Failed implatations do not cause any symptoms and occur for a multitude of reasons where conditions for the pregnancy to continue are just not right. This is not classed as a true miscarriage but as a failed implantation. There are many reasons that this may occur and it may be natures way of ensuring that only the best embryos continue. Ultra pregnancy tests
will detect some of these implantations and for this reason it is important to confirm the continued implantation and development of the pregnancy with a repeat pregnancy test a week to 10 days after the initial positive result. You would expect to get a stonger line on the pregnancy test at this point if you are tesing at the same time of day as the hormone levels should have increased.