Hello Thank you for your query. Pregnancy test would be positive on the first day of the missed period itself. THat is, around 4 weeks, as the pregnancy age is calculated from the date of the last menstrual period, and not the date of conception. Hence, by 20th February, you could have been 5 weeks pregnant as per transvaginal ultrasound, because there is a few days error possible in measurement. To know the exact gestational age, you need to specify the date of your last menstrual period, and then corelate it with your next transvaginal ultrasound when the fetus also would be seen ( after 6 weeks pregnancy ) take care, and do not freak out as long as everything is normal