***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: OBJECTIVE To study and evaluate a sequential , extended embryo culture system . DESIGN Prospect i ve study . SETTING University-affiliated IVF clinic . PATIENT(S ) All couples who were treated between October 1997 and July 1998 . INTERVENTION(S ) A st and ard human tubal fluid plus 10 % serum substitute supplement ( SSS ) culture medium was used . The embryos were transferred to extended culture medium ( S2 or G2 ) on day 3 . MAIN OUTCOME MEASURE(S ) Blastocyst formation and implantation and pregnancy rates . RESULT ( S ) Forty percent of the 20 donated cryopreserved embryos progressed to the blastocyst stage by day 6 . Clinical ly , 7 ( 5.6 % ) of the 125 cycles did not result in a transfer . Blastocyst formation rates ranged from 33%-63 % in the five study groups . Implantation rates ranged from 15%-52 % and pregnancy rates ranged from 37%-75 % . CONCLUSION ( S ) Extended culture to day 5 or 6 results in acceptable blastocyst formation rates , implantation rates , and pregnancy rates The transfer of blastocysts has been associated with a very high implantation rate . However , not all embryos achieve the blastocyst stage . Our study was set up to demonstrate whether embryo morphology on day 3 predicts subsequent blastocyst formation . A prospect i ve study was carried out in 48 patients with a mean of 2.9 failed in-vitro fertilization ( IVF ) attempts . In this new cycle , the morphology of the embryos on day 3 was noted . After pre- selection of the embryos which would have been transferred on day 3 , all embryos were cultured individually and allowed to develop further until transfer on day 5 . The clinical pregnancy rate per transfer was 46 % , and the overall implantation rate was 24 % . When only blastocysts were transferred the pregnancy rate was 53 % with an implantation rate of 30 % . Thirty-nine per cent of all embryos reached the blastocyst stage on day 5 ; 47 % of class 1 and 2 embryos ( good quality ) in contrast to 21 % of class 3 and 4 embryos ( poor quality ) . Respectively 45 % of class 1 and 2 embryos and 69 % of class 3 and 4 embryos arrested in development or degenerated . Only 51 % of the embryos that were transferred on day 5 had been pre-selected for transfer on day 3 . In conclusion , it appears that the predictive value of embryo morphology on day 3 for subsequent blastocyst formation is limited Results of french multiple collaborative studies are reported to evaluate the possible benefits of coculture in human IVF program . Prospect i ve r and omized study of IVF with transfer on day two versus IVF with transfer on day 6 shows that coculture does not improve overall results but leads to a reduction of triple or quadruple pregnancies . When applied to patients with more than 4 failures of embryo transfers on day 2 , delayed transfer of blastocyst results in a high rate of clinical pregnancy ( 39 % ) . Transfers of frozen-thawed blastocysts result in 17.8 % ongoing pregnancies .  Coculture is also a powerful tool for underst and ing early embryo development : when fertilization arises from sperm with poor characteristics or from frozen sperm of donor , embryo development appears to be altered : in these situations , rate of normally developing embryo is reduced and early embryo development becomes independent of fertilization rate OBJECTIVE To analyze the birth weights and sex ratio of infants born after blastocyst transfer .  DESIGN Retrospective analysis . SETTING Three infertility clinics . PATIENT(S ) Patients admitted for IVF with blastocyst transfer .  INTERVENTION None . MAIN OUTCOME MEASURE(S ) Birth weights and sex ratio of infants born after blastocyst transfer .  RESULT ( S ) Statistically significantly more male infants were born after transfer of fresh blastocysts , either cocultured or cultured in sequential media . No specific differences in birth weight were observed between infants born after blastocyst transfer and those born after spontaneous conception . CONCLUSION ( S ) More male infants than female infants were born after blastocyst transfer when transfers were performed as soon as the blastocyst stage was reached and male embryos had a faster cleavage rate BACKGROUND The respective advantages of day 3 and day 5 embryo transfer are a matter of debate . Previous comparisons did not include pronuclear stage zygote scoring and cumulative success rates ( fresh and cryopreserved embryos ) . METHODS Patients were r and omized prospect ively for day 3 or day 5 embryo transfer .  Day 3 embryos were selected for transfer and cryopreservation by using combined evaluation at the pronuclear and cleavage stages . RESULTS There was no difference between day 3 and day 5 fresh embryo transfers as to the rates of pregnancy ( 58 versus 62 % ) , clinical pregnancy ( 56 versus 58 % ) , delivery ( 50 versus 48 % ) , implantation ( 35 versus 38 % ) and birth ( 33 versus 36 % ) rates . The corresponding values for cryopreserved embryo transfers were also similar . However , day 3 embryo transfer compared favourably with day 5 transfer when the pregnancy ( 90 versus 66 % ) , clinical pregnancy ( 85 versus 62 % ) and delivery ( 77 versus 52 % ) rates were calculated per oocyte recovery attempt . CONCLUSIONS With a selected population of good prognosis patients and our embryo selection criteria , the implantation potential of day 3 and day 5 embryos is equal . Per oocyte recovery attempt , day 3 transfer is more clinical ly efficient than day 5 transfer , but at least one transfer of cryopreserved embryos is necessary to manifest this superiority The effectiveness of blastocyst culture and transfer in human in-vitro fertilization ( IVF ) was evaluated in a prospect i ve r and omized trial in patients having a moderate to good response to gonadotrophin stimulation . Embryos were transferred either on day 3 after culture to around the 8-cell stage in Ham 's F-10 medium supplemented with fetal cord serum , or on day 5 after culture to the blastocyst stage in the sequential serum-free media G 1.2 and G 2.2 . The pregnancy rates after transfer on day 3 or day 5 were equivalent , 66 and 71 % respectively ; however , significantly more embryos were transferred on day 3 ( 3.7 ) than on day 5 ( 2.2 ) . The number of blastocysts transferred did not affect the implantation rate , and pregnancy rates when either two or three blastocysts were transferred were 68 and 87 % respectively . The implantation rate of the blastocysts ( 50.5 % fetal heart beat ) was significantly higher compared to the cleavage stage embryos transferred on day 3 ( 30.1 % ) . The percentage of blastocyst development was not affected by the number of 2-pronuclear embryos , or by maternal age . Irrespective of the number of blastocysts formed , pregnancy rates were similar . Furthermore , the pregnancy rate following blastocyst transfer in patients with 10 or more follicles at the time of human chorionic gonadotrophin administration was not affected by patient age . More than 60 % of patients having blastocyst culture and transfer had supernumerary embryos for cryopreservation . The establishment of a pregnancy following thaw and transfer confirmed the viability of cryopreserved blastocysts cultured in the absence of serum or co-culture . The ability to transfer just two blastocysts while maintaining high pregnancy rates will therefore help to eliminate high order multiple gestations and improve the overall efficiency of human IVF Transfer of embryos at the blastocyst stage has been associated with exceptionally high implantation rates . There are , however , only a few prospect i ve r and omized studies comparing day 3 versus day 5 embryo transfer . Furthermore , the number of embryos replaced in the day 3 group transfer is often higher than the number of blastocysts replaced , thereby affecting implantation rates . A total of 118 patients undergoing st and ard IVF/intracytoplasmic sperm injection who had developed at least three 8-cell embryos showing < 20 % extracellular fragmentation on day 3 were r and omized for day 3 or day 5 transfer . A maximum of two embryos were replaced . In this prospect i ve , r and omized study the implantation and pregnancy potential of embryos transferred on day 3 or day 5 were compared . Equal numbers of embryos were replaced in the two groups . There was no statistically significant difference between day 3 and day 5 transfer regarding positive human chorionic gonadotrophin rates ( 70 versus 67 % ) , clinical pregnancy rates ( 61 versus 51 % ) , implantation rates ( 44 versus 37 % ) , twinning rates ( 42 versus 41 % ) and rates of early pregnancy loss ( 15 versus 29 % ) . Transfer of embryos on day 3 or 5 showed similar implantation rates when equal numbers of embryos were transferred . Embryo transfer at the blastocyst stage seems to have no advantage over day 3 transfer in patients with more than two 8-cell embryos showing less than 20 % fragmentation on day 3 BACKGROUND This r and omized controlled study was performed in an unselected IVF/ICSI population to test the hypothesis that blastocyst transfers result in higher clinical pregnancy rates ( CPR ) per oocyte retrieval when compared with day 2 transfers . METHODS Blind r and omization for transfer on day 2 ( group 1 ) or day 5/6 ( group 2 ) was performed before stimulation . Oocytes and embryos were cultured in sequential media in 5.5 % CO(2 ) , 5 % O(2 ) , 89.5 % N(2 ) and 90 % humidity . A maximum of two embryos was transferred . RESULTS The two groups were similar for age , IVF indication  , number of treatment cycles , rate of ICSI/IVF , number of fertilized oocytes and number of embryos transferred . The CPR/oocyte retrieval was comparable in group 1 ( 32 % ) and in group 2 ( 44 % ) , while the CPR/embryo transfer was significantly higher ( P < 0.01 ) in group 2 ( 60 % ) than in group 1 ( 35 % ) . Similarly , the implantation rate per embryo transferred was significantly higher ( P < 0.03 ) in group 2 ( 46 % ) than in group 1 ( 29 % ) . The cryo-augmented delivery rate/oocyte retrieval was comparable in group 2 ( 36.3 % ) and in group 1 ( 28.6 % ) . CONCLUSION This r and omized study in an unselected population showed a significantly higher CPR/embryo transfer and a tendency toward a higher CPR/oocyte retrieval in patients receiving blastocysts when compared with day 2 transfers BACKGROUND The existence of a real benefit of blastocyst transfer is still a matter of debate . The aim of this study was to compare , in a prospect i ve r and omized trial , the outcome of day 2 and day 5 transfer of human embryos cultured in an ' in-house ' sequential medium . METHODS A total of 193 cycles from 171 patients with less than four previous IVF cycles , < 39 years old and with four or more zygotes on day 1 , were r and omly allocated to day 2 ( 94 cycles ) or day 5 ( 99 cycles ) transfer . Zygotes were kept in fertilization medium until 18 h post-fertilization and then placed in a ' glucose-free ' cleavage medium . Embryos allocated for day 5 transfer were placed in a blastocyst medium 66 h post-fertilization . Two or three embryos were replaced according to the morphology . RESULTS A mean ( + /- SEM ) number of 2.1 + /- 0.4 and 1.9 + /- 0.3 embryos were replaced on day 2 and day 5 ( P < 0.001 ) respectively . Delivery rates per transfer were 44.1 and 37.1 % [ P = not significant ( NS ) ] , implantation rates were 31.4 and 29.4 % ( NS ) and multiple delivery rates 22 and 36 % ( NS ) for day 2 and day 5 groups respectively . Ten patients ( 10.1 % ) had no blastocysts available for transfer . CONCLUSIONS No clear benefits were observed using blastocyst transfer for patients aged < 39 years who had had less than four previous IVF cycle attempts OBJECTIVES To compare the implantation rate of embryos after 3 and 5 days of IVF culture . DESIGN Prospect i ve r and omization of ET depending on the weekday of ovum pick-up ( OPU ) . SETTING University Department of Endocrinology and Reproduction . PATIENTS All women entering an outclinic IVF program . INTERVENTIONS Two hundred thirty-three ETs performed on day 3 after OPU and 410 performed on day 5 were analyzed . When blastocysts with a clear inner cell mass were available , a maximum of two were replaced . RESULTS On day 3 after OPU , 60 pregnancies per 233 ET ( 26 % ) and on day 5 , 102 pregnancies per 410 ET ( 25 % ) were induced . The average implantation rate per embryo was 13 % and 12 % , respectively . After subdivision according to embryo 
    Output:
    
REVIEW ER 'S CONCLUSIONS Overall this review of the best available evidence based on data from r and omised controlled trials , suggests that to date little difference in the major outcome parameters has been demonstrated between early embryo transfer and blastocyst culture .
The subgroup of trials employing sequential media , did however demonstrate a substantial improvement in implantation rates and similar pregnancy rates , despite the transfer of less embryos .