Insulin-like Growth Factor Binding Protein-3 in the Detection of Fetal Down Syndrome Pregnancies

Objective: To study the usefulness of maternal serum insulin-like growth factor binding protein-3, a potential cell growth inhibitor, in second trimester prenatal screening for fetal Down syndrome. Methods: Three hundred and forty-two samples from normal pregnancies and nine fetal Down syndrome pregnancies were analyzed for insulin-like growth factor binding protein-3 levels by radioimmunoassay. Data were converted to multiples of median (MoM) and analyzed statistically to compare the differences between control and Down syndrome pregnancies. Results: The mean insulin-like growth factor binding protein-3 MoM of Down syndrome–affected pregnancies (1.09) was significantly higher than that of the normal pregnancies (1.00) ( P < .01). Insulin-like growth factor binding protein-3, in combination with maternal serum alpha-fetoprotein (MSAFP), hCG, and maternal age, detected 89% of Down syndrome pregnancies at a screen positive rate of 2.1%. This compares favorably to the standard combination of MSAFP, hCG, and unconjugated estriol (E3), which had a 66.7% Down syndrome detection rate and a 4.1% screen positive rate in our study samples. Conclusion: This retrospective analysis suggested that the inclusion of insulin-like growth factor binding protein-3 into the triple screen program to replace unconjugated E3 might enhance the detection rate of fetal Down syndrome pregnancies. These data need to be confirmed by a larger prospective study.