How is a twin pregnancy diagnosed?

Michelle Emblenton, biochemist at inviTRA, tells us how to detect a twin pregnancy

Any pregnancy is usually first detected by that positive pregnancy test. The pregnancy test measures the levels of hCG hormone in your blood, the hormone pregnancy. If there are very high levels of this protein present in the very early stages of pregnancy, is the first indication that there may be more than one baby in there. A little bit later in the pregnancy, during an ultrasound or other checkup, in an ultrasound they may see the presence of more than one gestational sac, visualize two little hearts beating or perhaps hear the sound of the two heartblees using the doppler.