[Specificity of biochemical markers of pregnancy second trimester]

Abstract

Background: During the second trimester of 21 trisomy pregnancies, median of maternal serum concentrations of alpha-fetoprotein, not conjugated estriol, beta fraction, and inhibin A differ from normal values, and it can be used to select high risk patients.

Objective: To evaluate specificity of different forms of second trimester biochemical markers association in a group of healthy pregnant women and determine levels considered as low risk.

Patients and methods: Random and cross-sectional study in 363 pregnant women with prenatal diagnosis to evaluate specificity of different combinations of biochemical markers. Down's syndrome and defects of neural tube rates of detection were defined as the percentage of pregnancies with tests of detection of true negatives and false positives.

Results: Total beta fraction has differences during weeks 13 to 14, with 70% of cases between 23,000 to 70,000 units, with 1.38% of false positives; alpha-fetoprotein fluctuated between 22 to 30 units, with 5.2% of false positives; conjugated estriol increases between 1.2 to 2.2 units during 2nd quarterly, with 6.3% of false positives; and inhibin has an increase, with 70% of cases located between 125 to 486.5 units, with 10.44% of false positives.

Conclusions: Marker formula with greater specificity was type IV, included alpha-fetoprotein, not conjugated estriol and beta fraction. In the isolated form, alpha-fetoprotein marker demonstrates greater specificity.