Influence of catheter, syringe and inclusion of air-fluid columns on the release of embryos in a continuous media in vitro model

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The aim of the study was to assess the embryo release dynamics from the embryo transfer (ET) catheter contributed by the catheter components (syringe and cannula), as well as, the use of air-fluid columns and positioning of embryos within the catheter. The variables under consideration were: syringe and catheter configurations, and the location of the loaded embryos within the air-fluid or fluid alone columns. The specifications are described as follows: 1) three 1.0 cc syringes of different plunger design configurations (Becton-Dickinson (BD)=flat, Terumo=conical and Norm-Ject (HSW)=piston-like); 2) three catheters (Frydman 4.5 cm, Frydman-short and Wallace) and; 3) seven types of loading the catheters consisting of incorporating air-fluid or fluid alone and embryo placement within the columns. The air/fluid and embryo positioning combinations (beginning from the tip of the catheter) were: Type A (5 μl fluid/2.5 μl air/5 μl fluid + embryos/2.5 μl air); Type B-D (2.5 μl air/12.5 μl fluid + embryos); and Type E-G (15 μl fluid). Embryos were loaded within the first third of the fluid column in Type B and E; Type C and F embryos were loaded within the second third of the fluid column; and Type D and G embryos were loaded within the last third of the fluid column. In total, 63 combinations were tested and replicated 6 times. The loaded catheter was placed at a specific reference point in a 60 × 15 mm (marked at 0.5 cm intervals on the bottom) culture dish filled with 10 ml of media. The release and dispersion patterns of the embryos and the distance traveled from the tip of the catheter of each embryo was recorded. Syringe and loading type were the most significant variables affecting embryo release and distance traveled. Placing embryos at the first third of the fluid column resulted in the highest distance traveled regardless of the syringe or catheter. When assessing the effects of independent variables alone, it was realized that the most significant effect on embryo release distance was contributed by type of syringe (Norm-Ject>Terumo>BD). No significant differences were observed by comparing the different types of catheters. The findings of this study suggest that the type of syringe and positioning of embryos within the fluid column in the catheter may have a significant effect on the speed of embryo release. Syringes with a conical or piston-like plunger provide less control for the release of embryos resulting in the abrupt propelling of embryos, which could result in damage due to a ricochet/compression effect. Dispersion patterns resulting in embryos released in different directions were also noted for the syringes described above, and especially when air was introduced in the catheter. The incorporation of air may also result in entrapment of embryos after release from the catheter. Our findings suggest the use of syringes with a flat plunger, no air in the catheter, and positioning of the embryos within the proximal or middle of the fluid column in reference to the tip of the catheter.