The combination of all four analytes detected 85 percent of trisomy 21 cases at a risk cutoff of one in 270 and one in 190, while the triple screen detected only 69 percent in the study population, at a risk cutoff of one in 190. A more recent prospective study 17 of women with an average age of 35.9 years demonstrated that the addition of inhibin A to the triple screen was actually the best combination of analytes. An initial retrospective study 19 suggested that AFP, hCG and inhibin A analytes might be a better combination than AFP, hCG and unconjugated estriol. Inhibin A, a glycoprotein synthesized by the gonads, corpus luteum, decidua and placenta, is the latest maternal serum analyte to show promise as a screening agent in clinical studies. Counseling patients about the risks and benefits of such screening is important to provide a balanced discussion of screening issues. Adding hCG and unconjugated estriol to this screen increases the rate of detection of trisomies 21 and 18.

Measurement of AFP alone can detect the vast majority of neural tube defects and a small portion of trisomy 21–affected pregnancies in patients of all ages. The current maternal serum analytes in use in most areas are alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG) and unconjugated estriol. The issues facing physicians are the sensitivity and specificity of multiple serum analyte combinations. There have been some changes in the recommended method of prenatal screening over the past few years, and research to improve detection rates with better combinations of maternal serum analytes is ongoing. According to the American College of Obstetricians and Gynecologists, it has become standard in prenatal care to offer screening tests for neural tube defects and genetic abnormalities.

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