[Fertilization of human ova in capillary tubes with a very small number of spermatozoa. A new treatment possibility in severe oligospermia?].

In contrast to the in vivo situation the current in vitro fertilization techniques require large numbers of spermatozoa per oocyte to achieve successful fertilization. In this study a culture system was developed in which successful fertilization was performed in haematocrit capillary tubes (75 mm length, 0.8-0.9 mm inner diameter) even if only low numbers of spermatozoa were used. Oocytes were fertilized in 5-10 microliters of different sperm suspension containing a total number of 500, 1000, 2000 and 4000 spermatozoa per oocyte (0.1-0.4 X 10(6) sperms/ml). In 10 patients participating in an in vitro fertilization programme 32 oocytes were fertilized in capillary tubes and 32 oocytes were cultured using standard methods (1 ml culture medium in tissue culture tubes, 0.1-0.2 X 10(6) spermatozoa/ml). The overall fertilization rate of oocytes cultured in tissue culture tubes was 78% (25/32) and the fertilization rates in capillary tubes using 4000, 2000, 1000 or 500 spermatozoa per oocyte were: 71% (5/7), 86% (6/7), 60% (6/10) and 50% (4/8), respectively. The fertilization rate of mature oocytes was higher compared to immature oocytes when fertilization was performed in culture tubes (83% and 63%) or in capillary tubes (74% and 44%). Fertilization in capillary tubes using a volume of the sperm oocyte suspension of 10 microliters compared to 5 microliters seems to provide better culture conditions resulting in higher fertilization and cleavage rates (75 and 91% versus 62.5 and 60%). These preliminary results indicate that fertilization of human oocytes under in vitro conditions can be achieved even with very low numbers of spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)