Ectopic Pregnancy and Twins

[daniellewngs]

Two totally different topics, but if someone can please explain when you can detect an ectopic pregnancy and twins. I go for my first US tomorrow, I am wondering what news or lack of to expect. If the gestational sac is picked up on the US, would that indicate no ectopic pregnancy. Also, can they detect twins at that time. This is my first pregnancy, all this is very new to me.