A simultaneous evaluation of second trimester serum AFP, hCG and unconjugated oestriol as predictors of small for gestational age births

Objectives: To evaluate simultaneously the predictive values of maternal serum alpha-fetoprotein (ms-AFP), human chorionic gonadotrophin (hCG) and unconiugated oestriol(uE3) on the prevalence of fetal growth retardation and small for gestational age (SGA) birth. Method: Midtrimester blood evaluation of ms-AFP, hCG and uE3 was performed in a population of 548 patients who had prenatal care and were delivered at a single institution. Sonographic assessment of fetal growth and evaluation of small for gestational age births was done. Logistic regression analysis with continuous and categorized data was used to evaluate the simultaneous predictive value of midtrimester biochemical markers. Results: In logistic models an abnormal level (≥ 2.5 multiple of median) of ms-AFP was the only independent predictor of SGA (odds ratio = 7.96; 95% confidence interval = 1.04-60.78). When ms-AFP was included in logistic model as a continuous variable, the risk of either SGA or sonographically confirmed intrauterine growth retardation (IUGR) increased by 2.6 and 2.3-fold, respectively, for each multiple of median (MoM) of ms-AFP. Receiver-operator characteristic (ROC) curve study demonstrated that the value of ms-AFP with the simultaneous highest sensibility and specificity in the prediction of SGA, was 1.16 MoM (sensibility = 41.5%, specificity = 80%). An abnormal value of ms-AFP (≥ 2.5 MoM) had a specificity of 99.5% but a sensitivity of 3.5%. Conclusion: Ms-AFP is a better predictor of SGA as compared to both hCG and uE3. Our results suggest that even mild elevations of ms-AFP (> 1 MoM) are a marker of increased risk.