title: Factors affecting success rates in two concurrent clinical IVF trials: an examination of potential explanations for the difference in pregnancy rates between the United States and Europe.
abstract: OBJECTIVE
  To compare a US clinical trial of gonadotropin therapy for IVF with a similar European trial to determine what factors may explain the higher clinical pregnancy rate in the US trial.
  
  
  METHODS
  Comparison of baseline, treatment, and outcome variables in the United States (US) and European trials.
  
  
  METHODS
  IVF practices in the US (n=4) and Europe (n=6).
  
  
  METHODS
  297 women undergoing IVF.
  
  
  METHODS
  None.
  
  
  METHODS
  Clinical pregnancy rate.
  
  
  RESULTS
  Clinical pregnancy rates were 43.4% in the US compared with 29.7% in Europe (p=0.016), with a live birth rate of 38.2% versus 27.6% (p=0.064). This difference in clinical pregnancy rate could not be explained by differences in the US versus Europe for number of embryos transferred (2.3 vs. 2.6) or female age (34.6 vs. 30.4). Although the starting dose of gonadotropin was higher in the US trial compared with the European trial (300 versus 225 IU), the total dose of gonadotropin was only slightly higher in the US. In multiple logistic regression analysis of 81 pretransfer variables on clinical pregnancy, the only two found to be significant predictors of outcome were baseline endometrial thickness following down-regulation and number of days of gonadotropin treatment.
  
  
  CONCLUSIONS
  This study suggests the possibility that US pregnancy rates may be higher in part because of differences in down-regulation or gonadotropin dosing. Other factors not assessed in these studies or in national datasets likely also contribute to the difference in pregnancy rates.
authors.affiliation: Department of Obstetrics and Gynecology, Stanford University Medical Center, Stanford, California. Electronic address: vlbaker@stanford.edu.
authors.forename: Valerie L
authors.initials: VL
authors.lastname: Baker
authors.affiliation: Institut Biochimique SA (IBSA), Lugano, Switzerland.
authors.forename: Clarence E
authors.initials: CE
authors.lastname: Jones
authors.affiliation: Institut Biochimique SA (IBSA), Lugano, Switzerland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Cometti
authors.affiliation: Biostatistician Consultant, Orange, California.
authors.forename: Fred
authors.initials: F
authors.lastname: Hoehler
authors.affiliation: Medecine de la Reproduction, Hôpital Femme Mère Enfants, Bron, France, Université Claude Bernard, Lyon, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Salle
authors.affiliation: Semmelweis University, first Department of OB/GYN, Division of Assisted Reproduction, Department of Obstetrics and Gynaecology, Budapest, Hungary.
authors.forename: János
authors.initials: J
authors.lastname: Urbancsek
authors.affiliation: Seattle Reproductive Medicine, Seattle, Washington.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Soules
mesh_terms: D000293:Adolescent; D000328:Adult; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000379:methods / Q000706:statistics & numerical data; D015981:Epidemiologic Factors; D005060:Europe / Q000453:epidemiology; D005260:Female; D005300:Fertility Agents, Female / Q000627:therapeutic use; D005307:Fertilization in Vitro / Q000706:statistics & numerical data*; D006062:Gonadotropins / Q000627:therapeutic use; D006801:Humans; D007246:Infertility / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy*; D008596:Menotropins / Q000627:therapeutic use; D011247:Pregnancy; D018873:Pregnancy Rate; D011379:Prognosis; D011994:Recombinant Proteins / Q000627:therapeutic use; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology; D055815:Young Adult
chemical_list: D005300:Fertility Agents, Female; D006062:Gonadotropins; D011994:Recombinant Proteins; D008596:Menotropins