Home pregnancy tests detect the pregnancy hormone hCG two to three days before a missed period, according to BabyMed. Although levels fluctuate based on the timing of the implantation of the fertilized egg, the placenta starts manufacturing hCG in detectable levels within 12 and 19 days after ovulation.
The concentration of urine and the quality of the home pregnancy test affect the ability of the test to pick up hCG and render a positive result, notes BabyMed. The sensitivity level of the test also makes a difference in the early detection of the pregnancy hormone. For example, a test with a sensitivity of 20 million international units per milliliter picks up the hormone at half the levels of a test with a sensitivity of 40 million.