Comparison of three first trimester screening algorithms for trisomy 21 with and without adjustment for maternal characteristics.

PURPOSE: Comparison of three algorithms (DoE 2007 and DoE 2011 algorithm of the FMF Germany and MoM algorithm of the FMF UK) in first trimester biochemical screening for trisomy 21 based on maternal and gestational age, free ß-hCG, and PAPP-A and assessment of relevant maternal characteristics.

MATERIALS AND METHODS: Data from 22 449 euploid singleton pregnancies undergoing combined screening for trisomy 21 at 11 to 13 weeks of gestation were examined. The measured maternal free β-hCG and PAPP-A concentrations were converted into DoE 2007 and DoE 2011 values according to the algorithm of the FMF Germany and into MoM values according to the algorithm of the FMF UK. In each pregnancy, patient-specific risks and false-positive rates (FPR) were computed according to the three algorithms and were stratified according to gestational age, maternal ethnicity, maternal weight, and smoking status.

RESULTS: Free ß-hCG and PAPP-A MoM and DoE 2011 were acceptably independent from maternal characteristics and gestational age, while there was a strong relationship between maternal weight and the DoE 2007 values. For a risk cut-off that corresponds to an overall 5 % FPR rate for each algorithm, the FPR in each group were around 5 % at gestational week 11 - 13. The FPR of the DoE 2007 algorithm increased linearly with maternal weight from 3.6 % in women of 50 kg or less to 11.8 % in women of more than 110 kg.

CONCLUSION: Especially maternal weight has a significant impact on the risk calculation. In contrast to the DoE 2007 algorithm, the DoE 2011 and MoM algorithms both adjust for maternal weight.