title: Incidence of monozygotic twinning with blastocyst transfer compared to cleavage-stage transfer.
abstract: OBJECTIVE
  To evaluate the incidence of monozygotic twinning (MZT) in pregnancies conceived after blastocyst transfer compared to cleavage-stage transfer.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  University IVF program.
  
  
  METHODS
  All IVF patients with viable pregnancies conceived during a 4-year period.
  
  
  METHODS
  Blastocyst transfer or day 3 ET.
  
  
  METHODS
  Incidence of MZT assessed by transvaginal ultrasound.
  
  
  RESULTS
  There were 11 incidences of MZT in 197 viable pregnancies (5.6%) with blastocyst transfer compared to 7 of 357 viable pregnancies (2%) with day 3 ET. In 10 of 18 pregnancies, MZT was observed in the setting of a higher order multiple gestation (6 of 11 for blastocyst transfer and 4 of 7 for day 3 ET). In the day 3 ET group, assisted hatching or intracytoplasmic sperm injection (ICSI) did not increase MZT (4 of 213, 1.9%) compared to cycles without zona breaching (3 of 144, 2.1%). Similarly, in the blastocyst-transfer group, ICSI did not increase the incidence of MZT (4 of 74, 5.5% for ICSI and 7 of 123, 5.7% for non-ICSI IVF).
  
  
  CONCLUSIONS
  Compared to day 3 ET, blastocyst transfer appears to significantly increase the incidence of gestations with MZT. This information should be taken into account when counseling patients about the pros and cons of extended culture.
authors.affiliation: Department of Gynecology and Obstetrics, Stanford University School of Medicine, California 94305, USA. milki4@aol.com
authors.forename: Amin A
authors.initials: AA
authors.lastname: Milki
authors.forename: Sunny H
authors.initials: SH
authors.lastname: Jun
authors.forename: Mary D
authors.initials: MD
authors.lastname: Hinckley
authors.forename: Barry
authors.initials: B
authors.lastname: Behr
authors.forename: Linda C
authors.initials: LC
authors.lastname: Giudice
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Westphal
mesh_terms: D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D012189:Retrospective Studies; D020554:Sperm Injections, Intracytoplasmic; D014430:Twins, Monozygotic / Q000706:statistics & numerical data*