This is a protocol for a Cochrane Review (Diagnostic test accuracy). The objectives are as follows:

To compare different screening methods in isolation, and in various combinations to identify the most sensitive and specific test or tests for Down’s syndrome in the antenatal period.

Screening tests will be compared with respect to the following:

• proportion of screened fetuses with Down’s syndrome detected by screening before birth;

• the number of women with a high risk screening test result who subsequently have an unaffected pregnancy;

• the number of invasive diagnostic procedures in women with fetuses subsequently found to have a normal karyotype;

• the number of iatrogenic miscarriages in women with fetuses subsequently found to have a normal karyotype; and

• the number of other adverse effects of screening and diagnosis.