Sex selection can take place before a pregnancy is established, during pregnancy through prenatal sex detection and selective abortion, or following birth through infanticide or child neglect. Sex selection is sometimes used for family balancing purposes but far more typically occurs because of a systematic preference for boys. The biologically normal sex ratio at birth ranges from 102 to 106 males per 100 females. However, ratios higher than normal –sometimes as high as 130 –have been observed. This is now causing increasing concern in some South Asian, East Asian and Central Asian countries.