title: Single vitrified blastocyst transfer maximizes liveborn children per embryo while minimizing preterm birth.
abstract: OBJECTIVE
  To compare live-birth rates, blastocyst to live-birth efficiency, gestational age, and birth weights in a large cohort of patients undergoing single versus double thawed blastocyst transfer.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  Assisted reproduction technology (ART) practice.
  
  
  METHODS
  All autologous frozen blastocyst transfers (FBT) of one or two vitrified-warmed blastocysts from January 2009 through April 2012.
  
  
  METHODS
  Single or double FBT.
  
  
  METHODS
  Live birth, blastocyst to live-birth efficiency, preterm birth, low birth weight.
  
  
  RESULTS
  Only supernumerary blastocysts with good morphology (grade BB or better) were vitrified, and 1,696 FBTs were analyzed. No differences were observed in patient age, rate of embryo progression, or postthaw blastomere survival. Double FBT yielded a higher live birth per transfer, but 33% of births from double FBT were twins versus only 0.6% of single FBT. Double FBT was associated with statistically significant increases in preterm birth and low birth weight, the latter of which was statistically significant even when the analysis was limited to singletons. Of the blastocysts transferred via single FBT, 38% resulted in a liveborn child versus only 34% with double FBT. This suggests that two single FBTs would result in more liveborn children with significantly fewer preterm births when compared with double FBT.
  
  
  CONCLUSIONS
  Single FBT greatly decreased multiple and preterm birth risk while providing excellent live-birth rates. Patients should be counseled that a greater overall number of live born children per couple can be expected when thawed blastocysts are transferred one at a time.
authors: Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Rockville, Maryland; Shady Grove Fertility Reproductive Science Center, Washington, District of Columbia; Shady Grove Fertility Reproductive Science Center, Rockville, Maryland. Electronic address: kate.devine@nih.gov.
authors: Kate
authors: K
authors: Devine
authors: Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Rockville, Maryland.
authors: Matthew T
authors: MT
authors: Connell
authors: Shady Grove Fertility Reproductive Science Center, Washington, District of Columbia; Shady Grove Fertility Reproductive Science Center, Rockville, Maryland.
authors: Kevin S
authors: KS
authors: Richter
authors: Department of Obstetrics and Gynecology, Walter Reed National Military Medical Center, Bethesda, Maryland.
authors: Christina I
authors: CI
authors: Ramirez
authors: Shady Grove Fertility Reproductive Science Center, Washington, District of Columbia; Shady Grove Fertility Reproductive Science Center, Rockville, Maryland.
authors: Eric D
authors: ED
authors: Levens
authors: Program in Reproductive and Adult Endocrinology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Rockville, Maryland.
authors: Alan H
authors: AH
authors: DeCherney
authors: Shady Grove Fertility Reproductive Science Center, Washington, District of Columbia; Shady Grove Fertility Reproductive Science Center, Rockville, Maryland.
authors: Robert J
authors: RJ
authors: Stillman
authors: Shady Grove Fertility Reproductive Science Center, Washington, District of Columbia; Shady Grove Fertility Reproductive Science Center, Rockville, Maryland.
authors: Eric A
authors: EA
authors: Widra
mesh_terms: D000328:Adult; D017677:Age Distribution; D015331:Cohort Studies; D015925:Cryopreservation / Q000706:statistics & numerical data; D046149:Embryo Culture Techniques / Q000379:methods / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000379:methods / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D050498:Live Birth / Q000453:epidemiology*; D008396:Maryland / Q000453:epidemiology; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology* / Q000517:prevention & control*; D012189:Retrospective Studies; D012307:Risk Factors; D016896:Treatment Outcome; D014427:Twins / Q000706:statistics & numerical data*
keywords: Frozen embryo transfer; low birth weight; preterm birth; single embryo transfer; vitrification