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FIGURE 3
Comparison of pregnancy rates with the use of soft and firm embryo transfer catheters. ASRM. Embryo transfer guideline. Fertil Steril 2017.
alternately assigned to either the Edwards-Wallace catheter (H.G. Wallace Ltd.) or the rigid metal Erlangen catheter (not a true randomization), the rigid system showed higher preg- nancy rates (19% Wallace vs 30% Erlangen, [recalculated] P1⁄4.0381) (77). In this study, the transfer technique was also different depending on the catheter system used. The combi- nation of a non-randomization system, the variable use of a cervical tenaculum, and the lack of ultrasound guidance may account for the lack of benefit seen with the Edwards- Wallace catheter. Three meta-analyses (44, 79, 80) comparing soft vs ‘‘hard’’ or ‘‘firm’’ catheters were excluded from this analysis, because the authors of these studies categorized the Rocket EmbryonÒ, TDT, and Labotect catheters, with soft inner and firm outer components, as firm catheters.
The majority of the literature, including 10 RCTs and 1 cohort study, shows no difference in IVF outcomes (clinical pregnancy rate, pregnancy rate, implantation rate) when comparing different types of soft catheters (81–91). A single RCT and one cohort study favored the Edwards-Wallace cath- eter compared with rigid catheters when looking at pregnancy rate (92, 93). None of the trials included demonstrated a difference in birth rates when comparing soft catheters to one another. The totality of the data strongly supports similar pregnancy rates and, in some studies, implantation rates when comparing transfers using a variety of soft catheters.
It appears that no soft embryo transfer catheter is clearly superior and that commercially available soft catheters perform similarly. Personal choice and cost can guide differ- ential use of one soft catheter over the other.
Summary statement:
There is good evidence to recommend the use of a soft embryo transfer catheter to improve IVF-embryo trans- fer pregnancy rates. (Grade A). Data on live-birth rates and specific types of soft catheters are limited.
Does Positioning the Catheter at the Time of Embryo Transfer Affect IVF-Embryo Transfer Implantation, Pregnancy, and Live-birth Rates?
In terms of embryo transfer technique, it is widely accepted that avoiding touching the uterine fundus is one of the
most important factors leading to a successful transfer. How- ever, what is unclear is the ideal location for embryo place- ment within the uterine cavity. Four RCTs were designed to answer this question (94–97). One RCT examined three different placement locations (1.0, 1.5, and 2.0 cm) from the uterine fundus (94). It found statistically significantly (P<.05) higher implantation rates for placement between 1.5 cm and 2.0 cm compared with 1.0 cm, and statistically significantly higher (P<.05) pregnancy rates when the selected location was approximately 2 cm from the uterine fundus compared with 1 cm from the fundus (94). When placement was compared between <1 cm and 1–1.5 cm, one randomized controlled study demonstrated improved pregnancy rates and implantation rates at the location farther from the fundus (97). Two additional randomized controlled studies found no difference in implantation rate and pregnancy rate, with one study dividing placement into the upper vs lower half of the endometrial cavity (95) and the other comparing 2 cm from the fundus vs the uterine cavity midpoint (96). Five cohort studies (98–102) assessing the influence of embryo placement produced mixed results. Only one of those studies found no impact on pregnancy outcome based on embryo placement position (98). However, it was the oldest of the studies, reported in 1996.
The majority of the studies found that embryo placement impacted pregnancy rates, with pregnancy rates highest when the embryo was placed in the upper or middle area of the uter- ine cavity, at least 1 cm away from the fundus (94, 96, 97, 99– 102). A 2015 RCT that demonstrated no difference when the catheter tip was 2 cm from the fundus or in the middle third of the uterine cavity further supports placement in the upper or middle uterine cavity for embryo expulsion (96). One difficulty when comparing studies examining optimal embryo placement is the lack of consistency in comparative placements, with some studies assessing exact distances from the fundus, and others dividing the uterine cavity into areas.
Finally, the placement of the outer catheter may also affect pregnancy rates. In a cohort study of 408 patients who underwent embryo transfer, overall pregnancy rates were significantly better in those patients (n1⁄4218) for whom the outer sheath did not go beyond the internal os compared with patients (n1⁄4190) for whom the catheter was
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