Maternal age and amniocentesis: should this be lowered to 30 years?

We have reviewed the results of 10,000 2nd trimester amniocenteses performed at our centre. Over 80 per cent of these were done only because of maternal age (MA); there were three times as many less than 35 year-old women in 1984 compared to 1975. Of women aged 30-34 years at delivery 0.69 per cent were found to have a MA-related chromosome abnormality compared to 0.94 per cent in those aged 35-40 years. Because only about 7 per cent of births occurred to women greater than or equal to 35 years and 18.6 per cent between 30-34 years, and a practical utilization rate of 50 per cent, we recommend that amniocentesis be made available to women aged greater than or equal to 30 years. We believe that 27 per cent of Down syndrome (DS) pregnancies could be identified if 50 per cent of pregnant women in this age category availed themselves of the test. With the same utilization rate, about three times as many amniocenteses would be required in California as performed here in 1983.