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Loading of the ET Catheter
Loading of the ET catheter should start after cleaning the cervix of cervical mucus and performing the dummy or trial ET. According to the dummy ET, the suitable ET catheter is selected and flushed with tissue culture medium. After flushing, the ET catheter is filled with culture medium with an extra 10–15 mL in the attached syringe. The required embryos for ET are aspirated in another 10 mL medium and a final 10 mL medium is aspirated to move the embryos away from the catheter tip (Fig. 4). Using a continuous fluid column containing embryos near the tip is recommended. The quantity of fluid used for ET should be as small as possible to prevent the embryos from flowing out of the cervical canal or into the tubes . A large volume (60 mL) of transfer media and a large air bubble in the catheter may result in the expulsion of the embryos. Meldrum et al. demonstrated an improvement in the pregnancy rates after reducing the total transfer volume. A continuous fluid column of 30 mL is recommended. Air loaded into the transfer catheter to bracket the embryo-containing medium was a standard practice. Two prospective randomized studies were done to investigate the effect of the presence of air bubbles in the ET catheter on the outcome of IVF. The authors concluded that the presence of air bubbles has no negative effect on ET uccess.
In an experimental study using Methylene Blue dye, the presence of air bubbles did not significantly affect the rate of extrusion of the dye at the external cervical os. However, there is no definitive reason to support the
Figure 4 Loading of the embryo transfer catheter: (A) continuous fluid column of tissue culture media containing the embryos and (B) the media containing the embryos between two air brackets.
Retained Embryos
One of the problems of ET is finding retained embryos in the catheter after the procedure, which decreases the implantation rate. This problem occurs much more frequently after a difficult ET . However, the pregnancy rate was not compromised when the retained embryos were returned immediately. Embryos were significantly more likely to be retained when the transfer catheter was contaminated with mucus (17.8 vs. 3.3%) or blood (12 vs. 3.3%) .In a retrospective analysis of 1363 ET procedures, it was found that 3.9% of all transfers were complicated by finding retained embryos . The authors concluded that immediate transfer of embryos retained in the catheter following the initial transfer attempt did not have an adverse effect on pregnancy outcome. However, it has been shown previously that theapproach of immediately retransferring retained embryos does not solve the problem , and they suggested that ET should be repeated one day later.
Another possible cause for retained embryos is the position of the embryos in the catheter. Small volumes of less than 40 mL are preferable, but it is dvisable to aspirate approximately 15–20 mL of culture medium first, and then the embryos are aspirated second. This is to ensure enough media to push out the embryos. It is also important, once the injection is done, to keep the pressure on the plunger of the syringe until complete withdrawal of the catheter to avoid re-aspirating the embryos. Some syringes have the property to ‘‘recoil’’ that causes respiration of the embryos back in the catheter when the plunger is released . An important precaution to minimize retained embryos is a slow withdrawal of the catheter after ejecting the embryos. Rapid withdrawal may create negative pressure and result in the withdrawal of the embryos following the catheter. It was found by Leong et al. that withdrawal of the catheter about 1 cm and brisk injection avoided retrograde flow of the transfer media along the catheter by "capillary action."
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