Traditionally, embryo transfer has been performed using tactile senses and judgment to determine when the transfer catheter is in the correct position, this being referred to as ‘clinical touch’. Alternatively, ultrasound imaging can be used to guide placement of the catheter during embryo transfer. Visualization of the catheter during insertion can help the operator to align it with the curvature of the uterus, to ensure the embryos are deposited in a favorable position within the endometrial cavity and to check the position of air bubbles after embryo transfer1 (Figure 1). Frequently, transabdominal ultrasound-guided embryo transfer (TA-UGET) is performed, and this requires the patient to have a full bladder. Less commonly, transvaginal ultrasound (TV-UGET) is performed, which requires the use of a special, extra-long, embryo transfer catheter along with either a special speculum that permits the ultrasound probe to be retained in the vagina while performing the transfer2 or removal of the vaginal speculum after insertion of the outer sheath of the catheter into the cervix, followed by insertion of the ultrasound probe into the vagina to adjust the catheter position under ultrasound guidance before performing the transfer3. Another possibility is evaluation of the cervix and uterus for planning catheter placement in advance; this can be accomplished by measuring the length from the external os to the fundus, either using a uterine sound or by ultrasound (Figure 1). This technique is called uterine-length measurement before embryo transfer (ULMbET). Large trials are required for the proper evaluation of patient-based outcomes in reproductive medicine because they can detect small, yet clinically relevant, differences. Revelli et al.4, in the current issue of the Journal, report a study in which they randomized almost 1700 women to compare the effectiveness of ULMbET by transvaginal ultrasound and TA-UGET, resulting in very similar reproductive outcomes (ongoing pregnancy rate = 32% vs 33% for ULMbET vs TA-UGET, intention-to-treat analysis). While this might not seem interesting at first, ULMbET has some advantages that are unrelated to the reproductive outcome. It simplifies fertility treatment, both improving the experience for the patient and reducing the costs involved: there is no need for the woman to have a full bladder, reducing the discomfort related to the embryo transfer procedure (1% vs 20% of the women complained of moderate to severe discomfort)4; and it eliminates the need for a second well-trained sonographer or physician to be present, reducing costs. Efforts towards making fertility treatment simpler and more affordable should be at the forefront in reproductive medicine research, because financial access is, along with safety, one of the most critical issues in this field. Although in-vitro fertilization (IVF) is effective, several cycles are frequently necessary to achieve a live birth5 and the expense makes it inaccessible to most women. This is particularly true in developing countries, in which even a single treatment might mean catastrophic expenditure for the couple6. Additionally, several couples give up before achieving pregnancy because of the physical and psychological burden, which could be reduced by using a friendlier and less uncomfortable approach7, 8. It is interesting to examine the evidence from the study of Revelli et al.4 alongside that from other randomized controlled trials comparing different ultrasound techniques for assisting embryo transfer9. Considering only studies that reported ongoing pregnancy, we identified 13 studies comparing TA-UGET with ‘clinical touch’10-22, three studies comparing TV-UGET with TA-UGET23-25 and only the present study comparing ULMbET with TA-UGET4, and compared them in a forest plot (Figure 2). As a result, we are confident that TA-UGET improves pregnancy rate compared with ‘clinical touch’ and that similar results might be obtained by using either TV-UGET or ULMbET. Additionally, two smaller RCTs, published only as abstracts and not reporting ongoing pregnancy, compared ULMbET by transvaginal ultrasound with TA-UGET26, 27. These studies also had encouraging results, with ULMbET proving to be at least as effective as TA-UGET: reported pregnancy rates were 10/13 (77%) vs 5/13 (38%)26 and 44/100 (44%) vs 25/100 (25%)27. In summary, assessing the ULMbET and performing embryo transfer with the patient's bladder empty has financial advantages, is less uncomfortable for the woman and provides similar results when compared to TA-UGET. It is likely, therefore, that this technique will be employed by several centers around the world in the near future.
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Jul 3, 2024
E Seli 
Open Access