title: Monozygotic twinning: an eight-year experience at a large IVF center.
abstract: OBJECTIVE
  To characterize incidence, chorionicity, amnionicity, and pregnancy outcome for monozygotic twin pregnancy (MZT) after IVF.
  
  
  METHODS
  Retrospective review.
  
  
  METHODS
  University-based fertility center.
  
  
  METHODS
  Autologous and oocyte donation IVF cycles eventuating in 4,976 clinical gestations from 2000 to 2007.
  
  
  METHODS
  None.
  
  
  METHODS
  MZT incidence, chorionicity, zygosity, pregnancy outcome.
  
  
  RESULTS
  Ninety-eight MZTs were diagnosed after first-trimester ultrasound evaluation (2% incidence). The incidence in cycles transfering autologous oocytes was 1.7% but was 3.3% with donor oocytes; however, women <35 years old using their own oocytes displayed a similar rate (3.1%) to women using donor oocytes. Eighty MZTs occurred after fresh day-5 transfer; only 14 followed fresh day-3 transfer (2.6% vs. 1.2%). The MZT incidence in day-3 transfers without hatching was not different from those with hatching (1.3% vs. 1.1%). In addition, MZT incidence did not differ significantly whether or not ICSI was performed (2.4% vs. 2.0%). Four MZTs occurred after frozen-thawed embryo transfer (0.8% incidence). Ninety-five percent of all placental arrangements were confirmed as monochorionic-diamniotic on obstetric ultrasounds.
  
  
  CONCLUSIONS
  These findings confirm a higher incidence of MZT after IVF. Monochorionic-diamniotic implantations were increased, whereas monochorionic-monoamniotic were not. The MZT risk factors included young age and extended culture, but not zona penetration or cryopreservation.
authors.affiliation: New York University Fertility Center, New York University-Langone Medical Center, New York, NY 10021, USA.
authors.forename: Jaime
authors.initials: J
authors.lastname: Knopman
authors.forename: Lewis C
authors.initials: LC
authors.lastname: Krey
authors.forename: Jennifer
authors.initials: J
authors.lastname: Lee
authors.forename: Mary Elizabeth
authors.initials: ME
authors.lastname: Fino
authors.forename: Akiva P
authors.initials: AP
authors.lastname: Novetsky
authors.forename: Nicole
authors.initials: N
authors.lastname: Noyes
mesh_terms: D000650:Amnion / Q000166:cytology; D001755:Blastocyst / Q000166:cytology; D002823:Chorion / Q000166:cytology; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D008297:Male; D018587:Oocyte Donation / Q000706:statistics & numerical data; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D038522:Twinning, Monozygotic; D016216:Ultrasonography, Prenatal