Artificial sweeteners

When used in moderation, artificial sweeteners are not harmful during pregnancy and while breastfeeding. 
Foods containing aspartame must be labelled with a warning "Contains a source of phenylalanine" (in Finnish: "Sisältää fenyylialaniinin lähteen") for people suffering from phenylketonuria (PKU). If your baby has been diagnosed with PKU, do not use aspartame while breastfeeding.