How do you know you are having twins
With the advance in technology and health system, it is very rare these days to have a surprise twin pregnancy.
Most people will know they are having twins from the beginning or at least form week 16 when a routine ultrasound is scheduled in most parts of the western world.
You may end up having an ultrasound test earlier if your doctor suspects twins, as it was in my case. I believe when you do the blood test to confirm your pregnancy and the HCG levels (pregnancy hormones) are too high, it can either indicate a twin pregnancy, or you have been pregnant longer than you thought.
Even if you do not have any ultrasound test, at some point with regular check ups your doctor will hear two very distinct heart beats.
Also your tummy size is a good indicator of what you are carrying in there ladies!
Another possible indication of twin pregnancy is that your morning sickness and other early pregnancy symptoms may be exaggerated like severe nausea and vomiting. If you suspect a multiple pregnancy just ask your doctor to confirm your suspicious.