The temperature inside the uterus is between a third and half a degree higher than yours. Because your body temperature is so closely controlled, your baby never becomes cold so never needs to shiver. He has started to lay down a special form of brown fat, particularly around the neck, chest, and back. After birth, metabolism of this fat produces both energy and heat. In the uterus, however, the baby cannot use this fat to raise his temperature. Some temperature control occurs as heat is lost from the baby's skin into the amniotic fluid through the uterine wall and then into your body tissues. However, the regulation of temperature is predominantly achieved by means of the blood flow to the placenta. The large surface area of the placenta allows it to act as a heat exchange, keeping the temperature of the blood leaving the baby in the umbilical arteries constant with that of the oxygenated blood returning to the baby through the umbilical vein.
After birth, babies lose heat quickly. They are still unable to shiver and cannot maintain their temperature, cooling rapidly if they're not wrapped up warmly or held skin-to-skin shortly after the birth.