title: Factors associated with monozygosity in assisted reproductive technology pregnancies and the risk of recurrence using linked cycles.
abstract: OBJECTIVE
  To evaluate factors associated with monozygosity (MZ) (number of fetal heartbeats on early ultrasound greater than the number of embryos transferred) and the risk of recurrence in subsequent pregnancies using a national assisted reproduction database.
  
  
  METHODS
  Historical cohort study.
  
  
  METHODS
  Clinic-based data.
  
  
  METHODS
  197,327 pregnancies (including 2,824 with evidence of MZ) from cycles reported to the Society for Assisted Reproductive Technology Clinic Outcome Reporting System (SART CORS) between 2004 and 2010.
  
  
  METHODS
  None.
  
  
  METHODS
  Evidence of MZ, adjusted odds ratios and their 95% confidence intervals computed from logistic regression models.
  
  
  RESULTS
  In the univariate analysis, the risk of MZ was increased with ovulation disorders, donor oocytes, gonadotropin-releasing hormone agonist (GnRH-a) suppression, assisted hatching (AZH), and day 5-6 transfer, and was decreased with higher follicle-stimulating hormone (FSH) doses (≥3,000 IU). In the multivariate analysis, the risk of MZ was increased with GnRH-a suppression, AZH, and decreased with intracytoplasmic sperm injection (ICSI) and higher FSH dose. The interaction showed that although MZ was more likely with day 5-6 embryos, AZH had a minimal nonsignificant effect, whereas in day 2-3 embryos, AZH had a substantial statistically significant effect. Only one woman had a recurrence of MZ in a subsequent assisted reproduction pregnancy, which is consistent with randomness.
  
  
  CONCLUSIONS
  The risk of MZ was higher with fresh day 5-6 embryos, donor oocytes, GnRH-a suppression, lower FSH doses, and AZH (particularly with day 2-3 embryos).
authors.affiliation: Department of Obstetrics, Gynecology, and Reproductive Biology, Michigan State University, East Lansing, Michigan. Electronic address: lukeb@msu.edu.
authors.forename: Barbara
authors.initials: B
authors.lastname: Luke
authors.affiliation: Department of Biostatistics, School of Public Health, University of Michigan, Ann Arbor, Michigan.
authors.forename: Morton B
authors.initials: MB
authors.lastname: Brown
authors.affiliation: Redshift Technologies, New York, New York.
authors.forename: Ethan
authors.initials: E
authors.lastname: Wantman
authors.affiliation: Department of Obstetrics and Gynecology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire.
authors.forename: Judy E
authors.initials: JE
authors.lastname: Stern
mesh_terms: D000328:Adult; D015331:Cohort Studies; D004624:Embryo Transfer / Q000009:adverse effects* / Q000379:methods*; D005260:Female; D006801:Humans; D008597:Menstrual Cycle / Q000502:physiology*; D008875:Middle Aged; D018587:Oocyte Donation / Q000009:adverse effects / Q000379:methods; D011247:Pregnancy; D012008:Recurrence; D027724:Reproductive Techniques, Assisted / Q000009:adverse effects*; D012307:Risk Factors; D013997:Time Factors; D014430:Twins, Monozygotic / Q000235:genetics
keywords: Assisted hatching; GnRH-a suppression; blastocyst transfer; monozygosity