There are several reasons why you might not see the fetus’s heartbeat at eight weeks. First, you may not really be eight weeks pregnant. You may have menstrual cycles longer than 28 days, or you may have ovulated late that cycle.
The second reason has to do with the type of ultrasound probe your doctor is using.Transabdominal probes (over the belly as opposed to in the vagina) are not as sensitive in detecting pregnancy and early heartbeat.
A heartbeat definitely should be seen if an embryo (or “fetal pole”) is seen, usually as early as six weeks of pregnancy by transvaginal ultrasound.