At what point during pregnancy are twins discovered?

When I was pregnant with my twin boys, I found out about them at 5 1/2 weeks when we did our first sonogram and saw the heartbeats.

Hi, Miss Management! And congratulations!!!

Typically a woman finds out that she's carrying twins when a doctor does an ultrasound, normally in the first trimester. I found incidences of people finding out as early as 6 or 7 weeks, when their doctor had ordered an ultrasound earlier than normal, perhaps checking gestation date because a woman seems to be growing larger more quickly than expected. In fertility treatments it's common to do an ultrasound early in the trimester to see how many embryos have implanted.

Doctors can hear multiple heartbeats on a Doppler soundwave machine, but it's difficult because there are other sounds that can mask or mimic that second heartbeat.

How far along are you?

Here's a fun quiz that can help you assess your chances of having twins:

http://multiples.about.com/library/signsquiz/bltwinsignsquiz.htm

And here's the top ten signs of a twin pregnancy:

http://multiples.about.com/od/pregnancy/tp/aatpsigns.htm

What runs in your family? Fraternal or identical twins?