When your pregnant how can you tell if your too small?

what do you mean to small. do you mean to have the baby or not big enough weight wise for a healthy pregnancy? because i am 4''11 and 92 pounds and i pushed out an 8 pound baby.
If you're talking about size of the pelvis, then only a doctor or midwife can tell either by an internal examination, or ultrasound measurements. External body size is not necessarily an indication.

If it's baby's size you are referring to then that is difficult, with ultrasound being the best indicator. Externally feeling the baby can produce wildly varying judgments that often differ markedly once baby actually ends up on the scales! Just visually looking at your tummy is the worst indicator of all - so comments comparing women's 'baby bumps' are not at all helpful, as many factors affect this, including muscle tone, amount of fluid, and the position of the baby.