Various versions of this blood test exist as double test
or triple test. They are all types of serum screening and
differ only slightly from one another.
The serum screening test is a blood test offered between 15-20 weeks. It combines the results of AFP test with measurement of other chemicals in your blood to give a risk factor for your baby to be born with Down's syndrome.
As the AFP test results are combined with this, the risk factor works out for spina bifida as well.
Depending on your hospital's policy, this test may be offered to all pregnant women or only to older women.