Here is one more reason for mothers to get back in the sunlight: the potential for low birth weight in their babies.
Low birth weight is associated with poor mood, anxiety, depression, high blood pressure and other problems during childhood and afterward. Recent research shows that low birth weight is related to exposure by pregnant women to winter temperatures during a critical developmental time for the fetus.  This could indicate vitamin D deficiency of the pregnant mother during “vitamin D winter,” the time of year in northern latitudes when the sun is too low in the sky to produce vitamin D. The answer, of course, is to use a tanning bed or take vitamin D3 supplements (3,000-5,000 IU) during the winter. Remember never to burn!
The child needs every possible advantage prior to birth, and one of the advantages is a mom with high vitamin D levels. The only source of vitamin D for the fetus is the mother’s body.
 Elter K, et al. Exposure to low outdoor temperature in the midtrimester is associated with low birth weight. Aust N Z J Obstet Gynecol 2004;44:553-7
 Murray, L. et al. Links of Season and outdoor ambient temperature: effects on birth weight. Obstet Gynecol. 2000 Nov;96(5 Pt 1):689-95