Practically every expecting woman is recommended a daily prenatal vitamin. Doctors know that it's possible for a woman to cover all of her nutritional needs with a well balanced diet but they also know that no woman possesses the perfect diet.
Maybe the diet plan of yours would be enough in case you don't ate on the run, never felt overly sick to eat, you knew you had been merely pregnant with only one child, or perhaps when you were living in lab where all the food of yours was particular caloric needs were estimated along with your food was weighed and measured on the actual amount.