It is advised to not feed children foods with aspartame because of their high caloric needs. During pregnancy, you also have high caloric needs. Hearing that you eat a low calorie yogurt worries me that you may be watching your caloric intake a little too closely. I just want to advise you to make sure you are getting enough calories, and that about 30 percent of them come from fat. At your stage in pregnancy, you should probably be gaining about one pound per week if you were at a good weight for your height before pregnancy.
Amino acids make up proteins.
The chemical configuration of aspartame is different from that of a protein. For example, the same substances can be found in milk, fruits, and vegetables. Some of the breakdown products may cross the placenta, but studies show that the amount is insignificant, and therefore, determined to be safe. Eating foods with aspartame is a personal choice. Some people feel it is safe because the results of studies show that to be the case.