[Polyploidy occurring during in-vitro fertilization of human oocytes: frequency and possible causes]

In an IVF-program a total of 585 oocytes (180 patients) was examined for the presence of pronuclei 16 to 20 hours after the addition of spermatozoa. The fertilization rate was 71% and in 58 (10%) of the fertilized oocytes three or more pronuclei, indicating a failure of the block to polyspermy with polyspermic fertilization, could be observed. The frequency of polyspermy was related to the maturity of the oocyte, determined according to morphological criteria. Immature oocytes showed a higher percentage of polyspermic fertilization (32%) compared to mature oocytes (6%). Preincubation of oocytes (0-1.5, 2-4, 5-8 hours) prior to the addition of spermatozoa increased the fertilization rate (67%, 70%, 83%, respectively). The polyspermy rate seemed to increase (13%, 14%, 19%). The observed frequency, however, was not significantly different between the various preincubation intervals. The polyspermy rate was affected by the number of spermatozoa used for in-vitro fertilization. Insemination with 0.5-0.8, 1.0 or 1.5 X 10(6) spermatozoa/oocyte resulted in a polyspermy rate of 6%, 20%, 32%, respectively. The appearance of polyspermic fertilization was not related to the age of the patient (20 to 45 years) nor to the method of ovarian stimulation (Clomiphene, hMG, Clomiphene/hMG). Because of the high incidence of polyspermy under in-vitro conditions it seems to be important to examine the oocytes in the pronuclear stage on a routine basis. Reduction of the number of spermatozoa used for in-vitro fertilization and the exact timing of insemination according to the maturity of the oocyte might reduce the occurrence of polyspermic fertilization.