title: Monozygotic twinning after assisted reproductive technologies: a case report of asymmetric development and incidence during 19 years in an international group of in vitro fertilization clinics.
abstract: OBJECTIVE
  To describe a case of monozygotic twinning with asymmetric development following a single fresh embryo transfer as part of an intracytoplasmic sperm injection (ICSI) treatment. Secondarily, to report the incidence of monozygotic twinning at the IVI (Instituto Valenciano de Infertilidad) clinics.
  
  
  METHODS
  Case report.
  
  
  METHODS
  Private fertility centers.
  
  
  METHODS
  A 33-year-old woman with a 2-year history of primary infertility.
  
  
  METHODS
  Controlled ovarian hyperstimulation and ICSI treatment with single-embryo transfer.
  
  
  METHODS
  Incidence of monozygotic twinning at the IVI clinics.
  
  
  RESULTS
  We report a twin pregnancy after a single-embryo transfer. Twins were dichorionic and diamniotic. One fetus had a 6-day delay in its growth compared with the other when observed by ultrasound. Two female infants were delivered, and despite presenting congenital diseases, they were successfully treated and evolved correctly. A subsequent DNA analysis confirmed that the infants were monozygotic. Furthermore, we estimated a monozygotic twinning rate of 1.17% at the IVI clinics, taking into account those cases in which two or more embryos with heart beats were observed by ultrasound scanning after single-embryo transfers.
  
  
  CONCLUSIONS
  Ultrasound scans performed during pregnancy suggested a possible dizygotic origin of the twins, but DNA analysis performed after birth established that they were monozygotic. Genetic analysis is the only valid tool to confirm if like-sex dichorionic twins are monozygotic or dizygotic.
authors.affiliation: IVI Sevilla, Sevilla, Spain.
authors.forename: Antonia
authors.initials: A
authors.lastname: Tocino
authors.affiliation: IVI Sevilla, Sevilla, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Blasco
authors.affiliation: IVI Sevilla, Sevilla, Spain; Universidad Pablo de Olavide, Sevilla, Spain.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Prados
authors.affiliation: IVI Sevilla, Sevilla, Spain; Hospital Universitario Nuestra Señora de Valme, Seville, Spain.
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Vargas
authors.affiliation: IVI Madrid, Madrid, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Requena
authors.affiliation: Instituto Valenciano de Infertilidad (IVI), Valencia, Spain; Universidad de Valencia, Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Pellicer
authors.affiliation: IVI Sevilla, Sevilla, Spain. Electronic address: manuel.fernandez@ivi.es.
authors.forename: Manuel
authors.initials: M
authors.lastname: Fernández-Sánchez
mesh_terms: D000328:Adult; D016208:Databases, Factual; D005260:Female; D005298:Fertility; D005820:Genetic Testing; D006801:Humans; D007248:Infertility, Male / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D050498:Live Birth; D008297:Male; D010062:Ovulation Induction; D011237:Predictive Value of Tests; D011247:Pregnancy; D059285:Pregnancy, Twin / Q000235:genetics; D027724:Reproductive Techniques, Assisted; D056826:Single Embryo Transfer; D020554:Sperm Injections, Intracytoplasmic; D016896:Treatment Outcome; D038522:Twinning, Monozygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D016216:Ultrasonography, Prenatal
keywords: Monozygotic twinning; assisted reproductive technologies; asymmetric splitting; single-embryo transfer