What will happen if i don't gain enough weight in pregnancy?

Baby may suffer: Recommended wt gain depends on base weight before preg. Too little gain may effect babies growth and nutrition. If your nutrition is compromised resulting in too little gain, you may suffer in child birth. Excess tearing or lacerations have been noted with poor nutrition esp. Low protein intake.

Usually nothing: Usually you'll be ok, but check w/your OB if you're concerned. The "best" pregnancy is usually a slow sustained weight gain.