Yes. Vitamin A is a nutrient that is essential for growth and development, so vitamin A supplements in moderate doses are safe for pregnant women.  Because beef liver is the most nutritious food out there, with over 25 vitamins and minerals in it, you can safely use freeze-dried liver supplements when you're pregnant. Humans have eaten liver as part of ancestral diets forever.  Just make sure to stick to a 1 to 2 ounce serving of liver per day, or 3 to 6 grams of a freeze-dried liver supplement if you’re pregnant to avoid getting too much vitamin A. And make sure you're getting enough vitamin D as well.   You should also make sure you check with your healthcare provider before adding any supplements beyond your prenatal vitamin when you're pregnant.