The period between the 5th and 8th week of pregnancy is known as the germ stage. The embryo before the 8th week of pregnancy is known as the germ and can be seen developing by ultrasound between 42-49 days of pregnancy. The germ resembles a small seahorse on ultrasound. With the appearance of the germ, regular heart tube beatings appear. After 8 weeks of gestation the fetus is referred to as a fetus and the pulsations of the heart tube are also referred to as the pulsations of the fetal heart. The fetal germ develops with the number of weeks of gestation. At 4 weeks of gestation, the germ is only 0.2 cm in size and is not visible on ultrasound. At 7 weeks of gestation, the fetal bud grows to 1.33 cm in size, and an ultrasound examination reveals that the embryo has taken on a human form and that the fetal bud and heart tube are beating.