Researchers found that second children were less likely to be girls if the firstborn was a girl, according to the study published Monday in the Lancet, Britain's leading medical journal.
It also said the deficit in the number of girls born as a second child was more than twice as great among educated mothers than among illiterate ones.
Daughters traditionally belong to future husbands' families in India, which maintains the custom of dowry, and therefore are considered by many as a liability.
Dipankar Gupta, a sociologist, blamed the failure on the government's inability to implement laws against fetal sex determination and medical termination of pregnancy on the basis of gender.
"Everybody knows there are clinics where these tests are carried out. It's tantamount to murder. The guilty should be tried for that. The government has to be proactive to change people's attitude," he said.
Zoya Hasan, a professor of political science at Jawaharlal Nehru University in New Delhi, said the matter couldn't be dealt by the government alone.
"Civil society and various organizations have to intervene. However, the government has to ensure that tests for determining the sex of the child are now not allowed," she said. "Ultimately, it boils down to building public opinion and social consciousness that there is no difference between a man and a woman and protecting women's rights."
According to the report, the researchers studied data on female fertility from a continuing Indian national survey, analyzing information on 133,738 births.
Based on the natural gender ratio from other countries, they estimated that 13.6 million to 13.8 million girls should have been born in 1997 in India. However, 13.1 million were reported, the study said.
"We conservatively estimate that prenatal sex determination and selective abortion accounts for 0.5 million missing girls yearly," the study said.
"If this practice has been common for most of the past two decades since access to ultrasound became widespread, then a figure of 10 million missing female births would not be unreasonable," it said.
Ultrasound, used to check a fetus' health, can also find out its gender.
In India, fetal sex determination and medical termination of pregnancy on the basis of a fetus' gender have been illegal since 1994.
"However, there was ample published evidence of rampant sex determination and female feticide," it said.
The preference for boys has skewed the gender ratio in India, a nation of more than 1 billion people. The number of girls per 1,000 boys declined in the country from 945 in 1991 to 927 in 2001, according to government census-takers.