The Microinjection Technique and the Role of the Acrosome Reaction in Microfertilization

Abstract

An increasing number of men with male factor infertility seek assistance for conception by in vitro fertilization (IVF) and related techniques such as gamete intrafallopian tube transfer (GIFT). However, there is little prospect of success for men who have semen of severely reduced quality with low numbers of morphologically normal sperm which have forward progressive motility. Although sperm with only a single or double defect of low sperm numbers, impaired motility or high morphological abnormality, have a reduced chance of fertilizing eggs (Yovich and Stanger, 1984), pregnancy rates following IVF in these cases are not usually reduced (Yates et al., 1988). In such cases superovulation yields a number of eggs which can be fertilized and several early embryos can usually be replaced in utero. Pregnancy rates in GIFT for couples where the husband has reduced semen quality is disappointingly low (Jansen, 1988) and it is preferable to inseminate eggs in vitro and transfer pronuclear ova or cleaving embryos to the wife’s oviduct or uterus. Three pregnancies have resulted in cases of severe oligoasthenozoospermia by the transfer of pronuclear ova into Fallopian tubes, after micro-insemination sperm transfer (MIST) under the zona (Ng et al., 1988,1989c). The majority of men who have male factor infertility have multiple sperm defects so that fertilization cannot be achieved by conventional insemination methods in vitro or in vivo. There are also some men with apparendy normal sperm who are incapable of fertilizing eggs in vitro because of some unknown problem in their fertilizing capacity or egg compatibility. This has led to research into ways of bypassing the zona pellucida which is the major barrier to sperm penetration of the oocyte.