Efficacy of a Two-Marker Test Followed by Ultrasound for Antenatal Screening of Trisomy 18

Abstract

To evaluate the efficacy of two-marker serum testing followed by ultrasound for antenatal screening for trisomy 18. Alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG) data from the maternal serum screening program at Taiwan Adventist Hospital were collected for gestations between 15 and 21 weeks. We calculated the screening positivity rate and sensitivity at various cutoff values. The results of fetal ultrasound were also collected. With the cutoff values of maternal serum AFP ≤0.75 multiples of the median (MoM) and hCG ≤0.55 MoM, two-marker testing yielded a sensitivity of 88.9%, with a screening positivity rate of 3.5%. Using cutoff values of AFP ≤0.6 MoM and hCG ≤0.5 MoM, a much lower screening positivity rate with similar sensitivity was found. Subsequent comprehensive ultrasound examination may markedly reduce the need of amniocentesis. We do not suggest offering routine amniocentesis to pregnant women based on the results of two-marker testing for trisomy 18. Women with positive serum test results should be carefully monitored with level II ultrasonography. Amniocentesis is recommended only in cases of a positive serum screening result and an abnormal fetal ultrasound.