***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 
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    ***EXAMPLES*** 
    Input: Transfer of frozen-thawed embryos is usually carried out in a natural cycle or in a programmed cycle in which the endometrium is exogenously stimulated following down-regulation of the hypophysis . To analyse the possibility that the programmed cycle for embryo transfer can still be hormonally manipulated without the use of gonadotrophin-releasing hormone agonist ( GnRHa ) we have conducted a prospect i ve r and omized study that compared the outcome of frozen-thawed embryo transfer cycles using micronized 17beta-oestradiol and micronized progesterone preparations with and without the concomitant use of GnRHa .  One hundred and six patients were r and omly divided into two groups . In group A ( 53 patients ) 4 mg/day of micronized 17beta-oestradiol was initiated following down-regulation of hypophysis . In group B ( 53 patients ) oestrogen stimulation started on day 1 of the cycle without prior pituitary down-regulation using a dose of 6 mg/day for 7 days . In both groups , micronized progesterone in a dose of 900 mg/day was administered vaginally after at least 12 days of oestrogen stimulation . Embryo transfer embryo transfer took place 48 - 72 h thereafter according to the cryopreserved embryonic stage . Overall , none of the patients had any follicular development and only one cycle in group B had to be cancelled because of premature progesterone secretion . The two groups did not differ in age ( 31+/-5.6 and 31+/-5.0 years ) , number of embryos transferred per patient ( 3.4+/-1.2 and 3.3+/-1.0 ) , and day of progesterone initiation ( 15+/-2.2 and 15+/-1.9 for groups A and B respectively ) . The endometrial thickness on the day of progesterone initiation was comparable in both groups ( 11 + /-1.6 and 10+/-1.6 mm for groups A and B respectively ) . Similarly , the pregnancy rate per embryo transfer and implantation rate in group A ( 26.4 % and 9.5 % ) were comparable to those of group B ( 21.1 % and 9 % ) . These results indicate that programmed cycles can be successfully applied by administering a high dose of micronized 17beta-oestradiol starting on day 1 of the cycle . Compared to GnRHa programmed cycles , this approach is simpler , more convenient for both the patient and medical staff , and results in a similar success rate at a lower cost Purpose To evaluate the outcome of frozen-thawed embryo transfer ( FET ) when freezing takes place at the pronuclear stage , a retrospective analysis was performed comparing spontaneous and artificial cycles . Methods 148 women received FET in a spontaneous cycle ( Group A ) and 55 women received FET in an artificial cycle ( Group B ) induced by administering estrogen ( E2 ) and progesterone ( P ) .  Pregnancy rates , endometrial thickness and serum levels of E2 , P and luteinizing hormone ( LH ) were measured . Statistical analysis included the mean , the st and ard deviation , the Chi-squared test and the T-test . Results The clinical pregnancy rate was 34.5 % for Group A and 21.8 % for Group B ( p = 0.084 ) , with a live birth rate of 20.9 % and 12.7 % respectively ( p = 0.15 ) . There was no difference in endometrial thickness or the P levels , while LH and E2 levels were significantly higher in group B ( p < 0.0001 ) . Conclusion Our retrospective study shows a trend towards higher pregnancy rates and live birth rates with the administration of FET during a spontaneous cycle compared to FET during an artificial cycle . Large r and omized controlled trials are needed to confirm this trend In a r and omized multicenter study , the efficacies of two different GnRH agonists were compared with that of hCG for triggering final stages of oocyte maturation after ovarian hyperstimulation for in vitro fertilization . Ovarian stimulation was conducted by recombinant FSH ( Puregon ) , and the GnRH antagonist ganirelix ( Orgalutran ) was coadministered for the prevention of a premature LH rise . Luteal support was provided by daily progestin administration . Frequent blood sampling was performed at midcycle in the first 47 eligible subjects included in the current study , who were r and omized for a single dose of 0.2 mg triptorelin ( n = 17 ) , 0.5 mg leuprorelin ( n = 15 ) , or 10,000 IU hCG ( n = 15 ) . Serum concentrations of LH , FSH , E2 , and progesterone ( P ) were assessed at variable intervals . LH peaked at 4 h after both triptorelin and leuprorelin administration , with median LH levels of 130 and 107 IU/liter ( P < 0.001 ) , respectively . LH levels returned to baseline after 24 h. Subjects receiving hCG showed peak levels of 240 IU/liter hCG 24 h after administration . A rise in FSH to 19 IU/liter ( P < 0.001 ) was noted in both GnRH agonist groups 8 h after injection . Within 24 h the areas under the curve for LH and FSH were significantly higher ( P < 0.001 ) in both GnRH agonist groups compared with that for hCG . E2 and P levels were similar for all groups up to the day of oocyte retrieval . Luteal phase areas under the curve for P and E2 were significantly elevated ( P < 0.001 ) in the hCG group . The mean ( + /-SD ) numbers of oocytes retrieved were 9.8 + /- 5.4 , 8.7 + /- 4.5 , and 8.3 + /- 3.3 ; the percentages of metaphase II oocytes were 72 % , 85 % , and 86 % ; and fertilization rates were 61 % , 62 % , and 56 % in the triptorelin , leuprorelin , and hCG group , respectively ( P = NS for all three comparisons ) . These findings support the effective induction of final oocyte maturation in both GnRH agonist groups . In summary , after treatment with the GnRH antagonist ganirelix for the prevention of premature LH surges , triggering of final stages of oocyte maturation can be induced effectively by a single bolus injection of GnRH agonist , as demonstrated by the induced endogenous LH and FSH surge and the quality and fertilization rate of recovered oocytes . Moreover , corpus luteum formation is induced by GnRH agonists with luteal phase steroid levels closer to the physiological range compared with hCG . This more physiological approach for inducing oocyte maturation may represent a successful and safer alternative for in vitro fertilization patients undergoing ovarian hyperstimulation The efficacy of three protocol s of endometrial preparation ( spontaneous cycles , A : artificial preparation , B ; ovarian stimulation , C ) for cryopreserved-thawed human embryo transfer ( CT-ET ) . The implantation and clinical pregnancy rates per cycle in 236 women undergoing 381 consecutive CT-ETs  were evaluated according to the endometrial preparation protocol . No statistically significant difference was found in implantation rates per embryo transfer ( A = 5.6 % , B = 5.6 % , C = 4.6 % ) and clinical pregnancy rates per cycle ( A = 16.9 % , B = 16.5 % , C = 15.6 % ) between the three endometrial preparation protocol s used . In conclusion , the specific method of endometrial preparation for CT-ET had no significant impact upon the implantation rate OBJECTIVE To assess whether there is a difference in the ongoing pregnancy rate after transferring frozen-thawed embryos in natural cycles with spontaneous LH-P rise compared with natural cycles controlled by hCG for final oocyte maturation and ovulation . DESIGN R and omized controlled trial . SETTING Tertiary referral center . PATIENT(S ) A total of 168 patients were assigned r and omly to undergo frozen ET on day 3 from October 2007 until November 2008 . Finally , analysis was performed in 124 patients ; 61 belonged to the spontaneous LH group and 63 to the hCG group . INTERVENTION(S ) In the spontaneous LH group the transfer was planned 5 days after the LH surge . In the hCG group , the cryopreserve ET was planned 5 days after the administration of 5000 IU of hCG , when an endometrial thickness of ≥7 mm and a follicle of ≥17 mm were present on ultrasound examination . MAIN OUTCOME MEASURE(S ) Ongoing pregnancy rate . RESULT ( S ) The study was terminated early , when a prespecified interim analysis found a significantly higher ongoing pregnancy rate in the spontaneous LH group as compared with the hCG group ( 31.1 % vs. 14.3 % ; difference 16.9 % , 95 % confidence interval 4.4%-28.8 % ) . CONCLUSION ( S ) The results suggest the superiority of the natural cycle as compared with the natural cycle controlled by hCG administration in cryothawed ET cycles OBJECTIVE To see if progesterone support has a beneficial effect on live birth rate after frozen embryo transfer in natural cycles . DESIGN Prospect i ve r and omized controlled trial . SETTING University-based hospital . SUBJECT(S ) Four hundred thirty-five women undergoing embryo transfer in natural cycles . INTERVENTION(S ) The women received either vaginal progesterone , 400 mg twice a day from the day of embryo transfer in natural cycles , or no progesterone support . MAIN OUTCOME MEASURE(S ) Live birth rate , biochemical pregnancy rate , pregnancy rate , and spontaneous abortion rate . RESULT ( S ) Live birth rate were significantly greater in women receiving vaginal progesterone as luteal phase support after frozen-thawed embryo transfer in natural cycles compared with those who did not take progesterone . There were no differences in biochemical pregnancy rate , pregnancy rate , or spontaneous abortion rate . CONCLUSION ( S ) Progesterone supplementation improves live birth rate after embryo transfer in natural cycles Purpose To evaluate the clinical efficacy of letrozole on ovulation induction and hormone replacement therapy ( HRT ) during endometrial preparation for frozen – thawed embryo transfer ( FET ) . Methods We analyzed totally 1,230 cycles of patients that underwent FET from October 2010 to September 2012 . Seven hundred and thirteen cycles of patients with ovulation disorders that underwent FET were r and omly assigned to two groups by case control study . 359 cycles received letrozole ovulation induction and 354 cycles received HRT during endometrial preparation for FET , respectively . In the corresponding period , 517 cycles of patients with normal ovulation in the natural cycle group for FET endometrial preparation served as controls . Reproduction-related clinical outcomes of patients in the three groups were compared . Results The embryo implantation rate of patients in letrozole group ( 30.4 % ) was significantly higher than the HRT group ( 22.8 % , P < 0.05 ) . The clinical pregnancy rate of patients in the letrozole group ( 53.2 % ) was significantly higher than the HRT group ( 44.4 % , P < 0.05 ) , while no significant difference was observed between the letrozole and natural cycle groups ( 51.3 % , P > 0.05 ) . Estradiol levels on the day of human chorionic gonadotropin administration in the letrozole group were significantly lower than those in the natural cycle group ( 280.32 ± 125.39 pg/ml and 351.06 ± 123.03 pg/ml , respectively ; P < 0.05 ) . The live birth rate of patients in letrozole group ( 44.6 % ) was significantly higher than the HRT group ( 32.5 % , P < 0.05 ) , while abortion rate ( 12.0 % ) was significantly lower than the HRT group ( 21.0 % , P < 0.05 ) . There were no significant differences in number of mature follicles , endometrial thickness , duration of follicle growth between the letrozole and the natural cycle groups , and there were no significant differences in twin birth rate and ectopic pregnancy rate among the three groups ( all P values > 0.05 ) . Conclusions Ovulation induction with letrozole during endometrial preparation for FET has a higher rate of pregnancy success and a lower abortion rate than HRT . Letrozole treatment exhibits clinical progression and outcomes similar to those patients undergoing a natural cycle or normal ovulation cycle . Therefore , letrozole treatment may be an effective option in endometrial preparation for FET in patients with ovulation disorders or irregular menstruation Background : The transfer of cryopreserved embryos can be timed with ovulation in a natural cycle or after artificially preparing the endometrium with exogenous hormones . Progesterone is essential for the secretory transformation of the endometrium that permits implantation as well as maintenance of early pregnancy . The purpose of this study is to assess the effect of luteal phase supplementation on pregnancy rates in natural frozen-thawed cycles . Material s and Methods : The study was design ed as a prospect i ve r and omized clinical trial of 102 women who underwent embry 
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Results No statistically significant difference for both clinical pregnancy and live birth was noted between tNC and mNC groups .
When tNC and AC without suppression groups are compared , there was a statistically significant difference in clinical pregnancy rate in favor of tNC , whereas it failed to reach statistical significance for live birth .
When tNC and AC with suppression groups are compared , there was a statistically significant difference in live birth rate favoring the latter .
Similar pregnancy outcome was noted among mNC versus AC with or without suppression groups .
Similarly , no difference in clinical pregnancy and live birth was noted when ACs with or without suppression groups are compared .
Conclusions There is no consistent superiority of any endometrial preparation for FER .
However , mNC has several advantages ( being patient-friendly ; yielding at least equivalent or better pregnancy rates when compared with tNC and AC with or without suppression ; may not require LPS ) .
Mild OS with Gn or AI may be promising