Pregnancy tests are done to detect the hormone human chorionic gonadotropin hormone (HCG) in urine and blood which will be present only in a pregnant woman. It can be checked at home also and are similar to the test done in health care offices.

Pregnancy can also be detected by ultrasound scan. The gestational sac can be visualized as early as four and half weeks of gestation approximately about two and half weeks after ovulation. Yolk sac can be detected at about five weeks of gestation. The embryo can be seen by 7 weeks of gestation.

During pregnancy, the egg is fertilized by the sperm in the fallopian tubes. Within 9 days after fertilization the fertilized egg moves down the fallopian tube in to the uterus and gets attached (implants) to the wall of uterus. During this time, the placenta starts developing and releases HCG hormones in to the blood. Some of these hormones are also passed in urine. The amount of HCG in the urine higher and doubles every 2 to 3 days.

The test for pregnancy which will give the quick result after fertilization is the rosette inhibition assay for early pregnancy factor. This can be detected in the blood within 48 hours of fertilization, but this method is expensive and time-consuming.

Most pregnancy tests look for the presence of beta subunit of HCG hormone in the blood or in the urine. It is detected in urine of blood after implantation which is about 6 to 12 days after fertilization.

Blood tests or serum tests can detect HCG levels as low as 1 mIU/mL. Urine test can detect if the HCG level from 20 to 100 mIU/mL.

When to do pregnancy tests:

• Blood tests are more sensitive and detect the HCK immediately after implantation, which is about six to twelve days after ovulation. Urine tests will detect HCG after three to four days after implantation.
• Urine pregnancy tests are usually done in a woman after 7-10 days after missing the periods.
• A false positive result is that the tests shows positive result, but the woman is not pregnant. It can occur due to error in the test, use of drugs which contain the HCG, in woman who has taken HCG injection for infertility.  Some diseases of the liver, cancers produces increased HCG levels which include choriocarcinoma, germ cell tumors etc. Drugs like diuretics can also cause false positive results.
• A false negative pregnancy test which means that the woman is pregnant but the test is negative is seen if the tests are done too early.

How to do home pregnancy test:

• Perform the test in the early morning and use mid stream urine that is passing the urine a bit and then collect the urine for the test.
• Pregnancy test kits are stored in the refrigerator. Bring the test kit to room temperature before you use it.
• Collect urine in a clean, dry glass or plastic container. See to that there is no soap residue in the container.
• Draw little urine with a dropper provided with the kit and put 2 drops in the test well. Do not spill the urine on reading stip.
• Wait for about 3 to 5 minutes and then read the result.

Interpretation of results:

• See the regions marked ‘C’ and ‘T’ over the kit. ‘C’ indicates control and ‘T’ indicates test sample.
• If only one pink or purple band appear in the region ‘C’, indicates that the pregnancy test is negative.
• If two pink or purple bands occur, one in the ‘C’ region and another in the ‘T’ region, indicates that the test is positive.
• If the line formed on the ‘T’ region is faint, indicates low levels of HCG. In this case repeat the test after 72 hours using new kit.
• If there are no bands, indicates that the test is invalid. Repeat the test with new kit after 72hours.