At which month can a ultra sound show twins?

The best and most reliable way to confirm a twin or multiple pregnancy is to see it with an ultrasound. An ultrasound is the only guaranteed way to know whether you're carring more than one baby. An ultrasound may be able to detect multiple embryos as early as your third week of pregnancy; However, the ultrasound will be most reliable at detecting a multiple or twin pregnancy at around 6 to 8 weeks.