Reproductive technology that allows parents to know the gender of their fetus has led to a shortage of 117 million women in Asia, particularly in China and India, the Agence France-Presse reported Thursday.

The trend is expected to have lasting impact on these countries for at least the next 50 years, according to experts at a UN and Vietnam conference in Hanoi.

"This skewed population sex ratio reflects a preference for sons, in combination with increasing access to new sex-selection technology,” the UN Population Fund wrote in a conference paper.

Increasing access to ultrasounds and other reproductive technology has contributed to the rise of “selective abortions,” said French demographer Christophe Guilmoto, in which parents abort fetuses based on their sex.

In Asian countries such as China, where boys are favored and couples are only allowed to have one child, this means that parents typically choose to abort girls in order to give birth to boys.

In most countries, the sex ratio at birth ranges from 104 to 106 male births for every 100 females, but over the past 25 years, the imbalance has gradually increased, the UN said.

UN data from the past few years show that China now has 118.1 male babies for 100 females, India 110.6, Azerbaijan 117.6 and Vietnam 111.2.

In addition, female infants in these countries tend to have a much higher death rate than their male counterparts.

"Postnatal discrimination - expressed through excess deaths among female infants and young girls - has not entirely disappeared from several countries and reflects the relative neglect of female children," Guilmoto said.

According to the UN, the preference for sons in Asian countries reflect socio-economic influences and antiquated traditions in which sons alone inherit property, care for aging parents and so forth, while daughters require dowries and leave their families once married.

Even if the sex ratio at birth returned to normal within the next decade, Chinese and Indian men would still face a “marriage squeeze” for several decades afterward, the researchers said.

"Not only would these men have to marry significantly older, but this growing marriage imbalance would also lead to a rapid rise in male bachelorhood. . . an important change in countries where almost everyone used to get married," Guilmoto said.

Though some countries, such as Vietnam, prohibit fetal sex determination, these bans are often difficult to reinforce. Other Asian countries like Korea, which have returned to near-normal sex ratios are “unique,” the researchers said.

"Dealing with the future demographic consequences of past and present sex imbalances at birth and their societal impact may soon become the next challenge to respective governments," Guilmoto said.

Click here to read more from the AFP.