***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: Ovarian stimulation with a GnRH-a and hMG for IVF treatment offers the potential to extend the period of follicle recruitment and growth free of the restriction imposed by a spontaneous midcycle LH surge . A r and omized trial investigating the impact of extending follicle growth by 1 day result ed in a significantly reduced PR , despite an increase in the number of larger follicles ( greater than or equal to 17 mm ) at the time of hCG . The reason for a reduced PR was not related to the number of ova recovered or embryo quality . This suggests that follicular aging or the duration of estrogen rise may be important OBJECTIVE To assess the effect of altering the timing of hCG administration on ongoing pregnancy rates in patients stimulated with recombinant FSH ( rec-FSH ) and GnRH antagonists for IVF . DESIGN Prospect i ve , r and omized , controlled trial . SETTING Tertiary referral center . PATIENT(S ) Four hundred thirteen patients undergoing IVF .  INTERVENTION(S ) Rec-FSH stimulation starting on day 2 of the cycle combined with daily GnRH antagonist starting on day 6 of stimulation . Patients were r and omized to receive 10000 IU of hCG either as soon as at least three follicles were > or=17 mm on ultrasound ( early-hCG group , 208 patients ) or 2 days later after this criterion was met ( late-hCG group , 205 patients ) . MAIN OUTCOME MEASURE(S ) Ongoing pregnancy rate . RESULT ( S ) Fertilization rates and number and quality of embryos transferred did not differ between the two groups . However , a significantly lower ongoing pregnancy rate was present in the late-hCG as compared with the early-hCG group ( 25.0 % vs. 35.6 % , respectively ) . CONCLUSION ( S ) Prolongation of the follicular phase in patients stimulated with rec-FSH and GnRH antagonists for IVF does not affect oocyte or embryo quality but is associated with a significantly lower ongoing pregnancy rate OBJECTIVE To determine if there is an optimum time for the administration of human chorionic gonadotropin ( hCG ) after pituitary desensitization with gonadotropin-releasing hormone agonists ( GnRH-a ) has been achieved before ovarian stimulation for in vitro fertilization ( IVF ) . DESIGN Prospect i ve r and omized study . PATIENTS Two hundred forty-seven patients undergoing an IVF treatment cycle who were r and omly divided into three groups . INTERVENTIONS All patients were administered subcutaneously buserelin acetate 500 micrograms/d from day 1 of the menstrual cycle . After pituitary desensitization had been achieved at least 14 days later , ovarian stimulation with human menopausal gonadotropin was commenced . Ovarian stimulation , cycle monitoring , oocyte recovery , and IVF and embryo transfer ( ET ) techniques were identical in all three groups . Patients in group 1 ( n = 79 ) had hCG administered when the mean diameter of the largest follicle had reached 18 mm , at least two other follicles were greater than 14 mm , and serum estradiol ( E2 ) levels were consistent with the number of follicles observed on ultrasound . Patients in groups 2 ( n = 84 ) and 3 ( n = 84 ) had hCG administered 1 day and 2 days , respectively , after the above criteria had been reached . RESULTS The mean day of hCG administration ( P less than 0.01 ) , maximum serum E2 concentration ( P = 0.06 ) , number of days of serum E2 rise ( P = 0.03 ) , and mean diameter of the largest follicle ( P less than 0.0001 ) were significantly different . There were , however , no significant differences in the mean number of preovulatory and medium size follicles , number of oocytes recovered or embryos transferred . There were also no significant differences in the oocyte recovery , fertilization and cleavage rates , in the number of embryos frozen , or in the pregnancy rates per initiated cycle and per ET . CONCLUSIONS There is no significant advantage in the precise timing of hCG administration after pituitary desensitization with GnRH-a OBJECTIVE To investigate whether the deleterious effect of E(2 ) on embryonic implantation is due to a direct effect on the endometrium , on the embryo , or both . DESIGN Prospect i ve , controlled in vitro study . SETTING Tertiary infertility center . PATIENT(S ) Fertile patients in the luteal phase with histologically normal endometrium who were attending the infertility clinic as oocyte donors ( n = 14 ) . INTERVENTION(S ) E(2 ) dose-response ( 0 , 10(-8 ) , 10(-7 ) , 10(-6 ) , 10(-5 ) , and 10(-4 ) M ) and time course ( day 2 vs. day 5 ) experiments were performed in an in vitro embryo adhesion assay composed of human polarized endometrial epithelial cells obtained from fertile patients and mouse embryos . MAIN OUTCOME MEASURE(S ) Blastocyst formation rate and embryo adhesion rate . RESULTS Monolayers of polarized endometrial epithelial cells expressed ERalpha at the mRNA level . The E(2 ) dose response of blastocysts with polarized endometrial epithelial cells ( n = 235 ) demonstrated a progressive reduction in embryonic adhesion that was statistically significant at 10(-6 ) M. When polarized endometrial epithelial cells were treated alone with increasing doses of E(2 ) for 3 days and E(2 ) was then removed and blastocysts added ( n = 410 ) , embryonic adhesion was not significantly reduced , except at 10(-4 ) M. When 2-day mouse embryos ( n = 609 ) were treated with increasing E(2 ) concentrations until day 5 , the rate of blastocyst formation significantly decreased at a concentration > or= 10(-6 ) M , and embryonic adhesion decreased when blastocysts ( n = 400 ) were obtained at a concentration > or= 10(-7 ) M. Time course experiments of embryos cultured for 2 days with polarized endometrial epithelial cells ( n = 426 ) showed that the adhesion rate was higher at E(2 ) levels of 10(-7 ) , 10(-6 ) and 10(-5 ) M compared with embryos cultured for 5 days ( n = 495 ) . CONCLUSION ( S ) High E(2 ) levels are deleterious to embryo adhesion in vitro , mainly because they have a direct toxic effect on the embryo that may occur at the cleavage stage OBJECTIVE To assess the value of different serum E(2 ) cut-off levels for predicting women at risk for ovarian hyperstimulation syndrome ( OHSS ) . DESIGN Retrospective case-control study of a cohort of women undergoing assisted reproduction treatment ( ART ) over 12 months . SETTING Tertiary university hospital . PATIENT(S ) The study group included women with OHSS who fulfilled the endocrine inclusion criteria ( n = 40 ) . The control group was a r and om sample ( n = 40 ) from the cohort of women undergoing ART .  INTERVENTION(S ) None . MAIN OUTCOME MEASURE(S ) To evaluate the sensitivity and specificity of different serum E(2 ) cut-off levels on day 11 of ovarian stimulation in preventing the establishment of OHSS . RESULT ( S ) Three hundred ninety-nine cycles  ( IVF and intracytoplasmic sperm injection ) were undertaken between June 2000 and May 2001 . The study group ( n = 40 ) was compared with the control group ( n = 40 ) undergoing ART during the same period of time . On day 8 of ovarian stimulation , the mean ( SD ) E(2 ) level in the study group was 8,517(5.3 ) pmol/L ( 2,320 pg/mL ) , and in the control group it was 2,540 ( 2.6 ) pmol/L ( 691 pg/mL ) . On day 11 of stimulation the mean ( SD ) E(2 ) level was 15,662 ( 4.2 ) pmol/L ( 4,266 pg/mL ) and 5,804 ( 4.5 ) pmol/L ( 1,581 pg/mL ) , respectively . Twenty-four ( 60 % ) women who developed OHSS had E(2)levels > 6,000 pmol/L ( 1,634 pg/mL ) on day 8 and above 11,000 pmol/L ( 2,996 pg/mL ) on day 11 . Sixteen ( 40 % ) had E(2 ) levels < 6,000 pmol/L ( 1,634 pg/mL ) on day 8 , but all had levels above 11,000 pmol/l ( 2,996 pg/mL ) on day 11 . CONCLUSION ( S ) A serum E(2 ) level of 12,315 pmol/L ( 3,354 pg/mL ) on day 11 of ovarian stimulation gives a sensitivity and specificity of 85 % for the detection of women at risk for OHSS OBJECTIVE To analyze the effect on uterine receptivity of a decrease in E2 levels during the preimplantation period with the use of a step-down regimen in high responders undergoing IVF .  DESIGN Prospect i ve controlled clinical study . SETTING The Instituto Valenciano de Infertilidad . PATIENT(S ) High responders in whom at least one previous IVF attempt failed in which 3 - 4 good- quality embryos were transferred and E2 levels were > 3,000 pg/mL on the day of hCG administration . INTERVENTION(S ) Gonadotropins were administered according to two different protocol s. Blood sample s were collected and IVF was performed . MAIN OUTCOME MEASURE(S ) Serum E2 levels and reproductive outcome of IVF .  RESULT ( S ) Estradiol levels on the day of hCG administration and throughout the preimplantation period and the number of oocytes collected were significantly lower with the use of the step-down regimen than during the previous failed cycle in which the st and ard protocol was used . The fertilization rate was similar and the number of good- quality embryos transferred was comparable . However , the implantation and pregnancy rates were significantly improved in patients who underwent the step-down regimen compared with those who received the st and ard protocol . CONCLUSION ( S ) With the use of a step-down regimen with FSH in high responders , our clinical results demonstrate that uterine receptivity can be improved when E2 levels are decreased during the preimplantation period OBJECTIVE To determine serum E2 and P levels around the time of implantation in normal and high IVF responders . SETTING In Vitro Fertilization program at the Instituto Valenciano de Infertilidad . PATIENTS Twenty-nine women undergoing IVF , who accepted to be studied daily , were classified according to the number of oocytes retrieved in normal ( n = 16 ) and high responders ( n = 13 ) . DESIGN Prospect i ve study in which blood was drawn daily from the day of hCG administration ( day 0 ) up to 7 days later ( day 6 ) . MAIN OUTCOME MEASUREMENTS In vitro fertilization parameters ( number of ampules , FSH-hMG , number of oocytes , fertilization rates , number of transferred embryos , implantation rates , and pregnancy rates ) ; serum E2 and P levels during the 7 days of the study . RESULTS Implantation rate was significantly higher in normal ( 18.5 % ) as compared with high ( 0 % ) responders . Estradiol and P levels were elevated significantly in high responders . The E2:P ratio was significantly different between normal and high responders during the preimplantation period . Pregnancy and implantation rates decreased as serum E2 levels increased on days 4 to 6 of the study . CONCLUSIONS A different endocrine milieu between normal and high responders is detected by daily steroid measurements up to the preimplantation period , suggesting that this difference could be responsible for an impaired implantation in high responder patients undergoing IVF . An increase in serum E2 levels seems to be the cause of this difference Publication bias is defined as any tendency on the part of investigators or editors to fail to publish study results on the basis of the direction or strength of the findings . This may lead to overestimation of treatment effects in published work . Inappropriate decisions about patient management may result . We investigated what proportion of abstract s at the European Society of Human Reproduction and Embryology ( ESHRE ) annual meeting eventually reached full publication , what was the time to publication , and which factors might have affected publication . Among the 2691 abstract s of six ESHRE annual meetings , 151 ( 5.6 % ) reporting r and omized controlled trials ( RCT ) were identified . Comprehensive search es of electronic data bases and h and search ing of the two major journals in the field yielded 79 full publications pertaining to these abstract s. Kaplan-Meier analysis estimated 56 % of RCT abstract s to be eventually published in full , the median time to publication being 32.5 months . Positive outcome ( i.e. significant results ) did not affect the publication rate , and neither did sample size , the subject category , or the native language ( English/non-English ) of the country of origin . Oral presentations result ed in eventual full publication significantly more frequently ( 69 % ) than posters ( 42 % ) . It is 
    Output:
    
CONCLUSIONS Currently there is no high- quality evidence to support or deny the value of E2 determination on the day of hCG administration for  pregnancy achievement in IVF cycles , where pituitary down-regulation is performed with GnRH agonists .
Existing retrospective studies suggest that there is no positive association .