[Consequences of oocyte dysmorphy on the fertilization rate and embryo development after intracytoplasmic sperm...

This prospective study aimed to evaluate the impact of oocyte dysmorphy on the fertilization rate and embryonic development rate in an ICSI programme.

Three hundred and two couples have been included during 302 ICSI cycles, and 1970 oocytes have been studied in 4 ART centres. After decoronisation, 18 morphological criteria, including the size and shape of the oocyte, the thickness of the zona pellucida, the presence or not of debris in the perivitelline space, as well as the appearance of the cytoplasm and polar body have been noted.

In total 61.3% of the oocytes presented a dysmorphy, involving, almost equally, the different oocyte compartments. Among the dysmorphic oocytes, half presented more than one anomaly. On average, 9.2% of the oocytes were lysed the day after the micro-injection. The oocytes presenting an enlarged perivitelline space, or multiple vacuoles had a significantly raised lyse rate, 16.3% and 27.8%, respectively. The day after micro-injection, 61.3% of the intact oocytes were fertilized. The rate of fertilization was correlated to the number of abnormalities per oocyte: 1 anomaly: 64.6%, > or = 3 anomalies: 54.6%. The oocytes presenting a large perivitelline space had a slightly lowered fertilization rate (53.4%). On the other hand, those showing a cytoplasm containing refractile bodies had a slightly raised fertilization rate (68.6%). We did not see any statistically significant difference between the different types of oocytes concerning embryonic development at d2.

These results confirm and contribute new elements with respect to previously published data, showing that (i) oocyte morphology little affects fertilization and the first stages of embryonic development; (ii) certain dysmorphies, (enlargement of the perivitelline space) are specifically deleterious at certain stages in the process (lowering the fertilization rate); (iii) certain morphological differences (the presence of refringent bodies) are not anomalies, but can reflect physiological cellular changes.