Survivors of immaturity of outstanding intelligence include Fortunio Licetus, born in 1577, and Isaac Newton, born in 1643. Reliable descriptions began appearing around 1820, and over a dozen infants were born weighing under 1000 g and before World War II, who developed normally. From 1876 to 2006, the birth weight at which half of the infants survived dropped from 2200 to 600 g. Statistics depended on how abortion, stillbirth and live birth were defined, which differed greatly from country to country. WHO definitions in 1993 required the registration of all infants weighing 500 g (22 complete weeks) or above. This definition was not universally adopted, resulting in considerable underreporting. Many medical societies issued ethical recommendations concerning the obligatory or optional treatment of immature infants. The “window”, at which treatment is optional has been set at 22–23 weeks (Japan, Germany), 23–24 weeks (UK, USA, Canada), or 24–26 weeks (France, Netherlands, Switzerland). Instead of assessing an infant's individual prognosis, and ignoring its gender, co-morbidities, and particular cause of premature delivery, these rules frequently relied on gestational age alone to initiate or withhold life support.