Worldwide rates of prematurity are more difficult to get. In developing countries, there is often no professional medical care for these babies. This makes it difficult to tell how far along the pregnancy really was. For this reason, the World Health Organization tracks rates of low birth weight instead. In 2000, 16.5 percent of babies born in developing countries were of low birth weight. It is estimated that one-third of these low birth weight deliveries are due to premature delivery.