title: Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception.
abstract: OBJECTIVE
  To further evaluate the effect of weight and body mass index (BMI) on the efficacy of levonorgestrel emergency contraception.
  
  
  METHODS
  Data from two large, multicenter, randomized controlled trials designed to assess emergency contraceptive efficacy were pooled to evaluate the effect of weight and BMI on pregnancy rates among women who received levonorgestrel. Descriptive methods (comparison of means and distributions according to pregnancy status and pregnancy rates across weight and BMI categories) as well as cubic spline modeling were used to describe the relationship between pregnancy risk and weight/BMI.
  
  
  RESULTS
  The analysis population comprised 1731 women, among whom 38 pregnancies were reported. Women for whom levonorgestrel was not effective in preventing pregnancy had a significantly higher mean body weight and BMI than women who did not become pregnant (76.7 vs. 66.4 kg, p<.0001; 28.1 vs. 24.6 kg/m², p<.0001). The estimated pregnancy rate increased significantly from 1.4% [95% confidence interval (CI): 0.5%-3.0%] among the group of women weighing 65-75 kg to 6.4% (95% CI: 3.1%-11.5%) and 5.7% (95% CI: 2.9%-10.0%) in the 75-85 kg and >85 kg groups, respectively. Statistical modeling demonstrated a steep increase in pregnancy risk starting from a weight near 70-75 kg to reach a risk of pregnancy of 6% or greater around 80 kg. Similar results were obtained for statistical modeling of BMI as well as when the two studies were analyzed individually.
  
  
  CONCLUSIONS
  All analyses showed a significant drop in the efficacy of levonorgestrel emergency contraception with increasing body weight, with pregnancy risk in the higher weight categories similar to expected rates in the absence of contraception. Like body weight, increasing BMI was highly correlated with increased pregnancy risk.
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France. Electronic address: n.kapp@hra-pharma.com.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Kapp
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: Jean Louis
authors.initials: JL
authors.lastname: Abitbol
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: Henri
authors.initials: H
authors.lastname: Mathé
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Scherrer
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Guillard
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: Erin
authors.initials: E
authors.lastname: Gainer
authors.affiliation: HRA Pharma, 15 rue Béranger, 75003 Paris, France.
authors.forename: André
authors.initials: A
authors.lastname: Ulmann
mesh_terms: D015992:Body Mass Index; D001835:Body Weight; D003281:Contraceptives, Postcoital / Q000008:administration & dosage; D004334:Drug Administration Schedule; D004351:Drug Resistance; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D016912:Levonorgestrel / Q000008:administration & dosage; D008954:Models, Biological; D050177:Overweight / Q000378:metabolism*; D011247:Pregnancy; D018873:Pregnancy Rate; D011275:Pregnancy, Unwanted; D012306:Risk; D006113:United Kingdom / Q000453:epidemiology; D014481:United States / Q000453:epidemiology
chemical_list: D003281:Contraceptives, Postcoital; D016912:Levonorgestrel
keywords: Body mass index; Body weight; Efficacy; Emergency contraception; Hormonal contraception; Levonorgestrel