From the internet.............Hope it is helpful.........The term chemical pregnancy means that the miscarriage happened at a point that a missed period and biochemical tests, such as an hCG blood test or a home pregnancy test (checking hCG in urine), were the only evidence that you were pregnant. The miscarriage happened before an ultrasound could have shown a gestational sac.
When the pregnancy develops to the point that ultrasound could confirm the existence of the pregnancy, the term becomes clinical pregnancy. Thus, a chemical pregnancy would be a miscarriage before the fifth week of gestation -- or within about week after your missed menstrual period.
at 2:55 PM on Oct. 13, 2010