presented as mean ± SD and compared by the Student’s t test, ** ; Mean ± SD, median and IQR, compared by the Mann-Whitney U test, *** ; Data are presented as percentage, and the differences between groups compared using the chi-square test, TAUGET; Transabdominal ultrasound-guided embryo transfer, ULMbET; Uterine length measurement before embryo transfer, BMI; Body mass index, AMH; AntiMüllerian hormone, PCOS; Polycystic ovary syndrome, and DOR; Diminished ovarian reserve. Assisted reproductive technology (ART) outcomes showed no statistically significant differences in chemical pregnancy rate (31.3 vs. 36.4%, P=0.384), clinical pregnancy rate (23.4 vs. 28%, P=0.397), and implantation rate (15 vs. 17.8%, P=0.401) between the ULMbET and TAUGET groups, respectively. The early miscarriage rate was also comparable between the two groups (P=0.555, Table 2 ). ART outcomes in the experimental and control groups Data are presented as percentages; the differences between groups are compared using the chi-square test. TAUGET; Transabdominal ultrasound-guided embryo transfer, ULMbET; Uterine length measurement before embryo transfer, and ART; Assisted reproductive technology.

Our results indicated that ULMbET is as effective as TAUGET in ART cycles and the pregnancy rate is comparable between these two ET methods. ET is the final step in ART cycles and is a critical procedure ( 2 ). According to an evidence-based guideline, an atraumatic ET is very important and highly recommended to achieve a reasonable live birth rate ( 12 ). Ultrasoundguided ET was introduced in 1985 to reduce trauma and deposition of the embryo in the proper place. It is believed that visualisation of the catheter passage through TAUGET is useful, especially in uterine abnormalities like leiomyoma ( 13 ). Since then, numerous studies have compared ultrasound-guided ET with CTET. The live birth rate was found to be higher in ultrasound-guided ET than CTET ( 5 , 14 ). In ultrasound-guided ET the optimal distance between the tip of the catheter and the uterine fundus was better adjusted, which led to embryo deposition at better sites ( 1 , 15 ). A 2015 meta-analysis of randomised clinical trials reported a higher live birth rate in patients who underwent ultrasound-guided ET in comparison with CTET; however, based on the higher cost of ultrasound-guided ET and patient discomfort due to the requirement of a full bladder, both methods were deemed acceptable ( 16 ). A Cochrane review evaluated 21 studies that assessed the effect of these ET methods on ART outcomes and concluded that the outcomes were better in ultrasound-guided ET compared with CTET ( 5 ). Likewise, another review showed superiority of the ultrasound-guided ET to CTET in terms of clinical outcomes ( 17 ). Other researchers have reported similar results ( 2 , 8 ). Some studies recommended mock transfer in terms of the decreased trauma during ET ( 13 , 18 ). However, according to convenience of ultrasound use, ultrasound-guided ET is more logical for mapping cervicouterine direction and length. After introducing TVS as a helpful method to improve ET outcomes, some studies compared TVS and TAUGET, with conflicting results ( 7 , 19 - 21 ). Most results highlighted the utility of both methods. With regard to ULMbET, a prospective cohort study showed a non-significant difference in the overall pregnancy rate, and clinical pregnancy and implantation rates between the two methods of ULMbET and blind ET ( 22 ). For the first time, Lambers and colleagues compared ART outcomes between this method and UGET. They found the same pregnancy and implantation rates following the measurement of uterocervical length before ET and UGET ( 23 ). A large randomised clinical trial, which was similar to the current study, showed comparable ART outcomes between ULMbET and TAUGET ( 10 ). A review article indicated that ultrasound-guided ET led to better results than CTET, and ULMbET had similar outcomes compared with UGET; however, since ULMbET takes less time and does not require a second technician, it was found to be easier than ultrasound-guided ET. Moreover, ULMbET reduces the full bladder sensation, which is a key factor in patient discomfort ( 4 ). In addition to the above-mentioned features of ULMbET, another reasonable aspect of this method is the use of the higher resolution TVS instead of transabdominal ultrasonography in obese women. Furthermore, the application of TVS during ET faces difficulty in the procedure for operators and women. Otherwise, during ULMbET, the use of a vaginal probe, in addition to uterocervical length measurement, provides more helpful information such as uterocervical angle and uterocervical anomalies. Then, a simple map for catheterisation and embryo deposition sites and a solution for the existing problems before ET would be available. For example, an operator can perform ET with a full or empty bladder in a situation like anteversion or retroversion of the uterus. In addition, the opportunity that ULMbET could be done simultaneously with TVS for endometrial thickness measurement makes this method more cost beneficial. The main limitation of our study was that the patients and operators were aware of the study procedure assignment. The second limitation was that patient follow-up did not include live birth.

Our study showed that although the ART outcomes following ULMbET and TAUGET were the same, advantages of ULMbET that include better patient compliance and lack of a need for a second operator make this method superior to TAUGET.

We conducted this open-label randomised clinical trial at Yazd Reproductive Sciences Institute from December 2021 to September 2022. This study was conducted according to the Declaration of Helsinki and its subsequent amendments. The study protocol was approved by the Ethics Committee of the Yazd Reproductive Sciences Institute, Shahid Sadoughi University of Medical Sciences, Yazd, Iran (IR.SSU.RSI.REC.1399.047). This trial was also registered as (IRCT20110509006420N24) in the Iranian Registry of Clinical Trials. All couples who participated in this trial signed a written informed consent for study participation. Inclusion criteria consisted of infertile women between 18 and 40 years of age who were scheduled for frozenthawed ET (FET) cycles using cleavage-stage embryos. Women with the following conditions were excluded from the study: body mass index (BMI) >30; those whose partners were diagnosed with azoospermia; and those who have to undergo testicular sperm extraction or percutaneous epididymal sperm aspiration. The 264 eligible women who consented for study participation were randomly assigned in a 1:1 ratio into either the experimental group (ULMbET) or control group (TAUGET) group via permuted block randomisation. We took into consideration nine blocks of 32, which was generated by Random Software Allocation, version 1. The randomisation list was prepared by an independent statistician before recruitment. However, the group assignment was kept in sequentially numbered, opaque, sealed envelopes. The clinicians who performed the ET were not blinded to the patient assignment. For both groups, endometrial preparation was done using 6 mg oral oestradiol (Estradiol Valerate, Aburaihan Co., Iran) per day starting the third day of the cycle until the 13th day of the cycle. Endometrial thickness assessment was done on cycle day 13. When endometrial thickness reached ≥7 mm, all women received progesterone, Fertigest vaginal suppository, 400 mg twice daily plus a 50 mg intramuscular (IM) progesterone injection (Aburaihan Pharmaceutical Company, Iran). Uterocervical length measurement was performed for the ULMbET group simultaneously with endometrial thickness assessment by TVS. For this purpose, TVS was performed with a sagittal view and the distances between the top of the endometrial line and the internal os, and then from internal os to the external os were measured. At the time of ET, the length of the catheter was adjusted in accordance with the recorded measurements using an adjustable cervical stop on the catheter, so that the distance from the fundal endometrium to the embryo deposition site was considered equal to 1.5 cm ( Fig .1 ). For all women, cleavage-stage ET was done using CT after three days. Uterine length measurement before embryo transfer. For women in the TAUGET group, ET was done with the assistance of a second physician who performed the transabdominal ultrasound. The embryos were released when the tip of the catheter was observed at around 1.5 cm from the fundal endometrial surface. For both groups, the embryos were warmed on the day of transfer as previously described ( 11 ) and a maximum of two embryos were transferred using an ET catheter (PM Trans Set, Prince Medical, France). In order to avoid any bias related to the operator’s experience and skill, all ULMbET procedures as well as the ETs were performed by two experienced doctors using the same ultrasound machine (Phillips model Affiniti 70 W, The Netherlands) equipped with both transvaginal and transabdominal probes. Luteal phase support was continued until the eighth week of gestation in cases of clinical pregnancy. The primary outcome of this study was clinical pregnancy. Positive clinical pregnancy was interpreted as presence of a gestational sac visualised by ultrasound 2–3 weeks after a positive chemical pregnancy test. The other outcomes were chemical pregnancy, which was defined as peripheral blood beta-human chorionic gonadotropin (β-hCG) ≥50 IU/L, measured two weeks after ET; implantation rate which was described as the percentage of intrauterine gestational sacs divided by transferred embryos; and early abortion, which was described as miscarriage before the 12 th week of gestational age. A sample size of 130 cases in each arm was estimated to permit the detection of a 10% difference in clinical pregnancy rate, which was the primary outcome between the two groups with 80% power at 5% alpha level. Statistical analysis was using the Statistical Package for the Social sciences (SPSS) software program (version 18, Chicago, IL, USA). The normality of continuous variables was assessed by the Kolmogorov-Smirnov test. Age was compared between the two groups using the student’s t test. Anti-müllerian hormone (AMH), BMI, the number of embryos, the number of transferred embryos, and the duration of infertility were compared between the two groups by the Mann-Whitney U test. The chi-square test was used for the comparison of categorical variables. P<0.05 indicated statistical significance.