no heartbeat at early 6 week fine? can I expect it in 8 week ultrasound? which week should I do anomaly test for defect identification,if any

A. A fetal heartbeat may first be detected by a vaginal ultrasound as early as 5 1/2 to 6 weeks after gestation. That's when a fetal pole, the first visible sign of a developing embryo, can sometimes be seen. But between 6 1/2 to 7 weeks after gestation, a heartbeat can be better assessed