Fertilization of human oocytes by microinjection of a single spermatozoon under the zona pellucida.

The authors report a method of micromanipulation for the insertion of a single spermatozoon under the zona pellucida of human oocytes that results in a high rate of fertilization without damage to the oocyte. Spermatozoa were exposed to calcium-depleted medium containing strontium chloride for 20 to 24 hours before resuspension in medium containing calcium to induce capacitation. Single spermatozoa treated in this way were injected under the zona pellucida of morphologically mature oocytes and fertilization was confirmed by electron-microscopy. Five of seven oocytes manipulated within 9 hours of aspiration from the follicle and 3 of 12 oocytes manipulated 23 to 28 hours after recovery from the follicle fertilized. This technique has profound implications for the possible treatment of severe male infertility.