title: Factors predicting double embryo implantation following double embryo transfer in assisted reproductive technology: implications for elective single embryo transfer.
abstract: OBJECTIVE
  The aim of this study was to identify factors associated with double embryo implantation following double embryo transfer (DET) during assisted reproductive technology (ART) procedures and to evaluate the implications of findings in selecting candidates for elective single embryo transfer (eSET).
  
  
  METHODS
  Factors predicting double embryo implantation, defined as embryo transfers with two or more heartbeats on 6-week ultrasound following DET, were assessed using the US National ART Surveillance System data from 2000 to 2012 (n = 1,793,067 fresh, autologous transfers). Adjusted risk ratios (aRRs) were estimated after stratifying by prognosis. Favorable prognosis was defined as first-time ART with supernumerary embryo(s) cryopreserved. Average prognosis was defined as first-time ART without supernumerary embryo(s) cryopreserved, prior unsuccessful ART with supernumerary embryo(s) cryopreserved, or prior ART with previous birth(s) conceived with ART or naturally. Rates and factors associated with double embryo implantation were compared with single embryo implantation following DET among both prognosis groups.
  
  
  RESULTS
  Double embryo implantation was positively associated with blastocyst (versus cleavage) transfer in favorable (aRR = 1.58 (1.51-1.65)) and average (aRR = 1.67 (1.60-1.75)) prognosis groups and negatively associated with age >35 years in both prognosis groups. For average prognosis patients, double embryo implantation was associated with retrieving >10 oocytes (aRR = 1.22 (1.18-1.24)).
  
  
  CONCLUSIONS
  Regardless of prognosis, patients aged <35 years with blastocyst-stage embryos and average prognosis patients from whom >10 oocytes were retrieved may be good candidates for eSET. Physicians may consider using these data to counsel patients on eSET, which would reduce multiple gestations and associated complications.
authors.affiliation: Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-74, Atlanta, GA, 30341, USA. Caitlin.Martin@emory.edu.|Department of Gynecology and Obstetrics, Emory University, Glenn Building, 4th Floor, 69 Jesse Hill Jr Drive SE, Atlanta, GA, 30303, USA. Caitlin.Martin@emory.edu.
authors.forename: Caitlin
authors.identifier: http://orcid.org/0000-0003-3073-2467
authors.initials: C
authors.lastname: Martin
authors.affiliation: Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-74, Atlanta, GA, 30341, USA.
authors.forename: Jeani
authors.initials: J
authors.lastname: Chang
authors.affiliation: Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-74, Atlanta, GA, 30341, USA.
authors.forename: Sheree
authors.initials: S
authors.lastname: Boulet
authors.affiliation: Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-74, Atlanta, GA, 30341, USA.
authors.forename: Denise J
authors.initials: DJ
authors.lastname: Jamieson
authors.affiliation: Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Mailstop F-74, Atlanta, GA, 30341, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Kissin
mesh_terms: D000328:Adult; D000367:Age Factors; D001755:Blastocyst / Q000502:physiology; D015925:Cryopreservation / Q000379:methods*; D010064:Embryo Implantation / Q000502:physiology*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D011247:Pregnancy; D011272:Pregnancy, Multiple; D047928:Premature Birth; D027724:Reproductive Techniques, Assisted; D056826:Single Embryo Transfer / Q000379:methods*
keywords: Double embryo implantation; Double embryo transfer; Elective single embryo transfer; In vitro fertilization; Multiple birth pregnancy