Aim: To study pregnancy diagnosis test.
Requirements: Anyone marketed single-use pregnancy detection kit (which contains 1 test device and 1 disposable dropper, vial), urine sample.
Principle: A pregnancy test helps to determine whether a woman is pregnant or not. The fertilized egg secretes the hormone called Human Chorionic Gonadotropin (HCG) which is found in urine during early pregnancy. When urine sample of pregnant women is reacted with specific HCG antibodies; precipitation, haemagglutination or complement fixation like reaction occurs which is used as a diagnostic test for pregnancy.
These tests can be performed using immunological, biological and radiological techniques.
I. Immunological tests: These are commonly used and performed with the help of readily available marketed kits based on the reaction between urine HCG and specific HCG antibodies.
Working Principle of Immunological Test: This test gives qualitative detection of HCG in the urine. It is based on the combination of urine HCG with monoclonal antibody–dye conjugate and polyclonal HCG antibodies present on the strip of a diagnostic kit. A urine sample is applied to the test zone of the strip. If HCG is present, an antibody-HCG-antibody dye complex will be formed and a pink-purple coloured band develops. A control zone is provided to check the potency of the test reagents, flow and volume of urine added.
II. Biological tests involve the injection of urine samples into various animals. They are accurate but time-consuming and costly.
III. Radiological tests are performed by Radioimmunoassay (RIA) and Enzyme-linked immune sorbent assay (ELISA) techniques using radio-labelled HCG and its specific antibodies.
IV. Ultrasonography is a reliable method for detecting pregnancy that uses pulses of ultrasonic waves at high frequency on various parts of the uterus. The echoes (reflected waves) are displayed on the ultrasound screen and thereby confirm pregnancy. The pregnancy can be evident as early as the 5th week.
Procedures:
- Collect the first urine sample in the morning in a clean container (The first few ml of urine shall be discarded and then collected).
- Add 2-3 drops of urine on the strip and observe the colour change of the bands, if any, on the test and control zones.
- Read the results as positive (i.e. development of pink or purple colour on both control and test zone) or negative (i.e. development of pink or purple colour only on control zone).
Note: False positive (test is positive but the female is not pregnant) or false negative (test is negative but the female is pregnant) result is the major limitation of this test.
| Sr. No. | Test result | Major reasons |
| 1. | False-positive | • Excess protein • Blood in urine • HCG production due to cancerous condition • Diuretics |
| 2. | False-negative | • Too early testing • Ectopic pregnancy • Benzodiazepines |
Observation Table:
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