Usually the only symptoms of a chemical pregnancy are a positive pregnancy test and a missed period. According to About.com, many women who have had a chemical pregnancy did not even know they were pregnant.
A chemical pregnancy is basically a very early miscarriage that happens around the 4th or 5th week after a woman's last menstrual period. The miscarriage happens so early that the pregnancy is not detectable on an ultrasound, even though it is detectable with a blood test. According to About.com, once the pregnancy is detectable with an ultrasound, it moves from chemical pregnancy to clinical pregnancy.