title: [Evaluation of plasmatic A protein as only marker during first trimester of pregnancy].
abstract: BACKGROUND
  One of main targets of prenatal diagnosis is Down's syndrome. Biochemical and sonographic markers together are efficient. The use of a single marker has not shown the same efficiency, although it has not been sufficient evaluated.
  
  
  OBJECTIVE
  To shown results of PAPP-A as a single marker in first pregnancy trimester.
  
  
  METHODS
  Prospective, cross-sectional and random study, which evaluated 400 women with biochemical marker PAPP-A in the first pregnancy trimester.
  
  
  RESULTS
  PAPP-A detected a true positive case (0.3%), 28 false positive cases (7.0%) and 371 true negative cases (92.8%), there were no false negative cases. Between 9 to 11 weeks, rate of false positives fluctuated between 5.5 and 6.7%, in 12th week it was 1.2% and in 13th week 18.2%. PAPP-A has 95.1% of specificity (weeks 9 to 12) and 82.2% of maternal age.
  
  
  CONCLUSIONS
  A 5% of false positive rate is acceptable for prenatal diagnosis markers. It has been reported that PAPP-A is less discriminatory at 10 weeks of gestation. In this study the rate fluctuated between 6 and 7% (weeks 9 to 11), which increased at 13th week. Markers with low false positive rate stimulate the use of prenatal screening.
  
  
  CONCLUSIONS
  The use of combined markers: biochemical (free fraction of beta-hGC, PAPP-A) and sonographic, are most recommendable in the first trimester of the pregnancy because of them low rate of false positives. PAPP-A can be used as a single marker between 9 to 11 weeks; false positive cases must be studied with combined markers.
authors.affiliation: Ginecobstetra, Centro Médico del Noroeste. drrsalazar@hotmail.com
authors.forename: Roberto
authors.initials: R
authors.lastname: Salazar López
authors.forename: Ana Lidia
authors.initials: AL
authors.lastname: Ibarra Gallardo
authors.forename: Manuel
authors.initials: M
authors.lastname: Iduma Meléndrez
authors.forename: Rosario
authors.initials: R
authors.lastname: Leyva
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D003430:Cross-Sectional Studies; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis*; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D015415:Biomarkers; D011266:Pregnancy-Associated Plasma Protein-A