Sex-selective abortion (also referred to as son preference or female deselection) are methods of sex-selection which are practiced in areas where male children are valued over female children. Sex-selective abortion refers to the targeted abortion of female fetuses; the fetus' sex may be identified by ultrasound but also rarely by amniocentesis or another procedure.
These practices arise in areas where cultural norms value male children over female children. Societies that practice sex selection in favor of males are quite common, especially in countries like the People's Republic of China, Korea, Taiwan, and India.
In 2005, 90 million women were estimated to be "missing" in Afghanistan, Bangladesh, China, India, Pakistan, South Korea and Taiwan alone, apparently due to sex-selective abortion. The existence of the practice appears to be determined by culture, rather than by economic conditions, because such deviations in sex ratios do not exist in sub-Saharan Africa, Latin America, and the Caribbean.
Sex-selective abortion was rare before the late 20th century, because of the difficulty of determining the sex of the fetus before birth, but ultrasound has made such selection easier. However, prior to this, parents would alter family sex compositions through infanticide. It is believed to be responsible for at least part of the skewed birth statistics in favor of males in mainland China, India, Taiwan, and South Korea. Even today, there are no scientifically proven and commercialized practices that allow gender detection during the first trimester, and ultrasound is fairly unreliable till approximately the 20th week of pregnancy. Consequently, sex selection often requires late term abortion of a fetus close to the limit of viability, making the practice frowned-upon even within the pro-choice community.
Somewhat controversially, the same sex-selection practices are also believed to occur among South Asian immigrants in the United States. A study of the 2000 United States Census observed definite male bias in families of Chinese, Korean and Indian immigrants, which was getting increasingly stronger in families where first one or two children were female. In those families where first two children were girls, the sex ratio of the third child was observed to be 1.51:1 in favor of boys. (To put the number in perspective, the 1.51:1 ratio could have been achieved if approximately 20% of all such families engaged in sex-selective abortion until they were able to conceive a boy.)
Sex-selective abortion, infanticide, and abandonment may not be the only causes of sex ratio imbalances in the countries mentioned above. Research indicates that women infected with the hepatitis B virus are 1.5 times more likely to give birth to a male. The researcher, Emily Oster, says that the higher rates of hepatitis B in China could account for 75% of the "missing girls." However, new demographic research casts doubt on the hepatitis B theory. Das Gupta found that data from a huge sample of births in China show that the only women with elevated probabilities of bearing a son are those who have already borne daughters.
In 2008, a new study by Emily Oster and Gang Chen showed her earlier theory was incorrect. "This ﬁnding leads me to conclude that hepatitis B cannot explain skewed sex ratios in China, and the conclusions about this in Oster (2005) were incorrect." 
Sex-selective abortion has become an issue in Southern and Eastern Asian countries, where sex-selective abortions have caused an increase in the imbalances between sex ratios of various Asian countries. Studies have estimated that sex-selective abortions have increased the ratio of males to females from the natural average of 105-106 males per 100 females to 113 males per 100 females in both South Korea and China, 110 males per 100 females in Taiwan and 107 males per 100 females among Chinese populations living in Singapore and parts of Malaysia. However, a similar trend does not exist in North Korea, possibly due to limited access to prenatal sex-testing technologies.
During the 1994 United Nations International Conference on Population and Development in Cairo, Egypt, policy objectives intended to eliminate sex-selective abortion and infanticide, along with discrimination against female children, were stated in Article 4.15 of the Programme of Action: "...to eliminate all forms of discrimination against the girl child and the root causes of son preference, which results in harmful and unethical practices regarding female infanticide and prenatal sex selection".
Sex-selective abortion has been seen as worsening the sex ratio in India, and thus affecting gender issues related to sex compositions of Indian households. According to the 2001 census, the sex-ratio in India is 107.8 males per 100 females, up from 105.8 males per 100 females in 1991. The ratio is significantly higher in certain states such as Punjab (126.1) and Haryana (122.0).
It has been argued that by having a one-child policy, China has increased the rate of abortion of female fetuses, thereby accelerating a demographic decline. As most Chinese families are allowed (that is, given extreme incentives to have) only one child, and would often prefer at least one son, there are fewer daughters, thus preventing the formation of a greater number of families in the next generation.
Since 2005, test kits such as the Baby Gender Mentor have become available over the internet. These tests have been criticized for making it easier to perform a sex-selective abortion earlier in a pregnancy. Concerns have also been raised about their accuracy.
While sex-selective abortion is controversial, even within the pro-choice community, some commentators have championed it as a means to empower women and increase familial happiness. For example, bioethicist Jacob M. Appel has written, "Mothers who want boys should have boys and mothers who want girls should have girls. Pre-implanting diagnosis offers the promising of increasing the number of children who are loved and wanted. I look forward to the day when every son knows that his parents wanted a son and every daughter knows that her parents wanted a daughter."