title: Multiple gestations in assisted reproductive technology: can they be avoided with blastocyst transfers?
abstract: OBJECTIVE
  Blastocysts are advanced-stage embryos with high implantation potential; theoretically, limited numbers of blastocysts can be used for embryo transfer to achieve good pregnancy rates with low multiple pregnancy rates. Clinical outcomes of a newly implemented blastocyst transfer program were evaluated.
  
  
  METHODS
  This study is a retrospective analysis of 553 blastocyst transfer cycles performed by a university-based in vitro fertilization program; risk factors associated with multiple gestations were analyzed.
  
  
  RESULTS
  An average of 2.2 embryos were used for embryo transfer. The overall clinical pregnancy rate per embryo transfer was 45.1%; multiple gestation, twin, and triplet rates were 40.9%, 36.5%, and 4.3%, respectively. Multiple gestations increased significantly (1) when embryo transfer was done on day 5, (2) when > or =2 blastocysts were present on day 5, and (3) when maternal age was < or =30 years.
  
  
  CONCLUSIONS
  In spite of a conservative approach to the number of blastocysts used for embryo transfer, the overall multiple pregnancy rate was high, and triplet pregnancies did occur.
authors.affiliation: Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, Oregon Health Sciences University, Portland, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gorrill
authors.forename: K
authors.initials: K
authors.lastname: Sadler-Fredd
authors.forename: P E
authors.initials: PE
authors.lastname: Patton
authors.forename: K A
authors.initials: KA
authors.lastname: Burry
mesh_terms: D001755:Blastocyst; D004624:Embryo Transfer / Q000379:methods; D005260:Female; D006801:Humans; D008423:Maternal Age; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data; D012099:Reproductive Techniques / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D014310:Triplets / Q000706:statistics & numerical data; D014427:Twins / Q000706:statistics & numerical data