Romanian Biotechnological Letters Vol. 15, No.3, 2010, Supplement Copyright © 2010 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER 13 Ultrastructural aspects of human immature oocytes Received for publication, March 5, 2010 Accepted, May 7, 2010 DELIA HUTANU 1 , CONSTANTIN CRĂCIUN 2 , MARIA CHECIU 1 , IACOB CHECIU 1 1 West University, Chemistry-Biology-Geography Faculty, Biology Departament Chemistry-Biology-Geography Faculty, Biology Department, 16 Pestalozzi Street, 300115 Timisoara 2 ”Babes-Bolyai” University of Cluj-Napoca, Faculty of Biology and Geology Babes Bolyai University, Electronic Microscopy Center, 5-7 Clinicilor Street, 400006 Cluj-Napoca Corresponding author: Delia Hutanu, phone 0040256 592622, fax: 0040256592620, e-mail adress delia.hutanu@cbg.uvt.ro Abstract In vitro fertilization, one of assisted reproduction`s technique is, for some couples, the only possibility to conceive a child. One of the main condition that must be fulfield in order to reach this goal is the quality of human oocytes. The ovarian stimulation protocols used have as an important goal the oocytes quality. The maturity grade of the oocytes is a good indicator of their quality.The mature oocytes are prefered for fertilization, because the immature oocytes do not fertilize.The main objective of this study is to characterize the immature oocyte, in order to explain why they do not fertilize. For this study were used human oocytes obtained from the couples who underwent infertility treatment at „Bega” Universitary Clinic of Obstetric and Gynecology Timisoara, IVF Department. The results obtained revealed new aspects of zona pellucida`s ultrastructure.These aspects can explain why the immature oocytes do not fertilize, compared with the mature oocytes. The conclusion which can be drawn is that in order to increase the pregnancy rate for the infertile couples which undergo IVF, the stimulation has to be made in such way that the number of immature oocytes obtained to be minimum. Keywords: in vitro fertilization, maturity grade, zona pellucida Introduction Even if it seems surprising, in human reproduction, naturally are more failures than succeses due to natural causes and exogenous influences. In vitro fertilization has a modest succes rate at the first glance (25-30%), but it still represents a way of solving infertility for a lot of couples. For the embryologist the main goal is to obtain high quality embryos, with high implantation potential (CHECIU & al.[1] Starting from this premise we considered that new investigations regarding oocytes ultrastructure, may bring new data about their quality. The observations we have made taking in account the bibliografic data availble and our own data led us to investigate the ultrastructure of human oocytes. At folicular punction, the oocytes can be: immature, mature and postmature RABE & all [2]. For fertilization are used mature oocytes, because the immature ones do not fertilize. Material and methods The biologic material was obtained after correct information of the patients about the objective of the study and risks involved and after we obtained written consent from each couple.The study was made between 2000 and 2009, and we used 280 immature oocytes during this period of time.