title: Selection bias in in vitro fertilization programs.
abstract: Pregnancy rates per cycle reported from different in vitro fertilization-embryo transfer programs vary widely. While several programs have reported constant pregnancy rates per cycle, others report declining pregnancy  rates. Selection biases at the point of entry and between cycles are discussed as possible explanations of these discrepancies.
authors.affiliation: Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: A
authors.initials: A
authors.lastname: Hershlag
authors.forename: E H
authors.initials: EH
authors.lastname: Kaplan
authors.forename: R A
authors.initials: RA
authors.lastname: Loy
authors.forename: A H
authors.initials: AH
authors.lastname: DeCherney
authors.forename: G
authors.initials: G
authors.lastname: Lavy
mesh_terms: D015982:Bias; D004608:Eligibility Determination; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008297:Male; D011247:Pregnancy