Temporal trends of prevalence of and critical titer of high-risk alloantibodies at initial prenatal visit from 2010 to 2021. (A) The temporal increase in positive detection of the 3 alloantibodies (anti-D, anti-c and anti-Kell) considered high-risk for alloantibodies over a 12-year period. This temporal trend was significant for all 3 alloantibodies (all P < .001) and most notable for anti-D, for which the prevalence rose 43.0% from 481 per 100 000 pregnancies in 2011 to 688 per 100 000 in 2021. (B) The frequency of critical titers for all 3 high-risk abs. These frequencies changed over the 12-year period (P < .001 for both anti-K and anti-D; P = .03 for anti-c). The prevalence of critical titer of anti-K increased 25.6% from 39 per 100 000 in 2011 to 49 per 100 000 in 2021, whereas that of anti-D decreased 21.7% from 23 per 100 000 in 2010 to 18 per 100 000 in 2021.