There are many tests available with which pregnancy can be detected as early as possible. The basis of detection of pregnancy is the production of hormone called beta human chorionic gonadotrophic hormone (Beta HCG). The production of this hormone starts approximately 6 days after the process of fertilization.
According to the female reproductive system functioning, ideally fertilization takes place on 14th day of menstrual cycle. Presuming that fertilization has also occurred on the same day, we have various tests that can detect pregnancy as early as 7 days after fertilization.
Immuno Radio Metric Assay (IMRA) is one such test, with which the pregnancy can be detected as early as 7 days (7 days before the missed period) after fertilization. It is the most sensitive test available for early detection of pregnancy. The only limitation of this test is that it is very expensive.
Enzyme Linked Immuno Sorbant Assay (ELISA) is the second best test employed to detect the pregnancy. It can detect the pregnancy after 9 days of fertilization (5 days before the missed period). It is also highly sensitive in detecting the pregnancy.
Radio Immune Assay (RIA) is one of the most sensitive and also most specific test that is employed for detection of pregnancy. It can detect pregnancy within10 days after fertilization (4 days before missed period). It is the investigation of choice used in the recent times for quantitative assessment of pregnancy.
Urine Pregnancy Test (UPT) is one of the most popular tests employed for the detection of pregnancy. It is one of the qualitative methods of detection of pregnancy and it requires the presence of the hormone beta HCG in urine. It detects the pregnancy immediately after the missed period (14 days after fertilization). There are various kits available in the market, with which the pregnancy can be detected at home, without requiring any hospital referral.
The pregnancy can be detected within one week of fertilization presuming that the menstrual cycles are normal and occur once in every 28 days.