title: The incidence of monozygotic twinning following PGD is not increased.
abstract: BACKGROUND
  Monozygotic (MZ) twin pregnancies are associated with increased perinatal mortality and morbidity, and risk of congenital anomalies. The causes of MZ twinning in humans are unclear but the incidence may increase after PGD, for example, as a result of holes created in the zona pellucida. We compared the incidence of MZ twin pregnancies in ICSI cycles with PGD, versus ICSI cycles without PGD.
  
  
  METHODS
  In this retrospective comparative cohort study, we analysed incidence of twin pregnancies in unselected patients undergoing ICSI and PGD (group A; 1992 cycles) with blastocyst transfer at Day 5, versus a period-matched control population of unselected patients undergoing ICSI and blastocyst transfer at Day 5 without PGD (group B; 2429 cycles) from January 2001 to December 2006.
  
  
  RESULTS
  Clinical pregnancy per embryo transfer was established in 618/1992 (31.0%) and 947/2429 (39.0%) in group A versus B, respectively (P < 0.01). Overall MZ twin rate was 29/4421 (0.7%) per embryo transfer and 29/1565 (1.9%) per established clinical pregnancy. The incidence of MZ twinning per established clinical pregnancy did not differ between groups (1.5 versus 2.1%, group A and B, respectively). In group A, seven MZ twins were born versus 19 MZ twins in group B. In group B, one MZ twin pregnancy resulted in two stillbirths. In group A, two MZ twins had severe congenital malformations versus none in group B.
  
  
  CONCLUSIONS
  The incidence of MZ twinning was not increased in PGD compared with regular ICSI with blastocyst transfer. This information is useful in counselling patients about potential risks of PGD.
authors: Centre for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, 101 Laarbeeklaan, B-1090 Brussel, Belgium. willem.verpoest@uzbrussel.be
authors: W
authors: W
authors: Verpoest
authors: L
authors: L
authors: Van Landuyt
authors: S
authors: S
authors: Desmyttere
authors: A
authors: A
authors: Cremers
authors: P
authors: P
authors: Devroey
authors: I
authors: I
authors: Liebaers
mesh_terms: D000328:Adult; D015331:Cohort Studies; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D015994:Incidence; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D011272:Pregnancy, Multiple; D019836:Preimplantation Diagnosis / Q000009:adverse effects*; D012189:Retrospective Studies; D018570:Risk Assessment; D020554:Sperm Injections, Intracytoplasmic; D038522:Twinning, Monozygotic