First trimester biochemistry at different maternal ages.

Background: The performance of first trimester biochemical screening was compared at different pregnancy weeks and maternal ages during 2002-2008 in a screened population of 76,949 women.

Methods: The detection rates, as well as the median multiples of a median (MOMs) of free β-human chorionic gonadotropin (free β-hCG) and pregnancy-associated plasma protein-A (PAPP-A), were compared between completed gestational weeks 8-13 and between different maternal ages separated into 5-year groupings.

Results: The number of singleton Down syndrome pregnancies was 221. The median age of the screened women was 30 years and the proportion of women aged ≥ 35 years 16.9%. The median age of the women with a Down syndrome pregnancy was 37 years. In women aged <35 years, the biochemical markers provided a detection rate of only 38.6%, whereas in women aged ≥ 35 years, the biochemical markers detected 82.7% of cases (p<0.01).

Conclusions: Biochemical screening works best amongst women aged ≥ 35 years. For younger mothers aged <35 years, combined screening should be the method of choice.