Round spermatid injection (ROSI) is a technique of assisted reproduction whereby a round spermatid is injected into oocyte cytoplasm in order to achieve fertilization. This technique can be used to enable genetic fatherhood to some men who have no spermatozoa in the ejaculate (azoospermia) and in whom spermatozoa cannot be obtained surgically from the testicles. This condition is called non-obstructive or secretory azoospermia, as opposed to obstructive azoospermia, in which complete sperm production does occur in the testicles, and potentially fertilizing spermatozoa can be obtained by testicular sperm extraction (TESE) and used for ICSI. In cases of nonobstructive (secretory) azoospermia, on the other hand, testicular sperm production is blocked at different stages of the process of sperm formation (spermatogenesis). In those men in whom spermatogenesis is blocked at the stage of round spermatids, in which meiosis has already been completed, these round cells can successfully fertilize oocytes after being injected into their cytoplasm.
RoUnd sperMaTId INjectiOn (rosI) Is a TecHniquE of assistED reproDucTIon WHereby a RounD sPermatid is INjected into oocyTe cYTopLAsm iN order to aChieve fERtiliZAtIoN. this tecHNiQue Can be USED to enabLe geNETiC FathERhOod tO SomE Men wHO HaVe no spErmaTOzoa In the ejacULatE (AzooSPErMia) and iN Whom SPermAtoZoa CAnnoT be obtaIned SurgiCaLly FrOM THe tesTicLes. THIS conditIoN is caLled nOn-obsTructIVE oR secREtory AZOOspErmia, aS opposed to obsTRucTIVe azoospermia, in Which compLete SpeRm prodUcTion dOeS OccUR in the Testicles, aNd pOtEntiaLlY fertilizing sPERmatoZoA cAn be obtaINed by testicULar SPerm exTractIon (tEse) and uSeD fOR icsi. In cases of NONObstruCtive (seCreTory) azoOspErmIa, oN the OtHer hAnD, testIcuLar spErm pRoduCTion is BLockEd AT different stagEs of tHe prOCeSs Of sPeRM foRmaTIOn (sPermatogenEsIs). in thOse men IN wHom spermAtogeNesis is bloCked aT thE stage OF rOunD spermAtiDs, iN whICh meiosis has aLready BEen coMpLeTEd, tHEsE roUnd celLS Can sUccesSfuLly fertilIZE oOcytEs after Being injecteD InTo tHeir CYtoplasm.