Since 1960 South Korea has experienced a dramatic decline in fertility resulting from rapid economic development and an efficient national family planning programs. The period total fertility rate (TFR) declined from six children per woman in 1960 to 1.7 in 1985, and has been below 1.3 since 2001. But fertility preference measured by mean ideal number of children declined modestly from five in 1960 to two in 1985 and has been slightly over two children since then. The combination of traditional patriarchal family system and rapidly declining fertility resulted in abnormally high sex ratio at birth for about 20 years since the mid-1980s, peaking at 117 in 1990. South Korean women report combining the traditional mother role and modern worker role to be very difficult, resulting in their stopping childbearing before achieving their preference. Since 2000, the proportion of women not marrying has increased substantially, but, once married, most women become mothers and stop childbearing after one or two children.