Micro-assisted fertilization

Abstract

In couples who undergo routine in vitro fertilization (IVF), 17% experience significant problems with fertilization and many others are unable to have routine IVF because the quality of their semen is too poor. Often, the only options previously available to these couples were to use sperm donated by fertile men or to remain childless. Micromanipulative assisted fertilization techniques have improved the treatment of severe male factor infertility significantly and this paper provides a brief overview of the recent methodologies. Initially, techniques such as zona drilling and partial zona dissection, in which a hole or slit is placed in the zona pellucida, demonstrated that fertilization and pregnancies could be achieved with semen of very poor quality, but successes were sporadic. Later, subzonal injection of spermatozoa provided more consistent results with many units reporting pregnancies; however, relatively low rates of fertilization (14-34%) and high rates of polyspermy remained unresolved problems. The latest technique, the injection of a single spermatozoon into the oocyte cytoplasm, although technically difficult in animal models, proved to be highly successful in the human, restoring fertilization rates to those seen in routine IVF (65%) and producing good pregnancy rates from transferred embryos. Intracytoplasmic sperm injection has become the method of choice in the treatment of severe male factor infertility and preliminary data suggest that there is no increase in congenital abnormality among babies born after the transfer of injected oocytes.