It is best to speak with your doctor before taking dandelion during pregnancy. No formal safety studies around this have been performed with women who are pregnant and it is, therefore, advised to stay away from dandelion greens during pregnancy.
Taking common medicines during pregnancy, a summary of NHS UK guidelines
You should definitely check with your doctor before taking any medication during pregnancy. Even for medication you were already on at the time of getting pregnant, now needs to be approved by your doctors as