Assessment of bias: measures of the studies included in the analysis.

areferences for first three summary measures provided in Table 1; references for the last two summary measures footnoted here:b[10], [12], [14], [15], [17], [24]–[27], [29], [45]–[54], [57], [58], [60], [75], [77]–[88],c[7], [13], [16], [42]–[44], [59],d[18], [35]–[41].e[30], [55].Key: HC = hormonal contraception, combined = combined oestrogen- and progesterone-containing methods of HC, POC = progesterone only containing methods of HC.