Fine-tuning of routine combined first- trimester screening: The ratio of serum-free- beta-human chorionic gonadotropin (fβ-hCG) to pregnancy-associated plasma protein-A (PAPP-A) could improve performance of Down syndrome screening program, a retrospective cohort study in Iran

OBJECTIVES: To evaluate the performance of the current national screening policy for Down syndrome (DS) in Iran and suggest a more efficient protocol with a wealth of a large series of first-trimester screening (FTS) data obtained from Nilou medical laboratory. To fulfill this aim, detection rate (DR), positive screening rate (PSR), false negative rate (FNR) and odds of being affected given a positive results (OAPR) were calculated at different cutoff risk. In the latest update of DS screening program in Iran, there is no place for intermediate group to be further investigated. Next, we proposed a novel parameter namely the ratio of fβ-hCG multiple of the median (MoM) value to PAPP-A MoM value to delicately categorize FTS results in a way that reduce FNR without imposing unnecessary anxious and extra money on most families. METHODS: The present investigation was conducted retrospectively on 197,210 pregnancies undergoing FTS for aneuploidies in Nilou medical laboratory, Tehran, Iran, from March 2015 to February 2016. RESULTS: Intermediate risk group is important as 23 out of 45 FN fell in the range 1:250 to 1:1100. By applying the proposed index, the ratio of fβ-hCG MoM to PAPP-A MoM and subsequent decision about NIPT, 8 out of 23 FN cases in intermediate group could be detected. CONCLUSION: Compared with the current policy, our novel proposed approach had better performance and could be applied by the Iran National Health Service to improve the screening program guideline.