***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 BACKGROUND Implantation failure is the main limiting factor for success of IVF . Even when transfer techniques are carried out extremely carefully , embryo transfer may produce an endometrial and cervical reaction that may result in an inflammatory response and impaired implantation . There are no formal specifications on the use of indomethacin in reproductive cycles and there are no studies published in the scientific literature on its effect on embryo implantation . Oocyte donation is the best model to evaluate the determinants of implantation . The aim of this study is to evaluate the potential benefit of indomethacin administered at embryo transfer . METHODS A r and omized pilot trial of 136 oocyte recipients was carried out . Seventy-two women received st and ard specifications  plus 100 mg of indomethacin rectally given as three doses every 12 h starting on the night prior to transfer . RESULTS Positive HCG ( > = 6 mUI/ml ) occurred in 59.7 % of treated women and in 59.4 % of women in the control group . Implantation rates were 27.8 % in the indomethacin group and 26.4 % in the controls . CONCLUSIONS The indomenthacin group did not show significantly higher implantation rates . A larger study exploring alternative treatment protocol s might be appropriate Purpose : The objective of the matched , controlled study was to determine whether low-dose aspirin therapy without heparin improves pregnancy rates following frozen embryo transfer . Methods : Thirty-six women who did not achieve a pregnancy following fresh embryo transfer and who had frozen embryos available for another transfer were included . Eighteen women were treated with 81 mg aspirin from day 2 of the cycle through pregnancy testing . If the β-human chorionic gonadotropin level was positive , aspirin was continued through the pregnancy . Eighteen women were not given aspirin . The mean outcome variables were pregnancy and implantation rates . Results : The clinical pregnancy rate in the aspirin group was 11.1 % , compared with 33.3 % for the controls , and implantation rates were 2.9 and 10.9 % , respectively . Conclusions : No positive effects of low-dose aspirin therapy on pregnancy rates following frozen embryo transfer were observed The effect that gonadotrophin-releasing hormone ( GnRH ) antagonists exert on endometrial receptivity has not yet been eluci date d. GnRH antagonists might directly affect oocytes , the embryo and /or the endometrium . The aim of this study was to investigate the direct effect of GnRH antagonists on the endometrium in oocyte donation cycles . In an oocyte donation programme , oocytes from each donor ( n = 49 ) , stimulated with gonadotrophins and a GnRH antagonist , were equally shared between two different matched recipients . Recipients were r and omly allocated to either receive a GnRH antagonist concomitant to donor during their endometrial priming with oestradiol ( group I , n = 49 ) or to solely continue with their endometrial preparation ( group II , n = 49 ) . Pregnancy rate was 55.1 % in group I and 59.1 % in group II . Implantation rate was 26.1 % in group I and 24.4 % in group II . Endometrial thickness was also similar between the two groups on the day of human chorionic gonadotrophin injection to the donor . In conclusion , GnRH antagonist administration during the proliferative phase at a dose of 0.25 mg per day does not appear to adversely affect endometrial receptivity in oocyte recipients The effect of low-dose human chorionic gonadotropin ( hCG ) administration in the proliferative phase of oocyte recipients was investigated in a prospect i ve r and omized trial . Sibling oocytes from the same donor were shared at r and om among two different recipients . In group I oocyte recipients received 750 IU of hCG every three days concomitant to endometrial preparation with estradiol until hCG injection to the donor , whereas in group II recipients received no hCG during endometrial priming with estradiol . Endometrial thickness was significantly lower in group I compared with group II , although similar endometrial thickness was detected during the mock cycle . Pregnancy rates were significantly lower in group I than in group II ( 13.6 % vs. 45.4 % , p<0.05 ) . Implantation rates were also significantly lower in group I ( 1.7 % vs. 22.4 % , p<0.01 ) . The study was discontinued prematurely for ethical reasons when 22 cycles were completed , as pregnancy rates were very low in group I. In conclusion , hCG administration in the proliferative phase might directly affect endometrial proliferation and receptivity PURPOSE To determine if sildenafil improves endometrial thickness better than vaginal estradiol ( E2 ) in women with a history of thin endometria . METHODS Women failing to attain an 8 mm endometrial thickness on either the oocyte retrieval cycle or their first frozen embryo transfer ( ET ) despite an oral graduated E2 regimen were treated again with graduated oral E2 and were also r and omly assigned to vaginal sildenafil or vaginal E2 therapy .  Endometrial thickness was compared between the groups . RESULTS Neither vaginal E2 nor sildenafil significantly improved endometrial thickness or blood flow in the subsequent frozen ET-cycle . CONCLUSIONS These data fail to corroborate previous cl aims that 25 mg sildenafil four times daily intravaginally can improve endometrial thickness A polysyloxane vaginal ring containing 1 g of natural progesterone was developed as luteal supplementation for women treated with IVF-embryo transfer and for agonadal women participating in an oocyte donation programme . The ring provides continuous release of progesterone ( 10 - 20 nmol/l ) for 90 days . The efficacy of this form of progesterone supplementation was evaluated in two multicentre prospect i ve r and omized trials . IVF-embryo transfer trial : After oocyte aspiration , 505 women were r and omly allocated to progesterone supplementation with vaginal ring or i.m . progesterone ( 50 mg/day ) . The clinical pregnancy rate was 36.6 % in both groups . Implantation rate was 15.9 % in the vaginal ring and 16.0 % in i.m . progesterone . Oocyte donation trial : After endometrial proliferation with micronized oestradiol , 153 women were allocated to progesterone replacement with a vaginal ring or i.m . progesterone ( 100 mg/day ) . Clinical pregnancy rate was 39.8 and 28.6 % respectively . Implantation rate was significantly higher with the vaginal ring compared with i.m . progesterone ( 19.9 and 11.6 % respectively , P = 0.006 ) . The vaginal ring is a novel development which provides continuous release of progesterone for 90 days . In IVF-embryo transfer , its effectiveness is similar to daily i.m . injections . In oocyte donation the ring provides a progestative milieu which improves the implantation rate and eliminates the discomfort of daily i.m . injections Evidence accumulated in in-vitro fertilization ( IVF ) cycles suggests that the use of long-acting forms of gonadotrophin-releasing hormone analogues ( GnRHa ) for pituitary desensitization may impair the outcome of IVF as compared to classical short-acting formulations . Whether the negative effects are directed against the corpus luteum , the endometrium , or both is unknown . However , the presence of high affinity binding sites for gonadotrophin-releasing hormone ( GnRH ) in the human endometrium suggests a possible role of these analogues on this target organ , affecting embryo implantation . In the present study , we tested direct effects of two different forms of GnRHa on implantation using the ovum donation model . Patients were prospect ively allocated to one of the three study groups : the short-acting form of the analogue leuprolide acetate ( group I ; n=64 ) , the long-acting form of the same analogue ( group II ; n=58 ) , and the long-acting preparation of the analogue tryptorelin ( group III ; n=61 ) . A total of 68 cycles of embryo transfer was carried out in group I , whereas 67 were performed in group II and 65 in group III . Cancellation rates were respectively 18.1 , 17.3 and 18.8 % because of bleeding while being on the waiting list for anonymous oocyte donation . The number of oocytes donated , fertilization rates and embryos replaced in each group were similar . As a result , pregnancy rate per transfer was 38.2 , 49.3 and 44.6 % respectively . Implantation rates per embryo replaced were respectively 13.4 , 19.1 and 17.0 % . These data suggest that the use of a long-acting form of GnRHa provides success rates similar to the short-acting preparations , result ing in more convenient medication for patients with ovarian function included in ovum donation programmes A simple programmed thaw cycle is described , during which the endometrium is prepared with oral oestradiol , followed by a natural progesterone source . This method involves minimal blood tests and uses inexpensive medications . Originally , an i.m . progesterone-in-oil preparation was used . Although highly successful in achieving high serum progesterone concentrations , the daily injections of the oily compound were found to be problematic from the patients ' perspective . To examine the possibility of replacing the injectable progesterone with a vaginal preparation we conducted a prospect i ve r and omized study of 1 year 's duration , during which time 170 and 184 thawing cycles were done with injectable and vaginal progesterone respectively . Although the progesterone blood concentrations obtained with the injectable preparation were more than twice those obtained with the vaginal progesterone , the clinical pregnancy rates ( defined as percentage thawing cycles with gestational sac(s)/embryo transfer as demonstrated on ultrasound , 4 weeks after embryo transfer ) were similar for both groups ( 15.9 and 16.8 % respectively ) . Implantation and abortion rates were also comparable . These results agree with previous reports of higher uterine progesterone concentrations after the vaginal application . We conclude that the combination of oral oestradiol and vaginal progesterone is an effective , simple and inexpensive approach for programmed thaw cycles OBJECTIVE To evaluate the effect of low-dose aspirin use in oocyte donation recipients with an endometrial thickness of < 8 mm . DESIGN A prospect i ve , r and omized study . SETTING An oocyte donation program in a private infertility practice . PATIENT(S ) Twenty-eight recipients undergoing oocyte donation who failed to develop an 
    Output:
    
No significant benefit was demonstrated when using GnRH agonists .
No evidence of statistically significant benefit was found for one GnRH agonist over another , or vaginal over intramuscular progesterone administration .
No difference in pregnancy rate was demonstrated when no treatment was compared to aspirin , steroids , ovarian stimulation , or human chorionic gonadotropin ( hCG ) prior to embryo transfer , although using hCG several times before the oocyte retrieval decreases the pregnancy rate .
There is insufficient evidence to recommend any one particular protocol for endometrial preparation over another with regard to pregnancy rates after embryo transfers .
However , there is evidence of a lower pregnancy rate and a higher cycle cancellation rate when the progesterone supplementation is commenced prior to oocyte retrieval in oocyte donation cycles .