Doctors have also vastly improved their technologies for keeping preemies alive. In the 1970's, fewer than 20 percent of newborns weighing less than 2.2 pounds -- approximately three months premature -- survived. In the three decades since then, improvements in the technology have boosted the survival rate to 70 percent, and it is even higher for babies born closer to term. (For unknown reasons, girls do a little better than boys.) In rare cases, doctors are saving even smaller babies, who would have had no chance only a few years ago. In September 2004, for example, a Chicago woman gave birth to a baby girl weighing only 8.6 ounces: she was small enough to curl up inside a toddler's slipper. Dr. Jonathan Muraskas, a neonatal specialist at Loyola University Medical Center near Chicago, was convinced that he could save the girl. She was discharged on Feb. 8, weighing 5 pounds 8 ounces -- more than 10 times what she weighed when she was born five months earlier.