Variation in biochemical screening for Down's syndrome in the United Kingdom.

A questionnaire survey was undertaken of all 73 laboratories performing Down's syndrome screening in 1995. An estimated 352,000 tests were performed representing 47% of maternities. Three-quarters of these tests have ultrasound dating information at the time of testing. The majority of laboratories (70%) commenced screening at 15 weeks of gestation or later, and there was considerable variation in the upper limit of screening (17 to 24 weeks). Eighty-six percent of laboratories screened all women regardless of age. The reported Down's syndrome risk was based on term in 85% of laboratories. There was an inconsistent approach to determining and reporting high risk for trisomy 18 (Edwards' syndrome): 5% reported risks on report forms and 42% notified the clinicians if the risk was considered to be raised.