***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  Twin pregnancies after IVF are still frequent and are considered high-risk pregnancies leading to high costs . Transferring one embryo can reduce the twin pregnancy rate . We compared cost-effectiveness of one fresh cycle elective single embryo transfer ( eSET ) versus one fresh cycle double embryo transfer ( DET ) in an unselected patient population . METHODS Patients starting their first IVF cycle were r and omized between eSET and DET .  Societal costs per couple were determined empirically , from hormonal stimulation up to 42 weeks after embryo transfer . An incremental cost-effectiveness ratio ( ICER ) was calculated , representing additional costs per successful pregnancy . RESULTS Successful pregnancy rates were 20.8 % for eSET and 39.6 % for DET .  Societal costs per couple were significantly lower after eSET ( 7334 euro ) compared with DET ( 10,924 euro ) . The ICER of DET compared with eSET was 19,096 euro , meaning that each additional successful pregnancy in the DET group will cost 19,096 euro extra . CONCLUSIONS One cycle eSET was less expensive , but also less effective compared to one cycle DET . It depends on the society 's willingness to pay for one extra successful pregnancy , whether one cycle DET is preferred from a cost-effectiveness point of view BACKGROUND Embryologists currently face a challenge when counselling patients regarding the stage and the number of embryos to transfer when no top- quality embryos ( TQE ) are available . METHODS The aim of this study was to evaluate the efficacy of single blastocyst transfer ( SBT ) in comparison with the transfer of two cleavage-stage embryos in women under 36 years old . A total of 450 women under 36 years undergoing their first or second IVF treatment who had no TQE on Day 2 were included in this prospect i ve study . Couples were assigned to either a SBT or a double cleavage-stage embryo transfer ( DET ) . The clinical end-points monitored were rates of implantation , delivery and multiple deliveries . RESULTS The rate of transfer was significantly lower for couples assigned to the SBT group compared with the DET group ( 88 versus 100 % , respectively , P < 0.001 ) while the delivery rate per oocyte retrieval was similar in both groups ( 26.7 % ) . By contrast , the rate of multiple deliveries was significantly lower in the SBT group compared with the DET group ( 3.3 versus 23.3 % , respectively , P < 0.01 ) . Blastocyst cryopreservation was twice as high in the SBT group compared with the DET group ( 39 versus 18 % , respectively , P < 0.001 ) . CONCLUSIONS These findings show the value of extended embryo culture for couples without TQE . In such situations , delaying embryo transfer in order to select a single blastocyst with the highest potential for implantation can reduce the number of multiple pregnancies . Furthermore , our results demonstrate that extended culture allows blastocyst cryopreservation from embryos not available for Day 2 cryopreservation It is believed that delayed transfer of embryos after IVF allows for a better selection of good quality embryos . Hence , the number of embryos and all other prognostic factors being equal , transfer of day 3 embryos should be associated with higher implantation and pregnancy rates than transfer of day 2 embryos . To investigate this hypothesis , a prospect i ve r and omized study was carried out to compare implantation and pregnancy rates between day 2 and day 3 transfers . The relationship between the embryo quality score of day 2 and day 3 embryos and their respective implantation rates was also analysed . In a 2 year period all patients undergoing infertility treatment and in whom at least seven normally fertilized oocytes were obtained were included in the study . A minimization procedure was performed taking into account the patient 's age and the method of fertilization ( IVF or intracytoplasmic sperm injection ) . By using a uniform policy of embryo transfer , the number of embryos transferred was similar in both groups . The outcome parameters were embryo quality , implantation and pregnancy rates . No difference was observed in implantation and pregnancy rates between transfers on day 2 versus day 3 ( 23.8 versus 23.8 % and 47.9 versus 46.8 % respectively ) . The incidence of embryos of moderate to poor quality was higher in embryos cultured for 3 days compared with those cultured for 2 days . It is concluded that the outcomes of embryo transfer in terms of implantation and pregnancy rates are comparable for day 2 and day 3 embryos , although the overall embryo quality score decreases when embryos are kept in culture till day 3 OBJECTIVE To compare blastocyst-stage embryo transfers ( ETs ) with day 2 - 3 ETs in patients who failed to conceive in three or more day 2 - 3 IVF/ET cycles . DESIGN Prospect i ve , r and omized . SETTING Fertility unit in a university medical center . PATIENT(S ) Fifty-four patients with an adequate ovarian response underwent oocyte retrievals . The patients were prospect ively and r and omly divided into blastocyst-stage and day 2 - 3 ET groups . INTERVENTION(S ) Ovarian down-regulation was obtained using GnRH agonist , and controlled ovarian hyperstimulation was achieved using daily administration of gonadotropins . MAIN OUTCOME MEASURE(S ) The rate of blastocyst formation , ET cancellations , pregnancies , implantation , multiple gestation , and live births . RESULT ( S ) The clinical pregnancy rates per oocyte retrieval were 21.7 % and 12.9 % per blastocyst and day 2 - 3 ETs , respectively . Although there was a significantly higher implantation rate for blastocyst embryos ( 21.2 % ) as compared with 48- to 72-hour embryos ( 6 % ) , the multiple-pregnancy rate was not significantly different between both groups . An ET cancellation rate of 26 % and 6.4 % for blastocyst and day 2 - 3 ETs , respectively , was observed . The presence of two or more 8-cell embryos on day 3 in culture carried a high probability of obtaining blastocysts for transfer . CONCLUSION ( S ) This prospect i ve r and omized study suggests that in patients with an adequate ovarian response who failed to conceive in at least three IVF/ET cycles [ 1 ] . transfer of blastocyst-stage embryos carries a significantly higher implantation rate ; [ 2 ] . the pregnancy rate per oocyte retrieval and ET are higher in the blastocyst-stage group , even if it did not reach statistical significance ; [ 3 ] . a higher ET cancellation rate was observed in the whole blastocyst-stage group ; [ 4 ] . the ET cancellation rate was reduced significantly if the decision to proceed to blastocyst transfer was made on day 3 after oocyte retrieval , which is a post hoc conclusion The greatest risk element in any form of assisted conception , is the risk to a fetus within a multiple pregnancy , even with twin implantation . Recent research has examined the contribution of single embryo transfer in reducing the incidence of multiple gestation  within IVF . Two recent studies from our assisted conception centres have demonstrated that single embryo transfer can be undertaken without compromising the patient 's ultimate chance of having a successful ongoing pregnancy . The first study was a r and omized trial comparing the pregnancy rates in women having two embryos transferred at day two or three after oocyte collection , with that of a second group undergoing single blastocyst transfer .  The results revealed an equivalent ongoing pregnancy rate but a significant reduction in the twin rate ( to zero ) in the single transfer group . A second study examined the cumulative pregnancy rate in women with two or more suitable blastocysts after oocyte collection for transfer , when the final chance of pregnancy was calculated after all embryos had been transferred fresh and in subsequent frozen-thaw embryo transfers . The results were calculated for two groups of women in this data set , one receiving a single embryo for transfer fresh and the second group having two embryos transferred fresh . There was an initial improvement in the fresh embryo transfer group having two transferred ( 59 % vs 44 % for the single transfer group ) , but when additional pregnancies from frozen-thawed pregnancies were added , there was no difference in the final cumulative pregnancy rate in either group ( 74 % for the single transfer group and 70 % for the double transfer group ) . In contrast , 28 % of overall pregnancies in the ( initial ) double transfer group were multiple , whereas only 5 % of the ( initial ) single transfer group were twins . The development of high quality incubation systems within IVF that allow for both blastocyst culture and successful cryopreservation allow for both a high pregnancy rate and the development of strategies to reduce the multiple pregnancy rate 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 BACKGROUND We analysed the difference in maternal , neonatal and total costs after single ( SET ) versus double day 3 embryo transfer ( DET ) . METHODS We performed a two-centre prospect i ve study of women in their first IVF/ICSI cycle choosing between  SET or DET . Infertility treatment data were gathered from a data base ; maternal and neonatal outcome data from a case report form ( CRF ) ; health economic data from medical acts registered in the CRF for the outpatient part and from hospital bills . SET was performed in 206/367 ( 56.1 % ) and DET in 161/367 ( 43.9 % ) women . RESULTS In all , 367 transfers yielded 186 positive pregnancy tests , 148 ongoing pregnancies and 136 live deliveries ( 50.7 , 40.3 and 37.1 % per embryo transfer ) of which 15 ( 11.0 % ) were twins . Live birth rate was 37.4 % for SET , 36.6 % for DET . Intention-to-treat analysis showed differences for : duration of pregnancy ( SET : 39.0 + /- 1.4 versus DET : 38.3 + /- 2.2 weeks ; P = 0.055 ) , percentage prematurity ( 8.5 versus 23.8 % ; P = 0.033 ) , percentage of neonates hospitalized ( 5.7 versus 17.9 % ; P = 0.121 ) and duration of neonatal hospitalization ( 6.3 + /- 2.2 versus 10.3 + /- 10.1 days ; P = 0.01 ) . Total cost after DET was higher ( SET : 4700 + /- 3239 versus DET : 8613 + /- 10 105 ; P = 0.105 ) , due to significantly higher neonatal costs ( 451 + /- 957 versus 3453 + /- 8154 ; P < 0.001 ) and not to differences in maternal costs ( 4250 + /- 2882 versus 5160 + /- 4106 ; P = 0.152 ) . CONCLUSIONS This prospect i ve health economic study shows that transfer of a single top quality embryo is equally effective as , but substantially cheaper than , double embryo transfer in women < 38 years of age in their first IVF/ICSI cycle St and ard protocol s for in-vitro fertilization ( IVF ) include transfer of two or three embryos . Not surprisingly , the rate of twin pregnancy after IVF is high ( about 24 % of all pregnancies ) . Routine transfer of one , rather than two , embryos would be expected to result in a much lower rate of twin pregnancies at the cost of a lower take-home baby rate . The aim of this study was to compare hypoth 
    Output:
    
In a single fresh IVF cycle , single embryo transfer is associated with a lower live birth rate than double embryo transfer .
However , there is no evidence of a significant difference in the cumulative live birth rate when a single cycle of double embryo transfer is compared with repeated SET ( either two cycles of fresh SET or one cycle of fresh SET followed by one frozen SET in a natural or hormone-stimulated cycle ) .
Single embryo transfer is associated with much lower rates of multiple pregnancy than other embryo transfer policies .
A policy of repeated SET may minimise the risk of multiple pregnancy in couples undergoing ART without substantially reducing the likelihood of achieving a live birth .