Fig. 1.

Flowchart of participant selection. Among 33,944 participants who were interviewed in NHANES III in 1988–1994, 14,797 adults aged 20–74 completed adult questionnaire (AQ) and received physical examinations at the mobile examination center (MEC) where blood samples collection and a gallbladder ultrasonography were also performed. In the current analysis, we included 4338 females aged 20–60 who reported their history of oral contraceptive pills use and had the last menstrual period (LMP) within the prior 12 months. Women without any of the following anthropometric measures were excluded: body mass index, waist circumference or waist-to-hip ratio