Trends in the use of prenatal diagnosis in New York State and the impact of biochemical screening on the detection of Down syndrome: 1984-1993.

Our purpose was to examine trends over time in the use of prenatal cytogenetic diagnosis by New York State women from 1984 to 1993 in the context of new technologies in prenatal diagnosis and pregnancy management. Data are from the New York State Chromosome Registry and represent 95-98 per cent of all New York State women tested. Utilization rates were calculated separately for women under 35 years of age and for those aged 35 years and over. Analysis of longitudinal trends also utilized data from 1979 to 1983. Utilization by women under age 35 increased steadily over time but levelled off after 1986 among older women. Each year, there was an increase in the proportion of tests performed during the first trimester. The proportion of first-trimester tests performed with chorionic villus sampling (CVS) decreased from a maximum of 68 per cent in 1987 to 10 per cent in 1993. The percentage of tests performed due to 'advanced maternal age' decreased over time while 'suspected fetal pathology' categories increased in frequency. The increase in prenatal diagnosis tests performed because of abnormal maternal serum markers was associated with an increase over time in the number and proportion of Down syndrome fetuses detected prenatally and a slight decrease in the prevalence of Down syndrome among live births. The trends reported here parallel improvements in biochemical screening for Down syndrome and published suggestions that all women aged 30 and over are offered prenatal diagnosis.