General Considerations
The goal of embryo transfer (ET) is their placement in the uterus with minimal trauma to the endometrium and embryos.
The essential features of ET in human females remain unchanged since the first description by Robert Edwards nearly 30 years ago. Traditionally, scant attention has been focused on the technique of ET, which is often viewed as an unimportant variable in the success of an IVF cycle, and clinicians are often reluctant to change their habits or methods regarding this procedure.
In 1982, Leeton and his group described the technique for ET. They compared the success rate while using "end-opening" and "side-opening" ET catheters. The use of end-opening catheters produces a slight advantage in pregnancy rate.
Many factors have been proposed to explain the disparity between embryonic development and pregnancy rates. Much of the inefficiency of embryo implantation may be applicable to the ET technique. Uterine contractions, expulsion of embryos, blood or mucus on the catheter tip, bacterial contamination of the catheter, and retained embryos have all been associated with problematic and unsuccessful ETs.
The goal of transcervical ET is to deliver embryos in a gentle, nontraumatic fashion, to the uterine fundus, a location where implantation is maximized. The avoidance of blood or mucus on the catheter tip, retained or expelled embryos, and the generation of uterine contractions is of utmost importance. The use of a precycle trial transfer, as well as ultrasound guidance and cervical lavage, and “soft” catheters appears to increase the chance of a successful outcome. Careful attention to the numerous details of the ET technique appears to be as important as the efforts of the embryologist in the laboratory.
Type of Catheter
Several types of catheters are available: stiff versus soft materials, end- and side-openings, the presence of an outer sheath, malleability, and quality of the materials and finish. Whereas stiff catheters and the use of a rigid outer sheath make catheter placement easier, they may result in more bleeding, trauma, mucus plugging, and stimulation of uterine contractions. The use of soft catheters that facilitated the tip in following the contour of the cervical and uterine access, and minimized trauma to the endometrium (Wallace catheter), was first described by Edwards and colleagues in 1984.
The change from the stiff catheter (Tomcat) to the soft catheter (Wallace catheter) has been associated with an improvement in pregnancy and implantation rates, as well as fewer catheters exhibiting blood, mucus, or retained embryos.
Loading the embryos
Considerable variation in the volume and constitution of the medium loaded in the catheter has been noted. Some clinicians prefer using fluid alone, or mixture of air and fluid in the catheter during transfer. A large volume (60 µL) of transfer media and a large air interface may result in expulsion of embryos into the cervix, on the speculum, or adhere to the exterior of the catheter.Removal of the air column can minimize such complications. Several studies have reported an increase in pregnancy and implantation rates after reducing the amount of air and the ??total transfer volume. Others reported high pregnancy rates using a continuous fluid column of 30 .µL in a Wallace catheter attached to a 1 cc airtight syringe. The embryos are loaded preferentially toward the tip of the embryo column closest to the catheter opening
Performing a trial ET prior to the actual procedure Performing a trial (mock or simulated) ET before the actual transfer has been suggested in an effort to increase pregnancy and implantation rates. Several studies have been published on this topic. However, only one of these was a randomized, controlled trial (RCT) in which the authors reported that the pregnancy and implantation rates were significantly higher in the simulated-transfer group compared to the conventional-transfer group.