Can blood be used to detect pregnancy?

After 10 days in the same room, women can judge whether they are pregnant by taking blood to detect the concentration of hcg in the blood. The hcg concentration in normal non-pregnant women should be below 5u/L. When the hcg concentration is higher than 10u/L, it can be preliminarily judged that they are pregnant. After 40 days of menopause, B-ultrasound examination can be done to confirm intrauterine pregnancy.