At 2 months of pregnancy, no heart tube is normal?

Patient's question:

The last menstrual period came on November 20th, about 5 days later than October
I had brown discharge on December 22nd, and on December 29th, I took a pregnancy test and had an ultrasound, which only showed a gestational sac
Sometimes I have abdominal pain, especially when sitting for a long time, but it's better when lying down

Doctor's answer:

Under normal circumstances, fetal heartbeat can be observed on vaginal ultrasound or abdominal ultrasound at 5-6 weeks of pregnancy. After 7-8 weeks of pregnancy, the ultrasound can clearly show the fetal heartbeat. At this time, the heart rate and rhythm can be measured using M-mode ultrasound, with the heart size being approximately 2mm. If the ultrasound image clearly shows an embryo without a heartbeat, it often indicates embryonic death and inevitable miscarriage. However, if the ultrasound examination is performed too early, the absence of a germinal disc and heartbeat cannot be considered abnormal.