[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.

Materials and 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.

Discussion: 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.