A Cochrane review [Abstract] 1 included 60 479 women in 115 trials, most of which were conducted in China. Mid-dose mifepristone (25-50 mg) (RR 0.61, 95% CI 0.45 to 0.83; 27 trials, n=6052) or low-dose mifepristone (< 25 mg) (RR 0.72, 95% CI 0.52 to 0.99; 14 trials, n=8752) were significantly more effective than levonorgestrel (LNG), but the significance was marginal when only high-quality studies were included (RR 0.70, 95% CI 0.49 to 1.01; 4 trials). Mid-dose mifepristone was associated with fewer pregnancies than low-dose mifepristone (RR 0.73, 95% CI 0.55 to 0.97; 25 RCTs, n=11 914). Ulipristal acetate (UPA) appeared more effective than LNG at a marginal level within 72 hours of intercourse (RR 0.59, 95% CI 0.35 to 0.99; 2 RCTs, n=3 448). Single-dose LNG (1.5 mg) showed similar effectiveness as the two-dose regimen (0.75 mg 12 h apart) (RR 0.84, 95% CI 0.53 to 1.33; 3 trials, n=6653). LNG taken within 72 hours of intercourse was more effective than LNG taken after 72 hours (RR 0.51, 95% CI 0.31 to 0.84; 4 trials, n=7453). It was not evident that the coitus-treatment time affected the effectiveness of mifepristone and UPA. There was no conclusive evidence of a difference in the risk of pregnancy between the Cu-IUD and mifepristone (RR 0.33, 95% CI 0.04 to 2.74; 2 RCTs, n=395, low-quality evidence). Levonorgestrel and mifepristone were associated with fewer pregnancies than Yuzpe (estradiol-levonorgestrel combination) (RR 0.57, 95% CI 0.39 to 0.84; 6 RCTs, n=4 750 and RR 0.14, 95% CI 0.05 to 0.41; 3 RCTs, n=2 144, respectively).
An RCT 3 including 860 women assessed whether a single 40 mg oral dose of piroxicam as co-treatment with LNG improved emergency contraceptive efficacy. One (0.2%) of 418 efficacy-eligible women in the piroxicam group were pregnant, compared with 7 (1.7%) of 418 in the placebo group (odds ratio 0.20, 95% CI 0.02 to 0.91; p=0.036). LNG plus piroxicam prevented 94.7% of expected pregnancies compared with 63.4% for LNG plus placebo.
A study 2 reviewing data from 6873 women in 4 WHO-HRP randomized trials evaluated the effect of increased body weight and BMI on pregnancy rates with LNG 1.5mg used as emergency contraception. Overall pregnancy rate was low at 1.2%. Pregnancy rates were also low in women weighing over 80kg (0.7%) and who were obese (BMI over 30) (2.0%). The pooled analyses demonstrated that BMI over 30 decreased efficacy significantly (odds ratio 8.27, 95% CI 2.70 to 25.37) when compared to women in lower BMI categories, mainly influenced by pregnancies in obese women from one study site. Sensitivity analyses excluding that site showed that obesity was no longer a risk factor; however, the other studies included too few obese women in the sample to exclude a substantial decrease in efficacy.
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