title: What is a preclinical pregnancy loss?
abstract: OBJECTIVE
  To evaluate the contribution of embryo quality to preclinical loss rates after in vitro fertilization (IVF)/embryo transfer (ET) pregnancy, multiple gestation, and clinical loss rates were compared to preclinical pregnancy loss rates over a 3-year period.
  
  
  METHODS
  The pregnancy outcomes after 1675 fresh ETs from 1994 to 1997 were studied. While establishment of a clinical pregnancy confirms uterine receptivity, multiple gestation rates reflect embryo quality. Because the majority of clinical losses are chromosomally abnormal, clinical loss rates serve as another indicator of embryo quality.
  
  
  RESULTS
  The overall preclinical pregnancy loss rate was 5% (78/1675) of ETs and 17% (78/472) of pregnancies. During the 3-year period the pregnancy rates per ET increased from 19 to 36% (P < 0.0001), multiple gestation rates increased from 21 to 48% (P < 0.008), clinical loss rates decreased from 20 to 6% (P < 0.0001), and preclinical pregnancy loss rates remained unchanged from 13 to 19% (P = 0.1).
  
  
  CONCLUSIONS
  Preclinical pregnancy loss more likely reflects abnormalities in uterine receptivity rather than embryo quality. If recurrent preclinical pregnancy loss occurs after IVF/ET, evaluation for abnormalities of uterine receptivity should be performed.
authors.affiliation: Center of Human Reproduction, Chicago, Illinois 60610, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Coulam
authors.forename: C
authors.initials: C
authors.lastname: Chapman
authors.forename: J S
authors.initials: JS
authors.lastname: Rinehart
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology / Q000503:physiopathology; D002869:Chromosome Aberrations / Q000235:genetics; D025063:Chromosome Disorders; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D018873:Pregnancy Rate; D014599:Uterus / Q000502:physiology