Purpose We evaluated the relationship between meiotic spindle characteristics and in vitro fertilization cycle outcome. Methods Five hundred sixty-nine oocytes from 86 in vitro fertilization cycles were analyzed for fertilization and subsequent implantation rates. Oocytes were assessed for maturation status. The oocytes and embryos were cultured in sequential and nonsequential media (G Series, Vitrolife, Sweden) and incubated in 6% CO 2 , 5% O 2 at 37°C.Two hours following oocyte decumulation (38-39 h posthCG/GnRH administration) and prior to microinjection, the structure of the meiotic spindle was assessed using the Oosight Imaging System (CRI, UK). Results Four hundred fifty-six oocytes (80.5%) had a visible meiotic spindle, 82 (14.7%) had no meiotic spindle, and 31 (5.5%) were in telophase I. Oocytes exhibiting a meiotic spindle had a significantly higher fertilization rate and a lower rate of abnormal fertilization. Implantation data were obtained for 195 of the embryos transferred. The implantation rate for embryos derived from oocytes with a meiotic spindle was 32.9%, while in embryos originating from oocytes without a meiotic spindle and oocytes in telophase, this value dropped significantly (8.8 and 0%, respectively). To determine the correlation between retardance values and implantation rate for each oocyte, we established four groups, finding a range of retardance values with significantly higher implantation rates (27.5, 21, 29.3, and 53.8%, respectively). Conclusion Meiotic spindle imaging may be a valuable tool for prediction of oocyte quality, and retardance values of meiotic spindles, together with classical morphological classification, can be useful to select embryos with a higher implantation potential.

Our results indicate that the effective window of time for insemination by ICSI might be wider than previously thought. It therefore appears that, within appropriate time frames, the management of ICSI cycles involving oocytes from young women in embryology laboratories could be adjusted to accommodate caseloads and workflow with no loss of oocyte viability or cycle efficiency.

Objetivo. Analizar varias características del embrión transferible, así cómo algunas características de las receptoras sobre las tasas de preñez. Materiales y métodos. Se evaluaron ciento setenta y cuatro transferencias en dos haciendas en Colombia. Las variables analizadas en las receptoras fueron los niveles de progesterona sérica, tamaño del cuerpo lúteo y el grupo genético. Las variables analizadas en los embriones fueron estadío de desarrollo, calidad y transferencia en fresco o congelado. Resultados. Ninguna de las variables individualmente predicen la tasa de preñez, sin embargo, existe la probabilidad de un mejor resultado cuando se usa un embrión excelente congelado (OD=5.100), bueno fresco (OD= 4.180) y si la receptora es ¾ Angus (OD=2.945). Conclusiones. La tasa de preñez sigue siendo un evento regulado de manera multifactorial y ninguno de los parámetros evaluados individualmente son responsables del éxito reproductivo.