<Li> <P> Fetus at 20 weeks </P> </Li> <P> Fetus at 20 weeks </P> <P> A gestational sac can be reliably seen on transvaginal ultrasound by 5 weeks' gestational age (approximately 3 weeks after ovulation). The embryo should be seen by the time the gestational sac measures 20 mm, about five - and - a-half weeks . The heartbeat is usually seen on transvaginal ultrasound by the time the embryo measures 5 mm, but may not be visible until the embryo reaches 7 mm, around 7 weeks' gestational age . Coincidentally, most miscarriages also happen by 7 weeks' gestation . The rate of miscarriage, especially threatened miscarriage, drops significantly if normal heartbeat is detected . </P> <Ul> <Li> <P> Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age . </P> </Li> <Li> <P> Artificially colored, showing gestational sac, yolk sac and embryo (measuring 3 mm as the distance between the + signs). </P> </Li> <Li> <P> Embryo at 5 weeks and 1 day of gestational age (at top left) with discernible heartbeat . </P> </Li> <Li> <P> Embryo at 5 weeks and 5 days of gestational age with discernible heartbeat . </P> </Li> </Ul>

When is the first us done in pregnancy