First-trimester aneuploidy screening: is there a maternal age at which it loses effectiveness?

To determine the maternal age at which the likelihood of a "screen-positive" result justifies diagnostic testing.

A retrospective review of women who presented for first-trimester screening using nuchal translucency (NT) measurements with or without serum biochemistry between January 2000-December 2011. Using cutoffs of 1:300, 1:270, and 1:200, the Trisomy 21 (T21) screen-positive rates were stratified by maternal age.

A total of 6,927 women underwent first-trimester screening; women with multiple gestations and/or using donor oocytes were excluded. Of the remaining women, 4,882 had combined NT and biochemistry results, while 1,767 had NT without serum screening results. Screen-positive rates were stratified by maternal age. An increase in the screen-positive rate is noted for both groups after age 40 but is more pronounced after age 43, where the screen-positive rate is 97.8% and 63.0% using cutoffs of 1:300 for the NT and NT and Biochemistry groups, respectively.

Women undergoing first-trimester screening at age 40 have approximately 30% likelihood of screening positive for T21. This rate increases to roughly 70-90% at age 44. This information will affect the counseling of patients who are considering prenatal screening versus diagnosis.