Despite numerous developments in assisted reproduction, the implantation rate of the replaced embryos in IVF and ICSI remains low. In 1995, Edwards observed that despite the replacement of good quality embryos, 85 percent of these embryos do not implant (1). These low success rates have been variously blamed on compromised endometrial receptivity, compromised implantation capacity of the embryo, or a suboptimal embryo transfer (ET) technique. The aim of this review is to describe the technique of ET, to evaluate the various modifications proposed in order to maximize the chances of pregnancy, and to discuss the different approaches available for managing difficult ETs.

THE TECHNIQUE OF ET

ET is usually performed two to five days after oocyte retrieval. Although the knee-chest position was originally recommended by some authors, most of the transfers are now performed in the lithotomy position (2, 3). The procedure is performed under sterile conditions; the patient is draped, a speculum is inserted in the vagina, and the cervix exposed. The cervical mucus is aspirated using a mucus aspirator and the cervix is then cleansed with a swab soaked with saline or culture medium.

Different types of plastic catheters are used for ET varying in length, diameter, stiffness, and memory and are checked for embryo toxicity. Catheters are either preloaded or afterloaded, depending on whether embryos are loaded directly into the catheter or whether the outer sheath is first placed in the uterine cavity using a guide wire or obturator.