Levonorgestrel emergency contraception and bodyweight: are current recommendations consistent with historic data?

To assess the consistency between current recommendations that women of body weight (BW) or body mass index (BMI) above a defined threshold should use a double dose of levonorgestrel (LNG) for emergency contraception (EC) and observed frequency of pregnancy in historic studies of single-dose LNG for EC. We applied double dose recommendation criteria to individual participant level data from three historic studies of the WHO's Human Reproductive Program to categorize subjects into single dose-recommended (SDR) and double dose-recommended (DDR) groups and compared the latter to the former using pregnancy risk ratios (RR). A total of 5859 subjects with 59 pregnancies made up the full dataset. Depending on the recommendation source (USA or UK) and inclusion or exclusion of heavy outlier data, DDR criteria were satisfied by 3.7% to 18.9% of subjects. Pregnancy proportions were mostly lower in DDR than in SDR subjects, with risk ratio estimates ranging from zero to 1.17, exceeding unity only when the USA criterion was used with outliers included. DDR subjects had a significantly lower relative frequency of pregnancy than SDR subjects when the UK criteria were used and outliers excluded (RR = 0.17 [95% CI: 0.04; 0.70],  = .0024). Our findings are consistent with the notion that there is no real loss of pregnancy control with single-dose LNG-EC in high-BMI and/or high-BW users, and today's double dose recommendations were prematurely issued and remain questionable.