title: Factors affecting occurrence of twin pregnancy after double embryo transfer on day 3.
abstract: OBJECTIVE
  The aim of this study was to identify the risk factors of twin gestation in fresh double day-3 embryo transfer cycles.
  
  
  METHODS
  Out of a total of 386 cycles of fresh double embryo transfers on day 3 between 2006 and 2013 at a single center, 72 women with single intrauterine gestational sac (GS) (single-GS group) and 32 women with double GS (double-GS group) were identified. The patients' clinical characteristics and laboratory results were extracted from electronic medical records and were compared.
  
  
  RESULTS
  The double-GS group had a significantly younger age (P = 0.012), and higher bodyweight (P = 0.033) compared with the single-GS group. The total number of blastomeres (P = 0.013) and cumulative embryo score (P = 0.012) were higher in the double-GS group. By receiver-operator curve analysis, maternal age ≤ 35 years, maternal bodyweight > 60 kg, total number of blastomeres > 14, and cumulative embryo score > 49 were the cut-off values to predict twin pregnancy. Among eight women with all four risk factors, the twin pregnancy rate was 87.5%. There was no twin pregnancy among seven women with no risk factors.
  
  
  CONCLUSIONS
  Younger age, higher bodyweight, and better embryo quality are all associated with a higher incidence of twin pregnancy after double embryo transfer on day 3. Single embryo transfer might be advisable for couples with risk factors for twin pregnancy.
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam.
authors.forename: Myo Sun
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul.
authors.forename: Ji Hee
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam.|Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Byung Chul
authors.initials: BC
authors.lastname: Jee
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam.|Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Chang Suk
authors.initials: CS
authors.lastname: Suh
authors.affiliation: Department of Obstetrics and Gynecology, Seoul National University Hospital, Seoul.|Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Seok Hyun
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000328:Adult; D001835:Body Weight; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D008423:Maternal Age; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012307:Risk Factors
keywords: double embryo transfer; in vitro fertilization; pregnancy; twins