Pregnancy can typically be detected by ultrasound from about five and a half to six weeks after the last menstrual period. At this early stage, an ultrasound can show a gestational sac in the uterus, and by around six weeks, a fetal pole or embryo may be visible. The detection is usually done using a transvaginal ultrasound, which provides clearer images in early pregnancy. The embryo with a heartbeat can generally be seen between 12 to 17 days after a missed period, which corresponds roughly to six weeks gestation. Ultrasounds before this time may not reliably show a pregnancy. Early ultrasounds are also important to confirm whether the pregnancy is viable and properly located inside the uterus, especially to rule out ectopic pregnancy. Low-risk pregnancies often have their first ultrasound later, around eight weeks or more. While pregnancy tests can detect pregnancy slightly earlier, ultrasound visualization usually happens about a week after the earliest positive pregnancy test.
