In Reply: Data from Dr Resta's article1 indicate that he is correct in stating that the increasing number of pregnancies occurring in women who are 35 years of age and older has recently resulted in that cohort accounting for slightly more than half the number of Down syndrome fetuses conceived in the United States. As the proportion of older women in any pregnancy cohort increases, there will be a concomitant redistribution of Down syndrome cases in that population. In the FASTER trial,2 where 21.6% of the screened population was aged 35 or older, compared with 14% for the US population, 69% of the Down syndrome cases occurred among those older women.
Berkowitz RL, Roberts J, Minkoff H. Maternal Age–Based Prenatal Genetic Testing—Reply. JAMA. 2006;296(8):930. doi:10.1001/jama.296.8.930-b