After fertilization the embryo implants in the endometrium and begins secreting a hormone called chorionic gonadotropin (CG), after implantation. CG functions to prevent the corpus luteum from degenerating so that it may continue to produce estrogen. Without visiting doctor and without invasive methods pregnancy can be determined by
Develop a test to detect CG in the mother's urine
This hormone comes in the urine after the concentration of this hormone increases in blood which can be determine after 10 days from missing the date of the last month period because this hormone doubles every 2 to 3 days during the first several weeks of pregnancy. This is a noninvasive method and can be done at home by doing urine test by using pregnancy kit test.
Among the other 3 remaining options blood test is invasive method and the rest of the 2 options needs visit to a doctor.