The Research On Relationship Of Zona Pellucida Thickness/Hardness Of Human Embryos And Clinical Pregnancy Outcome Following In Vitro Fertilization Treatment And The Use Of Laser In Assisted Hatching

A low implantation potential of human embryos replaced in the uterus after in vitro fertilization (IVF) is a great barrier in assisted reproduction. Recently, failure of the embryonic zona pellucida to rupture following blastocyst expansion has been supposed as a possible contributing factor in implantation failure. And then an idea of creating a hole artificially in the zona pellucida, i.e., Assisted Hatching (AH) has been put forward in order to help blastocyst hatching. Some interest has been generated in studying the rationale for assisted hatching. Some reports suggest that embryos with lower zona pellucida thickness (ZPT) and higher zona pellucida thickness variation (ZPTV) had a better chance of successful hatching and so the patient become pregnant; another reports suggest that in vivo aging; in vitro culture and exposure to ultralow temperature may induce zona hardening and then impair the embryo ability of hatching. So for some special patients, zona drilling or local zona thinning with increased ZPTV may help embryo hatching. At the same time, different types of assisted hatching have been developed, such as mechanical tearing, chemical digesting and laser burning. However, the clinical relevance of assisted hatching remains elusive. The controversy focus on which type of patient could benefit from assisted hatching and which method of assisted hatching is more applicable. So far, due to the limit of research method and material, all these research are at the beginning stage, particularly that on zona hardening and laser thinning assisted hatching, there is no report in our country.The recent development of a non-contact 1.48 rn diode laser system offers an excellent method for the basic research of physical properties of zona pellucida as well as the clinical application of assisted hatching. Our research used this laser system and its precise measurement software to make a all-round study on the relationship of zona pellucida thickness / hardness variation of human embryos and clinical pregnancy outcome following in vitro fertilization treatment and the application of laser thinning in assisted hatching. The purpose of this study was to try to provide the basic rationale for assisted hatching and an alternative assisted hatching method.MaterialsAll the oocytes and embryos were recruited from Reproductive Medical Center in the First Affiliated Hospital of Zhengzhou University during a five-month period from April 2002 to August 2002. All couples included in this study gave written consent to experimentation on their excess or discarded oocytes or embryos.1. 246 embryos selected for transfer on day 3 with clear image record from 50 IVF cycles (153 embryos) and 31 Intracytoplasmic Sperm Injection (ICSI) cycles (93 embryos).2. 32 discarded unmutured oocytes on dayO, forty-two discarded unfertilized oocytes on day2 and 91 discarded unfertilized oocytes on day3 (dayO refers to the day of oocyte collection) from 53 ICSI cycles; 127 normal fertilized embryos from 62 IVF and 41 ICSI cycles with a grade of IH-IVand improper to freeze after day3 embryo transfer; 97 discarded embryos after day3 thawed-embryo transfer with a grade of III-IVfrom 39 cycles.3. 101 discarded fertilized embryos from 62 IVF and 41 ICSI cycles with a grade of II -III after day3 embryo transfer, assisted hatching group consisted of 50 embryos, control group consisted of 51 embryos.Methods1. The laser system measurement software is used to measure the ZTP of theembryo and the ZPTV were calculated;2. The laser system is used to confirm the correlation of laser energy and the size of the produced zona hole.3. The laser system is used to measure the minimum energy for effectively drilling the zona pellucida;4. The laser system is used to make a local thinner area in the zona pellucida, record the blastocyst formation, and hatching;5. The methods of IVF-ET refer to the routine ways in our center [1]. Results1. The clinical correlations of ZPT and ZPTV1.1 The ZPT and...