Vitamin D is necessary for maintaining strong muscles, bones and teeth. It also helps your body to absorb calcium. Vitamin D is contained in some foods, namely sardines, mackerel, eggs, margarine and milk. Many pregnant women are deficient in Vitamin D due to the expanded plasma volume of pregnancy and our limited sun exposure as we work indoors.
Most of our Vitamin D comes from the sun and it is recommended to have a few minutes exposure every day. A simple blood test can determine if you are deficient in Vitamin D and a Vitamin D supplement will be recommended if you are.
http://www.healthdirect.gov.au/vitamin-d-deficiency