Study characteristics
Study characteristics were showed in Table 1 . Eighteen studies used TA alone (30, 32, 33, 43-46, 51-53, 58, 61, 62, 64, 67, 74, 75, 77), 6 studies involved the administration of WA alone (59, 60, 66, 70, 71, 73), 6 for EA alone (7, 39, 49, 50, 63, 76), 5 for TEAS alone (33, 34, 37, 38, 41) and the remaining fourteen studies had two treatment groups or combined with two interventions in a treatment group. Only sham or placebo acupuncture was administered in 11 studies (30, 33, 38, 41, 43, 44, 46, 51, 53, 54, 70), and 24 studies used only a no treatment control (7, 25, 31, 32, 34, 39, 45, 47, 49, 50, 52, 58-63, 65, 66, 71-73, 75, 76 ). Ten trials included three arms (31, 40, 41, 48, 52, 54, 63, 64, 74, 77) and 4 trials were four-arms (34, 35, 37, 67). Among them, both sham control and no treatment control were used in 5 trials (35, 40, 64, 74, 77). Seven studies included women who were RIF patients (33, 38, 40, 61, 65, 66, 71). Acupuncture was provided before the ET among 8 studies and 20 studies around the ET. The acupuncture sessions differed across studies. Regarding TA treatment, 2 studies performed one acupuncture session, 17 studies performed two acupuncture sessions and 9 studies performed three or above sessions. CPR was available from all the 49 trials. 13 reported LBR (30, 32-35, 38, 41, 43-46, 50, 60, 74) and 10 studies provided OPR data (31, 32, 39, 43, 44, 46, 51-53, 56). 27 studies were performed in China (33, 34, 37, 38, 41, 44, 46, 49, 55-74, 76, 77), 9 in Europe (7, 35, 43, 51, 52, 54-56, 75), 4 in USA (42, 47, 48, 50), and the remaining were in other country. The main objective in 4 studies was to assess pain relief (7, 54-56), and the remaining studies were all for improvement of IVF outcomes. Total samples sizes for each study ranged from 44 to 848 women.