Assessment of risk of bias for the 18 studies included in the individual participant data meta-analysis.

aImportant confounders include pregnancy status, coital frequency, marital status/living with partner, transactional sex; “yes” indicates all measured; “no” indicates one or more missing.
bLower risk of bias based on “yes” to all: ≥80% followed at 12 mo, measurement of important confounders, contraceptive method measured every 3 mo or more frequently, and ≥10% in no-HC comparison group.
cFollow-up visits every 6 mo.
Assessment of risk of bias for the 18 studies included in the individual participant data meta-analysis.