***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: OBJECTIVES : To compare the efficacy of letrozole and clomiphene citrate ( CC ) in patients of anovulatory polycystic ovarian syndrome ( PCOS ) with infertility . MATERIAL S AND METHODS : This prospect i ve r and omized clinical trial included 204 patients of PCOS . 98 patients ( 294 cycles ) received 2.5–5 mg of letrozole ; 106 patients ( 318 cycles ) received 50–100 mg of CC ( both orally from Days 3–7 of menstrual cycle ) . The treatment continued for three cycles in both the groups . Main outcome measures : ovulation rate , endometrial thickness , and pregnancy rate . Statistical analysis was done using SPSS 13 software . P value less than 0.05 was considered significant . RESULTS : The mean number of dominant follicles in letrozole groups and CC groups was 1.86±0.26 and 1.92±0.17 , respectively ( P=0.126 ) . Number of ovulatory cycle  in letrozole group was 196 ( 66.6 % ) versus 216 ( 67.9 % ) in CC group ( P=0.712 ) . The mean mid-cycle endometrial thickness was 9.1±0.3 mm in letrozole group and 6.3±1.1 in CC group , which was statistically significant ( P=0.014 ) . The mean Estradiol [ E2 ] level  in clomiphene citrate group was significantly higher in CC group ( 364.2±71.4 pg/mL ) than letrozole group ( 248.2± 42.2 pg/mL ) . 43 patients from the letrozole group ( 43.8 % ) and 28 patients from the CC group ( 26.4 % ) became pregnant . CONCLUSION : Letrozole and CC have comparable ovulation rate . The effect of letrozole showed a better endometrial response and pregnancy rate compared with CC OBJECTIVE : To compare Letrozole ( 5 mg ) and clomiphene citrate ( 100 mg ) as first line ovulation induction drug in infertile PCOS women . STUDY DESIGN : Prospect i ve R and omised trial . SETTING : A Tertiary level infertility centre . Patients : 103 infertile PCOS women INTERVENTION(S ) : Treatment naïve infertile PCOS women were r and omised to treatment with 5 mg letrozole ( 51 patients ) or 100 mg clomiphene citrate ( 52 patients ) daily starting day 2 to day 6 of menstrual cycle . Timed intercourse or Intra Uterine Insemination ( IUI )  was advised 24 to 36 hours after Human Chorionic Gonadotropin ( HCG ) injection . MAIN OUTCOME MEASURES : Ovulation rate , mono or multi follicular rate , days to ovulation , endometrial thickness , serum progesterone , serum estrogen , pregnancy rate , miscarriage rate . RESULTS : The mean age , Body Mass Index ( BMI ) , duration of infertility in both Clomiphene Citrate ( CC ) and Letrozole groups were similar . Ovulation rate was 73.08 % in letrozole group and 60.78 % in CC , which was not statistically significant ( P=0.398 ) . There was no statistically significant difference between Endometrial thickness ( CC 7.61 ±1.96 , Let 7.65 ± 2.10 ) , Sr E2 on day of HCG ( CC 178.3 ± 94.15 , Let 162.09 ± 73.24 ) , Days to ovulation ( CC 14.2 ± 3.41 ; Let 13.13 ± 2.99 ) and Sr P4 on D21 ( CC 10.58 ± 6.65 ; Let 11.86 ± 6.51 ) . Monofolliculo genesis ( CC 54.84 , Let 79.49 % , P=0.027 ) and Pregnancy rate ( CC 7.84 % , Let 21.56 % P=0.0125 ) were statistically significantly higher in letrozole group . CONCLUSION : Our study shows that letrozole has excellent pregnancy rates compared to clomiphene citrate . Letrozole should be considered at par with clomiphene citrate as first line drug for ovulation induction in infertile PCOS women BACKGROUND Clomiphene is the current first-line infertility treatment in women with the polycystic ovary syndrome , but aromatase inhibitors , including letrozole , might result in better pregnancy outcomes . METHODS In this double-blind , multicenter trial , we r and omly assigned 750 women , in a 1:1 ratio , to receive letrozole or clomiphene for up to five treatment cycles , with visits to determine ovulation and pregnancy , followed by tracking of pregnancies . The polycystic ovary syndrome was defined according to modified Rotterdam criteria ( anovulation with either hyper and rogenism or polycystic ovaries ) . Participants were 18 to 40 years of age , had at least one patent fallopian tube and a normal uterine cavity , and had a male partner with a sperm concentration of at least 14 million per milliliter ; the women and their partners agreed to have regular intercourse with the intent of conception during the study . The primary outcome was live birth during the treatment period . RESULTS Women who received letrozole had more cumulative live births than those who received clomiphene ( 103 of 374 [ 27.5 % ] vs. 72 of 376 [ 19.1 % ] , P=0.007 ; rate ratio for live birth , 1.44 ; 95 % confidence interval , 1.10 to 1.87 ) without significant differences in overall congenital anomalies , though there were four major congenital anomalies in the letrozole group versus one in the clomiphene group ( P=0.65 ) . The cumulative ovulation rate was higher with letrozole than with clomiphene ( 834 of 1352 treatment cycles [ 61.7 % ] vs. 688 of 1425 treatment cycles [ 48.3 % ] , P<0.001 ) . There were no significant between-group differences in pregnancy loss ( 49 of 154 pregnancies in the letrozole group [ 31.8 % ] and 30 of 103 pregnancies in the clomiphene group [ 29.1 % ] ) or twin pregnancy ( 3.4 % and 7.4 % , respectively ) . Clomiphene was associated with a higher incidence of hot flushes , and letrozole was associated with higher incidences of fatigue and dizziness . Rates of other adverse events were similar in the two treatment groups . CONCLUSIONS As compared with clomiphene , letrozole was associated with higher live-birth and ovulation rates among infertile women with the polycystic ovary syndrome . ( Funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and others ; Clinical Trials.gov number , NCT00719186 . ) OBJECTIVE To compare the use of an aromatase inhibitor ( letrozole ) with the use of clomiphene citrate ( CC ) . DESIGN Prospect i ve r and omized study . SETTING An infertility clinic in a university hospital . PATIENT(S ) Seventy-four consecutive infertile patients with polycystic ovary syndrome were recruited . Thirty-eight patients were r and omized to the letrozole group ( 99 cycles ) , and the remaining patients were recruited to the CC group ( 95 cycles ) . INTERVENTION(S ) The aromatase inhibitor letrozole ( 2.5 mg/d ) and CC ( 100 mg/d ) were administered orally on days 3 - 7 of menses . MAIN OUTCOME MEASURE(S ) Number of follicles , endometrial thickness , E(2 ) levels on hCG day , and pregnancy rates among both groups . RESULT ( S ) Ovulation occurred in 65.7 % ( 65/99 ) of letrozole cycles and in 74.7 % ( 71/95 ) of CC cycles . The median ( minimum-maximum ) number of follicles sized > 15 mm in diameter on the day of hCG administration were 1 ( 0 - 4 ) and 1 ( 0 - 5 ) in the letrozole and CC groups , respectively . On the day of hCG administration , median serum E(2 ) concentrations in the letrozole and CC groups were statistically significantly different : 189 pg/mL ( 18 - 1,581 pg/mL ) and 386 pg/mL ( 27 - 6,190 pg/mL ) , respectively . The median serum E(2 ) concentrations per follicle sized > 15 mm in diameter on the day of hCG also statistically significantly differed between the letrozole and CC groups : 160 pg/mL ( 18 - 808 pg/mL ) and 281 pg/mL ( 27 - 2,615 pg/mL ) , respectively . The median endometrial thickness on the day of hCG did not significantly differ between the CC and letrozole groups ; it was 8 mm . Pregnancy was achieved in nine cycles ( 9.1 % ) of the letrozole group and in seven cycles ( 7.4 % ) of the CC group , which also was not a statistically significant difference . CONCLUSION ( S ) The aromatase inhibitor letrozole may be an acceptable alternative to CC as an ovulation-induction drug in patients with PCOS OBJECTIVE To compare the effect of letrozole with combined metformin and clomiphene citrate ( CC ) for ovulation induction in CC-resistant women with polycystic ovary syndrome ( PCOS ) . DESIGN A r and omized controlled trial . SETTING University teaching hospital and a private practice setting . PATIENT(S ) Two hundred fifty anovulatory women ( 582 cycles ) with CC-resistant PCOS . INTERVENTION(S ) Patients received 2.5 mg of letrozole daily ( 123 patients , 285 cycles ) or combined metformin-CC ( 127 patients , 297 cycles ) for three treatment cycles . MAIN OUTCOME MEASURE(S ) Ovulation rate , number of follicles , serum E(2 ) , serum P , endometrial thickness , pregnancy , and miscarriage rates . RESULT ( S ) Ovulation occurred in 185/285 cycles ( 64.9 % ) in the letrozole group versus 207/297 cycles ( 69.6 % ) in the combined metformin-CC group , without statistically significant difference . The total number of follicles was significantly more in the combined metformin-CC group ( 4.4+/-0.4 vs. 6.8+/-0.3 ) . A nonsignificant increase in endometrial thickness on the day of hCG administration was observed in the letrozole group ( 9.5+/-0.2 mm vs. 9.1+/-0.1 mm ) . No statistically significant difference regarding the pregnancy rate ( PR ) was observed between both groups ( 14.7 % vs. 14.4 % ) . CONCLUSION ( S ) Letrozole and combined metformin-CC are equally effective for inducing ovulation and achieving pregnancy in patients with CC-resistant PCOS Purpose This study is design ed to evaluate and compare follicular phase parameters during ovarian stimulation with the clomiphene citrate ( CC ) and letrozole ( LET ) in unexplained infertile patients who failed to get pregnant following frequent CC-treated cycles . Methods A total of 64 unexplained infertile women who failed to get pregnant following frequent CC-treated cycles were studied for one CC-treated cycle ( 100 mg/day ) , 2 washout cycles , and then 1 LET-treated cycle ( 5 mg/day ) . Number of follicles over 14 mm in diameter , diameter of the largest follicles , endometrial thickness , serum estradiol ( E2 ) and LH levels were measured when one mature follicle over 18 mm in diameter detected during transvaginal ultrasonography . Results The mean value of the largest follicle diameter , number of developed follicles > 14 mm , endometrial thickness and LH in LET-treated cycle was significantly higher than CC-treated cycle ( P values were 0.007 , < 0.001 , < 0.001 , and 0.004 , respectively ) , whereas mean level of E2 showed a significantly lower level during LET-treated cycle ( P < 0.001 ) . Conclusions About 5 mg/day of LET is associated with better follicular phase parameters , endometrial development , serum E2 and LH levels in women with unexplained infertility who failed to get pregnant following frequent CC-treated cycles Letrozole was compared with clomiphene citrate ( CC ) as a first-line treatment for ovulation induction in women with polycystic ovaries ( PCOs ) . A total of 106 women with primary infertility and a diagnosis of PCOs were r and omized to receive either 100 mg CC ( n = 55 ) or 2.5 mg letrozole ( n = 51 ) daily for 5 days . Human chorionic gonadotrophin ( hCG ) at a dose of 10 000 IU was administered when at least one follicle with a mean diameter ≥ 18 mm was observed 
    Output:
    
The reasons for downgrading the evidence were poor reporting of study methods , possible publication bias and the tendency for studies that reported live birth to report higher clinical pregnancy rates in the letrozole group than studies that failed to report live birth ( suggesting that results might be somewhat less favourable to letrozole if all studies reported live birth ) .
Letrozole appears to improve live birth and pregnancy rates in subfertile women with anovulatory PCOS , compared to clomiphene citrate .
OHSS was a very rare event , with no occurrences in most studies