Transvaginal scans usually provide clearer pictures during early pregnancy and in obese women.
Also used is Doppler sonography which detects the heartbeat of the fetus.
Doppler sonography can be used to evaluate the pulsations in the fetal heart and bloods vessels for signs of abnormalities.
Traditional obstetric sonograms are done by placing a transducer on the abdomen of the pregnant woman.
One variant, a transvaginal sonography, is done with a probe placed in the woman's vagina.
In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity.
Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.