Dr said he couldnt detect a heart beat at 6.4 wks but wasnt sure. ive had light brown discharge and light cramping on and off ?

Difficult: to hear the heart at this time. Don't worry, just continue to take care of yourself. Stay hydrated, eat healthy, avoid alcohol/smoking/drugs, and lightly exercise. He/she will be able to hear a heartbeat in the office at around 10 weeks. Best of luck!

Repeat US and HCG: In one week. Usually fetal heart tones should be seen by week 8, if not, you may be having an early pregnancy loss AKA miscarriage. Do not plan on any air travel until this issues is settled. Long car rides away from hospitals is also ill advised. You may still turn out to have a healthy pregnancy, but one can bleed heavily and even in a life threatening manner during miscarriage. So plan with OB.