【Objective】 To compare the effect of different GnRHa downregulation long protocols on the synchronization of follicular development and IVF outcomes. 【Methods】 A total of 859 cycles of long protocol IVF/ ICSI were analyzed retrospectively and divided into four groups: Group A (174 cycles): patients received shortacting GnRHa 0.1 mg every other day starting from day 20 of the previous cycle

after 14 days the dosage was changed to 0.1 mg /day and continued until the day HCG was administered. Group B (77 cycles):patients received shortacting GnRHa 0.1 mg/d starting from day 20 of the previous cycle till the day HCG was administered; Group C (323 cycles) : patients received a single depot injection of GnRHa 0.75 mg on day 20 of the previous cycle; Group D (285 cycles) : patients received a single depot injection of GnRHa 0.93 mg on day 20 of the previous cycle. Serum FSH and LH levels on day 1 of gonadotropin stimulation

the number of >14 mm follicles on HCG day and the number of oocytes retrieved

high quality embryos rate

clinical pregnancy rate and implantation rate were compared respectively.【Results】 After downregulation for 14days

 serum FSH (4.51 ± 1.61) IU/L and LH levels (2.64 ± 1.45) IU/L were much higher in group A than in other groups (4.04 ± 1.21

2.27 ± 1.55; 2.79 ± 1.44

2.13 ± 1.03; 2.69 ± 1.26

2.02 ± 0.96) IU/L

the differences were statistically significant (P < 0.05). On the day of HCG was administered

there were more > 14 mm follicles in group A (7.95 ± 3.49

55.43%) than others (9.18 ± 4.09

66.62%; 9.6 ± 4.17

59.67%; 10.43 ± 4.41

66.73%). Patients in group A required more days of gonadotropin stimulation (9.78 ± 1.51; 10.81 ± 1.93; 11.16 ± 1.98; 11.4 ± 2.12) days

but with less oocytes retrieved (10.38 ± 4.68; 12.17 ± 5.29; 12.97 ± 5.29; 13.59 ± 5.41)

mature oocytes (8.91 ± 4.1; 10.25 ± 4.58; 11.36 ± 4.92; 11.95 ± 5.02) and embryos available (5.7 ± 3.05; 5.97 ± 3.47; 7.35 ± 4.12; 7.89 ± 4.0). Clinical pregnancy rate and implantation rate were lower in group A (49.42%

32.99%) than in other groups (55.84%

39.39%; 57.59%

37.82%; 60%

41.22%)

the differences were statistically significant (P < 0.05).【Conclusions】 Shortacting GnRHa administered every other day is not effective on the control of pituitary downregulation

and therefore may reduce the number of follicles recruited. Moreover

serum LH stay higher after downregulation

and this may affect the synchronization of follicular development and IVF outcomes.