title: First trimester aneuploidy screening in the presence of a vanishing twin: implications for maternal serum markers.
abstract: OBJECTIVE
  To assess the impact of a vanishing twin on the levels of the biochemical markers used in the first trimester aneuploidy screening.
  
  
  METHODS
  A retrospective analysis of free beta-hCG and PAPP-A levels in 270 women with a normal singleton fetus with ultrasound evidence of a vanishing twin pregnancy. Marker levels (as MoM) were compared in three groups-76 women with a second empty gestational sac, 194 women with a second gestational sac containing a dead fetus with a measurable crown rump length (CRL), and 1360 matched singleton pregnancies.
  
  
  RESULTS
  In women with a second empty gestational sac, the median free beta-hCG and PAPP-A MoMs (0.968 and 1.040, respectively) were not significantly different from the 1.0 MoM in singleton pregnancies. In the group with a vanished twin with a measurable-CRL-there was a significantly increased median PAPP-A MoM (1.317) but the median free beta-hCG MoM was not changed (1.024). Modelling this bias in PAPP-A MoM the detection rate for trisomy 21 would fall from 85 to 75%.
  
  
  CONCLUSIONS
  First trimester screening in the presence of a vanishing twin may lead to errors in risk estimation. In such circumstances it may be advisable to restrict screening to the use of nuchal translucency (NT) alone.
authors.affiliation: Prenatal Screening Unit, Clinical Biochemistry Department, King George Hospital, Goodmayes, UK. KevinSpencer1@aol.com
authors.forename: K
authors.initials: K
authors.lastname: Spencer
authors.forename: I
authors.initials: I
authors.lastname: Staboulidou
authors.forename: K H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000030:Abortion, Missed / Q000097:blood* / Q000000981:diagnostic imaging; D000328:Adult; D000782:Aneuploidy; D015415:Biomarkers / Q000097:blood*; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D004200:Diseases in Twins / Q000097:blood* / Q000000981:diagnostic imaging; D005260:Female; D005313:Fetal Death / Q000097:blood* / Q000000981:diagnostic imaging; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D012189:Retrospective Studies; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A