Representative UPLC-MS/MS chromatograms of sex-steroid hormones spiked to double stripped human serum. (A) progestogens at 1,000 pg/ml and internal standard testosterone-d3 at 400 pg/ml, (B) progestogens at LLOQs (25 pg/ml), (C) estrogens at 100 pg/ml and internal standard estradiol-d5 at 25 pg/ml, (D) estrogens at LLOQs (2.5 and 5.0 pg/ml for estradiol and ethinyl estradiol, respectively).