It can be detected by ultrasound as soon as possible after 35 days of pregnancy. 35 days of pregnancy, which is 35 days from the first day of the last menstrual period, corresponds to 3 weeks after having intercourse during ovulation, a time period just about 2 weeks after the fertilized egg has completed its implantation. A gestational sac of about 0.5 cm in size can be seen by ultrasound, but no germ development or heart tube pulsation can be seen yet. The gestational sac is usually visible on ultrasound at 6-7 weeks after conception and the heart canal is pulsating. In some women, due to irregular menstrual cycles or long menstrual periods, the gestational sac may not be visible until the 6th-7th week of pregnancy, which is also normal.