The baby's lungs are not fully developed. While in the womb the fetus is supplied with oxygen and nutrients through the umbilical cord. Starting in the third trimester, the fetus does make the motions of breathing, and in this way moves amniotic fluid in and out of her lungs. This activity can sometimes be seen on ultrasound examination. The flow of amniotic fluid into the lungs is believed to be important in fetal lung development. Before birth, these breathing movements have nothing to do with getting oxygen. The fetus gets her oxygen from her mother, through the placenta and umbilical cord. True breathing begins just after birth, as the fetus turns into a baby and takes her first breath of air. The baby can not make the sounds of crying while still in the womb, but studies have shown that "crying behavior" can happen while inside the womb. With the help of video-recorded ultrasound images, the investigators found that a group of third-trimester fetuses showed evidence of "crying behavior" in response to a low-decibel noise played on the mother's abdomen. Fetuses showed a "startle" response to the noise, along with deep inhalations and exhalations, an open mouth and a "quivering" chin --- all signs of crying.