24 weeks pregnant (twins), originally uploaded by rms519.

Here are some of the most common signs of a twin or multiple pregnancy.
1. History/Hunches
A family history of multiples, or a powerful hunch can be convincing indicators.
2. Weight Gain
Just as a multiple pregnancy may cause a mother to measure large, it may also result in an increased weight gain.
3. Doppler Heartbeat Count
Using harmless sound waves, a Doppler system amplifies fetal heart sounds, usually distinguishable late in the first trimester.
4. Ultrasound Confirmation
The only way to confirm a twin or multiple pregnancy is to see it by ultrasound. the only way you'll know for sure is to have an ultrasound.