A: In the first few weeks of pregnancy, we typically see a near doubling of the beta hCG levels every 48 hours in healthy intrauterine pregnancies. Of course, there are some exceptions and up to 25 % of normal pregnancies don't have hormone levels that double every 2 days. By 6 weeks, a fetal pole and heartbeat should be seen. Occasionally, if a woman does not have normal menstrual cycles and is not ovulating on day 14 of her cycle, she may not be as far along in her pregnancy as anticipated by the date of her last menstrual period. This is where an ultrasound helps tremendously.
Once a fetal pole and heartbeat are present on ultrasound, hormone levels do not need to be checked and serial ultrasounds can be done instead in order to follow both the growth and heartbeat of the embryo.
Based on the information above, one of two scenarios is possible. Unfortunately, it is possible that your pregnancy may end in a miscarriage if your dates are correct and you are really 7 1/2 weeks based on a normal 28 to 30 day menstrual cycle. It is concerning that your beta hCG levels have not only increased at a lower rate, but also dropped at one point. If, however, your cycles are longer (a 32 or 36 day cycle) you may just be earlier than expected by your dates. Continued ultrasounds and close surveillance by your OB is important to distinguish between the two. And, of course, if you have any vaginal bleeding this should be reported to your OB right away.