when is the first us done in pregnancy
Obstetric ultrasonography 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.[5][10][11] Coincidentally, most miscarriages also happen by 7 weeks' gestation. The rate of miscarriage, especially threatened miscarriage, drops significantly if normal heartbeat is detected.[12]