Objective: To examine the impact of the maternal age-related risk in first-trimester combined screening for trisomy 21.
Methods: Prospective assessment of risk for trisomy 21 by a combination of maternal age, fetal NT thickness and maternal serum PAPP-A and free β-hCG at 11+0 to 13+6 weeks of gestation between April 2002 and February 2007. Screening for trisomy 21 by patient-specific risks based on the maternal and gestational age-related risk multiplied by a likelihood ratio for NT and for maternal serum biochemistry were compared with a screening policy that is only based on the combined likelihood ratio for fetal NT and maternal serum biochemistry.
Results: The study population consisted of 38,603 euploid pregnancies and 109 fetuses with trisomy 21. In screening for trisomy 21 by fetal NT and maternal serum biochemistry in combination with and without maternal age with a fixed false-positive rate of 3%, the detection rate was 82.6 and 79.8%, respectively. In the group of women with a maternal age of less than 30 years and between 30 and 35 years, there was no difference in the detection rate. For women with a maternal age of 35 years or older, the detection rate increased from 77.1% without maternal age to 94.3% with maternal age, respectively.
Conclusion: The overall difference between first-trimester screening based on fetal NT and maternal serum biochemistry with and without maternal age is about 3%. In screening with a fixed cut-off, the maternal age-related risk keeps the false-positive rate low in younger women and increases the detection rate in older women.
2011 S. Karger AG, Basel.