TIMING OF OOCYTE ACTIVATION, PRONUCLEUS FORMATION AND CLEAVAGE IN HUMANS AFTER INTRACYTOPLASMIC SPERM INJECTION (ICSI) WITH TESTICULAR SPERMATOZOA AND AFTER ICSI OR IN-VITRO FERTILIZATION ON SIBLING OOCYTES WITH EJACULATED SPERMATOZOA

In the first study me evaluated 101 oocytes [2, 4, 6, 8, 16, 18 and 20 h after intracytoplasmic sperm injection (ICSI)] that had been microi njected with testicular spermatozoa. Of the 70 normally fertilized ooc ytes (69%) 30 (43%) had two pronuclei by 6 h after ICSI. Fifty-one (73 %) by 8 h, 69 (99%) by 16 h and four of them by 20 h cleaved to the 2- cell stage. In the second study 95 cumulus-corona-oocyte complexes (CC OC) were divided into two groups. Forty-seven CCOC were inseminated by conventional in-vitro fertilization (IVF) and 40 metaphase-II oocytes by ICSI. Oocytes were evaluated at 2, 4, 6 (only after ICSI), 8, 10, 12, 18, 20, 22, 24, 26, 28 and 30 h after both ICSI and IVF. After IVF , 35 oocytes mere fertilized normally (75%), four of which (11%) had t wo pronuclei by 8 h, 11 (31%) by to h, 27 (77%) by 12 h and 35 (100%) by 14 h. The first cleavages had occurred by 24 h after insemination ( four oocytes, 11%). After ICSI, 34 oocytes were fertilized normally (7 9%), 13 of which (38%) had two pronuclei by 6 h, 27 (79%) by 8 h and 3 2 (94%) by 10 h. Three oocytes cleaved by 20 h after microinjection (9 %) and 19 by 24 h (56%). Pronuclei developed asynchronously in six ooc ytes after ICSI (18%) as opposed to 16 oocytes after IVF (46%). The re sults of this study suggest that the timing of pronuclear formation is no different when a testicular spermatozoon is microinjected into the oocytes from when an ejaculated spermatozoon is injected. Secondly, p ronuclear development and first cleavage generally take place 4 h soon er after ICSI than after IVF. On the other hand, a higher proportion o f oocytes develop two pronuclei asynchronously after IVF than after IC SI.