By the time HCG drops at the beginning of the second trimester, the placenta can make sufficient progesterone to maintain the endometrium. HCG also stimulates the development of fetal gonads and synthesis of androgens by the fetal testes . A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .
Most pregnancy tests depend on the process of agglutination.
Some of the more sensitive tests use monoclonal antibodies rather than sensitized red blood cells. How The Test Will Feel When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing . No special preparation is usually necessary. The test is negative if you are not pregnant .