Serum concentrations of selected PFAS with detection rates >70% by parity status (nulliparous or parous) in women (n=75) across the United States for four SWAN visits. Boxes represent the 25th-75th percentiles, horizontal lines represent the median, and whiskers indicate 5th and 95th percentiles, respectively. Repeated measure analysis of variance tests was conducted to compare temporal variations of PFAS concentrations by parity group: P=0.03 for n-PFOA; P=0.03 for n-PFOS; P=0.19 for sm-PFOS; P=0.99 for PFHxS; P=0.28 for PFNA. Note that a log scale is used for Y axis. The limits of detection were 0.1 ng/mL for all PFAS analytes. Abbreviations: n-PFOA, linear-chain perfluorooctanoic acid; PFNA, perfluorononanoic acid; PFHxS, perfluorohexane sulfonic acid; n-PFOS, linear-chain perfluorooctane sulfonic acid; sm-PFOS, sum of branched-chain perfluorooctane sulfonic acid.