Herring is an important source of vitamin D. Having herring during pregnancy prevents vitamin D deficiency and helps improve your immunity. Herring is also rich in iron and vitamin B-12 that keep your red blood cells healthy. It also contains calcium, magnesium and phosphorus which are important for your baby’s skeletal growth. Its potassium content also helps your nerve cells in transmitting electrical signals. Hence, pregnant women can certainly have 8-12 ounces of thoroughly cooked herring during the 9 months.