The blastocyst is counted as about 21~23 days of pregnancy after its implantation, but there will be individual differences. For women with regular menstrual cycle, after intercourse during ovulation, fertilization occurs within 24 hours after ovulation, and generally 5~6 days after fertilization, the fertilized egg forms late blastocyst and begins to implant in the uterine cavity and beds in the uterine lining. Therefore, after the blastocyst is implanted, the pregnancy is counted at about 21~23 days, but for women with long menstrual cycles, the week of pregnancy should be estimated by taking into account the actual length of the cycle and the ultrasound examination. Pregnancy can be confirmed by blood HCG (human chorionic gonadotropin) level test about 1 day after the fertilized egg is laid. An ultrasound is also performed at about 6 weeks after menopause to confirm a normal intrauterine pregnancy and to find out about the development of the embryo as well as the fetal buds and heartbeat, and the week of gestation can also be checked based on the size of the fetal buds.