Trials for Improvement of Blastocyst Stage Transfer Technique

Recently the blastocyst stage transfer (BST) has been applied with several kinds of sequential media and good results have been achieved. The technique made it possible to select embryo potential for implantation and to prevent multiple pregnancies, especially triplets. Several reports [1] have been published on the efficacy of BST. One paper reported an improved pregnancy rate compared with Day 3 transfer and another [2] reported a very high conception rate and statistically better results than Day 2/3 transfer in cases of recurrent failure and aged women [3]. Several studies have described, however, the rate of conception to be app rox ima te l y equa l c ompared t o t ha t o f the conventional method [4, 5]. It would be therefore important to choose cases to apply BST to, such as recurrent unsuccessful or aged cases. Since BST has been developed, most IVF centers have adopted the technique, but there would be more room to improve the clinical results. In the present study, the choice of the medium in BST was discussed. And the efficacy of the two-step embryo transfer method that is one of the techniques developed to apply BST was estimated.