***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 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 Purpose The aim of this study was to determine if the size of zona pellucida thinning area by laser assisted hatching could affect the rates of pregnancy and implantation for vitrified-warmed embryo transfers at the cleavage-stage . Methods A total of 120 vitrified-warmed cleavage-stage embryo transfers were r and omly assigned to either quarter or half of zona pellucida thinning group . Results The rates of clinical pregnancy ( 46.7 versus 25.0 % ) and implantation ( 32.0 versus 16.2 % ) were significantly greater in the half thinning group than in the quarter thinning group ( P = 0.0218 and P = 0.0090 , respectively ) . Conclusions The results of this investigation show that , in vitrified-warmed embryo transfers at the cleavage-stage , the size of zona pellucida thinning area by laser assisted hatching impacts the rate of clinical pregnancy and implantation and that half of zona pellucida thinning significantly increases both of these results compared with quarter of zona pellucida thinning 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 To evaluate the overall effect of assisted hatching ( AH ) on the implantation , pregnancy , and live birth rates in women undergoing intracytoplasmic sperm injection ( ICSI ) cycles ; and to determine the effect of AH on the cytogenetic outcome ( chromosomal constitution ) of pregnancy . DESIGN Prospect i ve , r and omized study . SETTING Academic research environment . PATIENT(S ) A total of 172 couples were enrolled in the study . INTERVENTION(S ) Assisted hatching was carried out on day-3 ICSI embryos . MAIN OUTCOME MEASURE(S ) Implantation , clinical pregnancy , and live birth rates ; cytogenetic analysis of abortuses and umbilical cord blood sample s from newborns . RESULT ( S ) Biochemical , clinical , and ongoing pregnancy rates were not significantly different between the AH and control groups . The implantation rate was higher in the AH group than in the control group ( 16 % vs. 8 % ) , especially in women aged > or = 35 years . Postnatal umbilical cord blood sample s were collected and cytogenetically analyzed from 39 live births ( 20 from the AH group , 19 from the control group ) . Two abnormal karyotypes were found ( one AH , one control ) . There were seven spontaneous losses during the study interval . Six of the abortuses underwent cytogenetic study ( five AH , one control ) , and four were found to have an abnormal karyotype ( three AH , one control ) . CONCLUSION We found that AH improves implantation rates of ICSI cycles and seems to be most effective in women aged > or = 35 years . A larger sample size is needed to determine whether AH improves the take-home-baby rate .  Assisted hatching did not affect the rate of chromosomal abnormalities in live births in this study 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 
    Output:
    
This up date has demonstrated that whilst assisted hatching ( AH ) does appear to offer a significantly increased chance of achieving a clinical pregnancy , the extent to which it may do so only just reaches statistical significance .
The ' take home ' baby rate was still not proven to be increased by AH .
The included trials provided insufficient data to investigate the impact of AH on several important outcomes .
Most trials still failed to report on live birth rates