Yes the doctor can assess the growth of the baby with external examination. Loosing weight means ensuring that you eat right and exercise so that your fats get converted to pregnancy requirements. You may not loose on the scale but if you do not gain weight then it translates to the weight being contributed towards pregnancy. You can also focus on high protein foods to help the baby gain weight.

I advised to u,u can do the exercise prescribed by the doctor it will gives u a easy and pleasant delivery to uu

sorry I may not have an exact answer to ur query but I am in an opp situation.. my baby is measuring two weeks ahead n doc said the more I eat the more the baby will gain so i m required to not gain too much. so I M not sure how exactly will your baby put on if ur not eating.