Various pregnancy tests are available.They are:
1.Human chorionic gonadotropin(hCG) is the earliest test for pregnancy that can help the diagnosis of pregnancy.The level of hCG increases until it peaks at about 60 days of gestation and then declines until about 140 days of pregnancy.The production of human chorionic gonadotropin(hCG) begins as early as the day the embryo is implanted in the uterus and hence it can be detected by a simple blood test.First voided urine also will have hCG.So this can be confirmed by a home pregnancy kit.
2.Immunoassay or agglutination inhibition tests(AITs) depend on antigen-antibody reaction between hCG and an antiserum.The antiserum is mixed with urine and hCG coated particles.If hCG is present in the urine,agglutination doesnot occur.This test can be performed after 6 weeks of gestation.
3.Radioimmunoassay(RIA) tests identifies the beta subunit of hCG in the blood and urine.Radioactive labeled markers are used for this test.This test can be done right after a week of gestation.
4.Radioreceptor assay (RRA) is a blood test that helps to determine the ability of the blood to inhibit the binding of radiolabeled hCG to receptors.This test can also be done after a week of conception.
5.ELISA or enzyme-linked immunosorbent assay uses a specific monoclonal antibody with enzymes to bond with hCG in the urine.This is the most commonly used test available.It can be done at home.This is the principle employed in the home pregnancy tests.Pregnancy as early as 4 days can de confirmed with this test.This test indicates a colour change.Instructions in the kit are helpful to proceed with this test.It can be simply bought from a pharmacy.