MALE FEMALE SEX-RATIO IN BIRTHS RESULTING FROM IVF ACCORDING TO SWIM-UP VERSUS PERCOLL PREPARATION OF INSEMINATED SPERM/

Two centers have independently reported a higher rate of male to femal e births following insemination of sperm prepared by a modified swim-u p technique. The principle of the modified swim-up is that a small per centage of the x-bearing sperm are the fastest and travel to the top o f the supernatant, followed by the y-bearing sperm; the bulk of the x- bearing sperm remain in the pellet. In this technique, the very top la yer is discarded and the resulting supematant is collected, leaving on ly the pellet. In contrast, with the conventional swim-up technique, t he entire supematant is collected. The study presented herein retrospe ctively evaluated the male to female sex ratio of births from in vitro fertilization using standard swim-up technique and compared these res ults to the ratio obtained from separating with Percoll. There were 53 % male births with swim-up vs. 54% with Percoll in singleton pregnanci es and 51% males with swim-up vs. 40% with Percoll with multiple birth s. Thus, conventional swim-up alone does not increase percentage of ma le births.