Data analysis
UHPLC-MS/MS data collection and analysis were performed using MassLynx 4.2 (Waters Corporation). The ratio of the analyte peak area to internal standard peak area was determined for all the calibration curve samples, internal quality controls (IQCs) and serum samples. While the peak area of MPA-d6 or NET-d6 was used to quantify MPA or NET, respectively, the mean peak area of MPA-d6 and NET-d6 was used for the quantification of LNG, ETG, NES and GES.The analysis of unimputed data used only observed concentrations higher than the LLOQ. In other words, only the participants with quantifiable levels are included in this analysis. For imputed data, values between the LLOQ and the limit of detection (LOD) were assigned 0.5 x LLOQ, while values lower than LOD were assigned as 0.000. For the imputed data, all participants were included in the data analysis.We performed modified intention-to-treat (mITT) and per protocol (PP) analyses (PP1 and PP2). For the PP1 analysis, to obtain the most robust study progestin peak serum values at 25W, we excluded participants that did not receive their 24W injection (DMPA-IM n = 7; NET-EN n = 3) and those that had a concentration of non-study progestins greater than its LLOQ at 25W (DMPA-IM n = 47; NET-EN n = 62). For the PP2 analysis, to investigate associations between progestin concentrations, weight and BMI, we excluded participants that did not receive their 24W injection (DMPA-IM n = 7; NET-EN n = 3) and those with non-study serum progestin concentrations greater than 1.5 nM, at both D0 and 25W (DMPA-IM n = 27; NET-EN n = 66).Differences in baseline characteristics between arms were assessed using Pearson’s chi-squared or Fisher’s exact test, where applicable, or a two-sample t-test (for differences in age) and a Wilcoxon rank-sum test (for differences in weight and BMI).Progestin results were analysed using GraphPad Prism 9.31 from GraphPad Software, Inc. (La Jolla California, USA) and SAS 9.4 (SAS Institute Inc., Cary, USA). All data in the main text, unless otherwise indicated, are expressed as median with interquartile range (IQR). For some tables, data are expressed as median with minimum and maximum values, to highlight outliers. Means with minimum and maximum values are also given for some of the data, where thought to be informative (