A well-designed pharmacokinetics (PK) study may identify the physiologic basis for observed differences in levonorgestrel emergency contraception (LNG-EC) and ulipristal acetate emergency contraception (UPA-EC) failure rates in women with normal and obese BMI. The investigators propose a study to compare serum LNG and UPA levels after administration of a single-dose of LNG-EC or UPA-EC. The investigators hypothesize that there will be no difference in PK parameters between women with normal BMI and obese women.