***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Cryopreservation of embryos may lead to zona hardening that may compromise in vivo hatching and implantation following thawing and transfer . Assisted hatching ( AH ) has been advocated as a means of assisting the natural hatching process and enhancing implantation . METHODS The aim of this study was to assess in a prospect i ve r and omized manner the effect of laser-assisted hatching ( LAH ) on implantation as well as clinical and multiple pregnancy rates ( the primary outcome ) after the transfer of frozen-thawed embryos . All embryos were thawed the day before transfer , and LAH was performed the next day on embryos that cleaved . Control group consisted of embryos that were transferred without AH . RESULTS The performance of LAH significantly increased implantation ( 9.9 versus 20.1 % , P < 0.01 ) , clinical pregnancy ( 27.3 versus 40.9 , P < 0.05 ) and multiple pregnancy rates ( 16 versus 40.3 % , P < 0.07 ) . In the LAH group , significantly more excess embryos that were left in culture hatched in vitro . CONCLUSIONS LAH improves the outcome of frozen-thawed embryo transfer when performed before transfer on embryos that were allowed to cleave Abstract Purpose : The role of assisted hatching in good-prognosis IVF patients was evaluated in a prospect i ve , r and omized , controlled pilot study , which was followed by a retrospective observational series . Methods : After assisted hatching was proved successful in a mouse embryo study , 20 good-prognosis IVF patients were r and omly assigned to either assisted hatching ( 13 ) or no assisted hatching ( 7 ; the controls ) . Following this series , 27 good-prognosis IVF patients were retrospectively evaluated to determine the outcome with assisted hatching . Results : In the prospect i ve study , clinical pregnancies result ed from 3 ( 23 % ) of 13 patients in the hatching group , compared to 3 ( 43 % ) of 7 in the control group . Implantation rates were similar : 9.6 % in the hatching group and 10.7 % in the controls . In the retrospective series , the 11.1 % implantation rate with assisted hatching was significantly less than the 42.9 % implantation rate seen with traditional IVF . Conclusions : Implantation and pregnancy rates are high in young women undergoing traditional IVF . Assisted hatching is not beneficial in these patients While there is much information and discussion on  pregnancy failure after assisted reproductive technologies , less emphasis is placed on the failure to collect oocytes after apparently successful ovarian stimulation . This retrospective survey review ed 4973 treatment cycles in order to obtain information about the likelihood of this event . Overall 42 women ( 43 treatment cycles ) failed to have oocytes collected [ 0.86 % of treatments started and 0.92 % of women given human chorionic gonadotrophin ( HCG ) ] . However , in only six cases was this failure unexpected ( 0.1 % ) with no obvious potential clinical reason ( i.e. all six cases had : HCG administered ; more than two follicles > 15 mm in diameter ; oestradiol values > 2000 pmol/l ; < 38 years old ; normal body mass index ) . Indifference concerning uncommon events is fraught with peril , as although rare , the particular outcome may be devastating to the individual , both economically and psychologically . Eighteen of the 42 women did not return for on-going treatment suggesting increased contact by clinic staff may be required when oocyte retrieval is not achieved . These data suggest that the failure to collect oocytes after apparently successful ovarian stimulation is rare and r and om . The information has proved useful in allaying the fears of couples contemplating assisted reproductive technologies OBJECTIVE To develop a new approach to partial zona dissection of oocytes and embryos for facilitating preimplantation genetic sampling and assisted hatching . DESIGN Controlled clinical study . SETTING Preimplantation genetic diagnosis and IVF program , Reproductive Genetics Institute/IVF Illinois , Chicago , Illinois . PATIENT(S ) Three hundred forty patients undergoing IVF in whom preimplantation genetic diagnosis or assisted hatching was required . INTERVENTION(S ) Three-dimensional partial zona dissection and conventional partial zona dissection were performed , with the use of a simple microneedle , on embryos before preimplantation genetic sampling or on day 3 of embryo development before ET . MAIN OUTCOME MEASURE(S ) Pregnancy rate , implantation rate , and ease of preimplantation genetic sampling . RESULT ( S ) A pregnancy rate of 42 % and an embryo implantation rate of 17.6 % were obtained in the group in which three-dimensional partial zona dissection was performed , compared with a pregnancy rate of 33 % and an implantation rate of 14.7 % in the control group , which underwent conventional partial zona dissection . Preimplantation genetic sampling can be performed without distortion of the blastomere configuration in the embryo . CONCLUSION ( S ) Three-dimensional partial zona dissection is a safe and simple mechanical means of creating an opening sufficient for the atraumatic removal of material from oocytes and embryos for preimplantation genetic diagnosis and assisted hatching OBJECTIVE To assess the effect of augmenting IVF with assisted hatching in the treatment of patients with repeated IVF failures . DESIGN Prospect i ve r and omized study . SETTING Division of Reproductive Endocrinology and Infertility of National Taiwan University Hospital . PATIENT(S ) From July 1993 to February 1996 , 49 patients with repeatedly failed IVF were treated with assisted hatching and were compared with 51 control subjects without assisted hatching .  INTERVENTION(S ) Assisted hatching . MAIN OUTCOME MEASURE(S ) Pregnancy rate and implantation rate per embryo after IVF-ET or IVF-tubal ET ( TET ) were measured . RESULT ( S ) The pregnancy rate ( PR ) in the assisted hatching group was found to be 36.7 % compared with 19.6 % in the control group , but the difference was not significant . When only patients receiving IVF-ET were considered , it was observed that the PR was significantly higher in the assisted hatching group than the control group ( 42.4 % versus 16.1 % ) . With IVF-TET however , the PR was found to be similar in both assisted hatching and control groups ( 25.0 % and 25.0 % , respectively ) . The rate of embryonic implantation in the IVF-ET patients was 11.0 % , which was significantly higher than that of control embryos ( 3.7 % ) . CONCLUSION ( S ) These results implied that IVF-ET , combined with assisted hatching , may improve the PR and implantation rate in patients with repeated IVF failures , but the same was not true in the case of IVF-TET In two separate prospect ively r and omized trials , intracytoplasmic sperm injection ( ICSI ) cycles were studied in a controlled manner to monitor the effects of either bovine oviductal epithelial cell co-culture ( n = 119 ) or assisted hatching by zona drilling ( n = 100 ) . In the first study , immediately following ICSI , all eggs were placed directly either onto partial monolayers of bovine oviductal cells or into regular culture medium . Although the embryo developmental rate was apparently compromised in part by the presence of the co-culture cells , ultimately there were no significant differences in either the viable pregnancy rate ( 31.6 % co-culture versus 29.0 % control ) or the embryonic implantation rate ( 11.4 % co-culture versus 13.6 % control ) . Assisted hatching also had no significant impact on ICSI cycle outcome in terms of either the viable pregnancy rate ( 30.0 % assisted hatching versus 32.0 % control ) or the embryonic implantation rate ( 8.5 % assisted hatching versus 13.5 % control ) . However , in female patients aged > or = 35 years , assisted hatching appeared to convey a marginally significant benefit in terms of both the viable pregnancy rate ( 35.5 % assisted hatching versus 11.1 % control ) and the embryonic implantation rate ( 10.3 % assisted hatching versus 3.1 % control ) . It seems that the overall improvement of ICSI cycle outcome can not be achieved by the general application of either co-culture or assisted hatching . Nevertheless , it is possible that there remain specific patient groups that might benefit from selected use of either of these modalities BACKGROUND Assisted hatching ( AH ) in fresh embryo transfer ( ET ) cycles increases the implantation and pregnancy rates , especially in women with a poor prognosis , repeated implantation failures and in older women . Little information exists in the literature regarding the role of AH in frozen-thawed embryo transfer ( FET ) cycles . METHODS Embryos were cryopreserved at the cleavage stage . On the day of FET , 160 patients were r and omized according to a computer-generated r and omization list in sealed envelopes into the  AH group and the  control group . The patients and the clinicians were blinded to the group assigned . In the AH group , the outer half of the zona pellucida over a quarter of the diameter of zona was removed using a 1480 nm non-contact laser . RESULTS The two groups were comparable in terms of demographic characteristics , ovarian response of the stimulated cycle and quality of fresh and frozen-thawed embryos . No differences in implantation , pregnancy and multiple pregnancy rates were found between the two groups . There was a non-significant trend of a higher implantation rate in the AH group when the zona thickness was > or = 16 mm . CONCLUSION Laser AH did not improve the implantation rate of FET cycles and should not be performed routinely in all frozen-thawed embryos at the cleavage stage OBJECTIVE The aims of this study were to compare preimplantation embryo quality in intracytoplasmic sperm injection ( ICSI ) with st and ard IVF  and to examine the impact of age and number and quality of embryos transferred on implantation and pregnancy . DESIGN Retrospective , controlled clinical study . SETTING Academic tertiary center . PATIENT(S ) We examined 211 consecutive couples undergoing ICSI who were matched with 211 couples undergoing IVF therapy during the same time frame . INTERVENTION(S ) In vitro embryo culture . MAIN OUTCOME MEASURE(S ) Day 3 embryo quality as judged by the number of blastomeres and morphology scoring . RESULT ( S ) Patients undergoing ICSI  had a significantly reduced number of embryos with good morphology and cleavage compared with IVF cases . Nevertheless , pregnancy and abortion rates were similar when adjusted by age and number of embryos transferred . Average cleavage status and age were significant predictors of implantation . Women of advanced age had significantly lower embryo cleavage and implantation rates . CONCLUSION ( S ) [ 1 ] The cleaving status of day 3 embryos is a valuable , although limited , indicator of implantation outcome . [ 2 ] In vitro fertilization-derived embryos had better cleavage rates and morphology scores than ICSI-derived embryos ; however , the implantation potential was similar for both groups . [ 3 ] The age-related decline in implantation rate was associated with impaired embryo growth rates BACKGROUND Assisted hatching ( AH ) in fresh embryo transfer ( ET ) could be associated with increased implantation rates . However , very few prospect i ve r and omized studies have specifically addressed the issue of AH during frozen-thawed embryo transfers ( FET ) cycles , those that have reported controversial results . The aim of this study was to evaluate the benefit of an enzymatic zona pellucida treatment of frozen-thawed embryos before transfer . METHODS This was a prospect i ve study including 125 non-donor FET cycles from 125 infertile couples . FETs were r and omly allocated into AH group ( n = 61 , embryos pretreated with pronase 5 IU/ml for 1 min at 37 degrees C ) or control group ( n = 64 , untreated embryos ) .  Zona pellucida thickness was measured for each transferred embryo . The main outcome parameters were clinical pregnancy and implantation rates . RESULTS The two groups were comparable regarding mean women 's  age , duration and indications of infertility , IVF outcome after fresh ETs , numbers and quality of fresh and frozen embryos , frozen-thawed embryo survival rates and blastomeres survival indexes . Despite a statistically significant decrease of zona pellucida thickness after pronase treatment [ ( mean + /- SD ) 18.5 + /- 2.25 versus 14.5 + /- 2.75 microm ; P < 0.0001 ] , implantation ( 9.6 versus 9.2 % ) and clinical pregnancy rates ( 18.0 versus 17.2 % ) were not statistically different after FETs , with a similar mean number of embryos transferred between AH and control groups , respectively . CONCLUSION Within the constraints of our protocol , partial enzymatic digestion of zona pellucida by pronase was not related with any benefit of the FET outcome especially concerning the implantation ability of frozen-thawed embryos BACKGROUND It is conceivable that defective embryo hatching plays a part in the mechanisms involved in the decrease of embryo implantation rates 
    Output:
    
The included trials provided insufficient data to investigate the impact of assisted hatching on several important outcomes